Prof. M. Padmanabhan currently serves as Professor in the Department of Chemistry, School of Arts and Science, Amritapuri Campus.

 

 

 

Position held / Experiences

  • Dean, Faculty of Sciences, Mahatma Gandhi University, Kottayam, Kerala
  • Professor and Director, School of Chemical Sciences, Mahatma Gandhi University (1996-2006)
  • Visiting Professor, Rutgers University, New Jersey, USA (2006-2009)
  • Visiting Professor, IISER, Trivandrum
  • Visiting Professor, IIST, ISRO, Trivandrum
  • Visiting Professor, M G University
  • Adjunct Faculty Professor, Amrita Vishwa Vidyapeetham
  • Visiting Professor, Amrita Vishwa Vidyapeetham
  • Chairman, Board of Studies, Chemistry (P G programs) M G University
  • Chairman, Board of Studies, Chemical Sciences (P G programs), M G University
  • Chief, University Employment and Guidance Bureau, M G University
  • Officer, CSIR Scientists’ Pool, Indian Institute of Science, Bangalore
  • Post-doctoral research: University of Erlangen, Nurnberg, Germany
  • Officer, CSIR Scientists’ Pool, NIIST (erstwhile RRL), CSIR, Trivandrum
  • Ph D Research (IIT Madras) (1972 - 1977)
     

Teaching Areas

  • Inorganic Chemistry
  • Coordination Chemistry
  • Main Group Elements Chemistry
  • Organometallics
  • Bio-inorganic Chemistry
  • Spectroscopy
     

Awards/Honors/Achievements

  • University First Rank for M Sc
  • National and State Merit Scholarships
  • CSIR JRF, SRF and Post-doctoral Fellowships
  • German Research Council Research Associateship
  • Nature Publishing Group Award (2006 Inorganic Chemistry Gordon Research Conference, Newport, USA)

 

Publications

Publication Type: Journal Article
Year of Publication Publication Type Title
2016 Journal Article S. Sankar, Nair, B. N., Suzuki, T., Anilkumar, G. M., M. Padmanabhan, Harish, S., and Warrier, K. Ga, “Hydrophobic and metallophobic surfaces: Highly stable non-wetting inorganic surfaces based on lanthanum phosphate nanorods”, Scientific Reports, vol. 6, 2016.[Abstract]

Metal oxides, in general, are known to exhibit significant wettability towards water molecules because of the high feasibility of synergetic hydrogen-bonding interactions possible at the solid-water interface. Here we show that the nano sized phosphates of rare earth materials (Rare Earth Phosphates, REPs), LaPO 4 in particular, exhibit without any chemical modification, unique combination of intrinsic properties including remarkable hydrophobicity that could be retained even after exposure to extreme temperatures and harsh hydrothermal conditions. Transparent nanocoatings of LaPO 4 as well as mixture of other REPs on glass surfaces are shown to display notable hydrophobicity with water contact angle (WCA) value of 120° while sintered and polished monoliths manifested WCA greater than 105°. Significantly, these materials in the form of coatings and monoliths also exhibit complete non-wettability and inertness towards molten metals like Ag, Zn, and Al well above their melting points. These properties, coupled with their excellent chemical and thermal stability, ease of processing, machinability and their versatile photo-physical and emission properties, render LaPO 4 and other REP ceramics utility in diverse applications.

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2016 Journal Article U. Arjun, Brinda, K., M. Padmanabhan, and Nath, R., “Magnetic properties of layered rare-earth oxy-carbonates Ln2O2CO3 (Ln=Nd, Sm, and Dy)”, Solid State Communications, p. -, 2016.[Abstract]

Abstract Polycrystalline samples of rare-earth oxy-carbonates Ln2O2CO3 (Ln=Nd, Sm, and Dy) are synthesized and their structural and magnetic properties are investigated. All of them crystallize in a hexagonal structure with space group P 6 3 / mmc . They form a double layered structure with frustrated triangular arrangement of rare-earth magnetic ions. An antiferromagnetic transition is observed at T N   1.25 K , 0.61 K , and 1.21 K for Nd2O2CO3, Sm2O2CO3, and Dy2O2CO3, respectively. From the analysis of magnetic susceptibility, the value of the Curie–Weiss temperature θ \{CW\} is obtained to be  21.7 K, 18 K, and 10.6 K for Nd2O2CO3, Sm2O2CO3, and Dy2O2CO3, respectively. The magnetic frustration parameter f ( = | θ \{CW\} | / T N ) is calculated to be  17.4, 31, and 8.8 for Nd2O2CO3, Sm2O2CO3, and Dy2O2CO3, respectively, which indicates that Sm2O2CO3 is strongly frustrated compared to its Nd and Dy analogues. More »»
2015 Journal Article R. Nath, M. Padmanabhan, Baby, S., Thirumurugan, A., Ehlers, D., Hemmida, M., Von Nidda, K., .-A., H., ,, and .A., A., “Quasi-two-dimensional S = 1/2 magnetism of Cu[C6H2(COO)4][C2H5 NH3]2”, Physical Review B - Condensed Matter and Materials Physics, vol. 91, 2015.[Abstract]

We report structural and magnetic properties of the spin-1/2 quantum antiferromagnet Cu[C6H2(COO)4][C2H5NH3]2 by means of single-crystal x-ray diffraction, magnetization, heat capacity, and electron-spin-resonance (ESR) measurements on polycrystalline samples, as well as band-structure calculations. The triclinic crystal structure of this compound features CuO4 plaquette units connected into a two-dimensional framework through anions of the pyromellitic acid [C6H2(COO)4]4-. The ethylamine cations [C2H5 NH3]+ are located between the layers and act as spacers. Magnetic susceptibility and heat capacity measurements establish a quasi-two-dimensional, weakly anisotropic, and nonfrustrated spin-1/2 square lattice with the ratio of the couplings Ja/Jc ≃ 0.7 along the a and c directions, respectively. No clear signatures of the long-range magnetic order are seen in thermodynamic measurements down to 1.8 K. However, the gradual broadening of the ESR line suggests that magnetic ordering occurs at lower temperatures. Leading magnetic couplings are mediated by the organic anion of the pyromellitic acid and exhibit a nontrivial dependence on the Cu-Cu distance, with the stronger coupling between those Cu atoms that are farther apart. © 2015 American Physical Society.

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2015 Journal Article M. O. Ajeesh, Yogi, A., M. Padmanabhan, and Nath, R., “Tuning of magnetic frustration in S = 1 / 2 Kagomé lattices {[Cu3(CO3)2(bpe)3](CLO4)2}n and {[Cu3(CO3)2(bpy)3](CLO4)2}n through rigid and flexible ligands”, Solid State Communications, vol. 207, pp. 16-20, 2015.[Abstract]

Single crystalline and polycrystalline samples of S=1/2 Kagomé lattices {[Cu3(CO3)2(bpe)3](CLO4)2}n and {[Cu3(CO3)2(bpy)3](CLO4)2}n, respectively were synthesized. Their structural and magnetic properties were characterized by means of x-ray diffraction and magnetization measurements. Both compounds crystalize in a hexagonal structure (space group P-6) consisting of CuO4 Kagomé layers in the ab-plane but linked along c direction through either rigid bpy or flexible bpe ligands to form 3D frame works. Magnetic measurements reveal that both the compounds undergo ferromagnetic ordering (TC) at low temperatures and the TC and the extent of frustration could be tuned by changing the nature of the pillar ligands. {[Cu3(CO3)2(bpe)3](CLO4)2}n which is made up of flexible bpe ligands has a TC of 5.7 K and a Curie-Weiss temperature (θCW) of -39.7 K giving rise to a frustration parameter of |θCW|/TC≈6.96. But the replacement of bpe by a more rigid and electronically delocalized bpy ligand leads to an enhanced TC≈9.3K and a reduced frustration parameter of |θCW|/TC≈3.54. © 2015 Published by Elsevier Ltd.

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2013 Journal Article R. Nath, Tsirlin, A. A., Khuntia, P., Janson, O., Forster, T., M. Padmanabhan, Li, J., Skourski, Y., Baenitz, M., Rosner, H., and Rousochatzakis, I., “Magnetization and spin dynamics of the spin S=1/2 hourglass nanomagnet Cu 5 (OH) 2 (NIPA) 4 10H 2 O”, Physical Review B, vol. 87, p. 214417/115, 2013.[Abstract]

We report a combined experimental and theoretical study of the spin S=12 nano magnet Cu5(OH)2(NIPA)4⋅10H2O (Cu5-NIPA). Using thermodynamic, electron spin resonance, and 1H nuclear magnetic resonance measurements on one hand, and ab initio density-functional band-structure calculations, exact diagonalizations, and a strong-coupling theory on the other, we derive a microscopic magnetic model of Cu5-NIPA and characterize the spin dynamics of this system. The elementary fivefold Cu2+ unit features an hourglass structure of two corner-sharing scalene triangles related by inversion symmetry. Our microscopic Heisenberg model comprises one ferromagnetic and two antiferromagnetic exchange couplings in each triangle, stabilizing a single spin S=12 doublet ground state (GS), with an exactly vanishing zero-field splitting (by Kramers' theorem), and a very large excitation gap of Δ≃68 K. Thus, Cu5-NIPA is a good candidate for achieving long electronic spin relaxation (T1) and coherence (T2) times at low temperatures, in analogy to other nanomagnets with low-spin GS's. Of particular interest is the strongly inhomogeneous distribution of the GS magnetic moment over the five Cu2+ spins. This is a purely quantum-mechanical effect since, despite the non frustrated nature of the magnetic couplings, the GS is far from the classical collinear ferrimagnetic configuration. Finally, Cu5-NIPA is a rare example of a S=12 nano magnet showing an enhancement in the nuclear spin-lattice relaxation rate 1/T1 at intermediate temperatures.

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2013 Journal Article M. S. Suresh and M. Padmanabhan, “Synthesis and characterization of axially linked heteroleptic polymeric and monomeric lewis base adducts of BIS-(2-mercaptobenzothiazolato) Nickel(II) and its extraordinary thermal decomposition”, Asian Journal of Chemistry, vol. 25, pp. 7669-7674, 2013.[Abstract]

{Six coordinated axially bridged heteroleptic polymeric and monomeric Lewis base adducts from coordinatively unsaturated bis-(2-mercaptobenzothiazolato) nickel(II) {Ni(mbt)2, [NiC14H8N 2S4]} have been synthesized and charecterized by elemental analysis, spectral techniques, magnetic susceptibility measurements and thermal analysis using coordination sphere expansion method. These adducts have general molecular formula [Ni(mbt)2L]n for polymeric adducts and [Ni(mbt)2L2] for monomeric adducts, where L = pyrazine, 4,4′-bipyridine and 4,4′-azopyridine

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2013 Journal Article S. L. Linguito, Zhang, X., M. Padmanabhan, Biradar, A. V., Li, J., Xu, T., Emge, T. J., and Asefa, T., “New polyoxomolybdate compounds synthesized in situ using ionic liquid 1-butyl-3-methyl-imidazolium tetrafluoroborate as green solvent”, New Journal of Chemistry, vol. 37, pp. 2894-2901, 2013.[Abstract]

Herein we report the facile, green syntheses of three new polyoxomolybdate-based inorganic-organic hybrid materials using room temperature ionic liquid (RTIL), 1-butyl-3-methyl-imidazolium tetrafluoroborate (bmim)[BF4], as a green and reactive solvent. The organic imidazolium component of the RTIL was incorporated into all three structures, the μ5-oxo octamolybdate cluster compound (bmim)3NH 4[Mo8O26] (1) and two Keggin-type cluster compounds, one being a charge transfer salt (bmim)4[PMo VMo11O40] (2) and the other having the unreduced anion (bmim)3[PMo12O40] (3). Phase pure and highly crystalline samples were obtained. In 1 the Mo8O 26 moiety is a tetranionic cluster in its β phase. Compound 1 contains three bmim cations and an NH4 + molecule to complement the -4 charge on the octamolybdate anion. The α-phase Keggin-type anion in 2, [PMoVMo11O40] 4-, contains one Mo atom in the +5 oxidation state, indicating that 2 is a charge transfer complex. The α-phase Keggin-type anion in 3, [PMo12O40]3-, has 12 fully-oxidized Mo atoms. Compound 3 has a band gap ∼3.5 eV. The catalytic nature of compound 3 in the oxidation of styrene to benzaldehyde was investigated. The maximum styrene conversion was 83%, while the maximum selectivity to benzaldehyde was 96.5%. The catalyst was successfully used for five cycles without significant loss in activity or selectivity. The structure of the catalyst remains unchanged after repeated use. Our work points to the feasibility of generating a wide variety of new and useful POM-based compounds through a 'green' synthesis route. © 2013 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

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2013 Journal Article R. Nath, Tsirlin, A. A., Khuntia, P., Janson, O., Förster, T., M. Padmanabhan, Li, J., Skourski, Y., Baenitz, M., Rosner, H., and Rousochatzakis, I., “Magnetization and spin dynamics of the spin S=12 hourglass nanomagnet Cu5(OH)2(NIPA)4·10H2O”, Physical Review B - Condensed Matter and Materials Physics, vol. 87, 2013.[Abstract]

We report a combined experimental and theoretical study of the spin S=12 nanomagnet Cu5(OH)2(NIPA)4·10H 2O (Cu5-NIPA). Using thermodynamic, electron spin resonance, and 1H nuclear magnetic resonance measurements on one hand, and ab initio density-functional band-structure calculations, exact diagonalizations, and a strong-coupling theory on the other, we derive a microscopic magnetic model of Cu5-NIPA and characterize the spin dynamics of this system. The elementary fivefold Cu2+ unit features an hourglass structure of two corner-sharing scalene triangles related by inversion symmetry. Our microscopic Heisenberg model comprises one ferromagnetic and two antiferromagnetic exchange couplings in each triangle, stabilizing a single spin S=12 doublet ground state (GS), with an exactly vanishing zero-field splitting (by Kramers' theorem), and a very large excitation gap of Δ≠68 K. Thus, Cu5-NIPA is a good candidate for achieving long electronic spin relaxation (T1) and coherence (T2) times at low temperatures, in analogy to other nanomagnets with low-spin GS's. Of particular interest is the strongly inhomogeneous distribution of the GS magnetic moment over the five Cu2+ spins. This is a purely quantum-mechanical effect since, despite the nonfrustrated nature of the magnetic couplings, the GS is far from the classical collinear ferrimagnetic configuration. Finally, Cu5-NIPA is a rare example of a S=12 nanomagnet showing an enhancement in the nuclear spin-lattice relaxation rate 1/T1 at intermediate temperatures. © 2013 American Physical Society.

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2012 Journal Article M. S. Suresh and M. Padmanabhan, “Synthesis, thermal and spectral characterization of axially bridged polymeric and monomeric Lewis base adducts of bis (2-mercaptobenzothiazolato) cobalt (II)”, Rasayan Journal of Chemistry, vol. 5, pp. 311-320, 2012.[Abstract]

Octahedrally coordinated monomeric and axially bridged polymeric compounds from four coordinated cobalt(H) species have been synthesized and characterized by elemental analysis, infra red and electronic spectroscopy, magnetic susceptibility measurements and thermal analysis. The four coordinated system used was tetrahedral bis(2-mercaptobenzothiazolatocobalt(II), Co(mbt) 2 and ligands used were bidentate opposite end donors such as 4-aminopyridine, 4,4'-bipyridine and pyrazine. For comparison a monodentate ligand pyridine was also used. The complexes synthesized have the molecular formula [CoCmbt) 2L2] where L= pyridine and 4-aminopyridine and [Co(mbt)2L']n where L'= pyrazine and 4,4'-bipyridine. The infra red and thermal studies indicate that 4-aminopyridine is coordinated through its pyridyl nitrogen only, eventhough it is bidentate while others behave as bridging bidentate. These adducts have a trans octahedral structure which is preferable for extended linear framework, eventhough two isomeric forms are possible viz. cis and trans. The variation of magnetic moment on adduct formation was also carried out The thermal decomposition of Co(mbt)2 is seen taking place in two stages, in nitrogen atmosphere, with CoS, a stable residue. In the case of adducts an additional step was observed due to the loss Lewis bases used. The kinetic and mechanistic parameters were also evaluated from different decomposition stages. In most of the cases it follows Random nucleation, one nucleus on each particle obeying Mampel equation. © 2012 RASÄYAN. All rights reserved.

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2011 Journal Article Y. Zhao, M. Padmanabhan, Gong, Q., Tsumori, N., Xu, Q., and Li, J., “CO catalytic oxidation by a metal organic framework containing high density of reactive copper sites”, Chemical Communications, vol. 47, pp. 6377-6379, 2011.[Abstract]

A new metal organic framework containing high density of active Cu sites demonstrates 100% oxidative conversion of CO to CO2. © 2011 The Royal Society of Chemistry. More »»
2011 Journal Article A. Lan, M. Padmanabhan, Li, K., Wu, H., Emge, T. J., Hong, M., and Li, J., “Two-dimensional coordination polymers of Zn(II) and Cd(II) derived from 3,3′,5,5′-azobenzenetetracarboxylic acid exhibiting solvent facilitated structure reversibility”, Inorganica Chimica Acta, vol. 366, pp. 68-75, 2011.[Abstract]

Two Cd(II) and Zn(II) coordination polymers based on 3,3′,5,5′- azobenzenetetracarboxylic acid (H4abtc): [Cd2(abtc)(H 2O)6]·DMF·0.5H2O (1) and [Zn 2(abtc)(bpy)(H2O)2]·DMF·H 2O (2) are synthesized and structurally characterized. Both 1 and 2 are 2D polymers but interconnected by solvent molecules to generate 3D suprastructures. Solvent expulsion leads to rupture of both structures, but upon re-exposure to the solvent mixture they exhibit remarkable ability to regain the original structure reversibly from the almost amorphous solvent-expelled form. Compounds with such structural flexibility and reversibility are expected to have some useful functionality. © 2010 Elsevier B.V. All rights reserved. More »»
2010 Journal Article P. Parameswar Nampi, M. Padmanabhan, Berry, F. John, Mortimer, M., and Warrier, K. Gopakumar, “Aluminosilicates with varying alumina-silica ratios: synthesis via a hybrid sol-gel route and structural characterisation”, Dalton Transactions, vol. 39, pp. 5101-5107, 2010.[Abstract]

Aluminosilicates with varying Al2O3:SiO2 molar ratios (3 : 1{,} 3 : 2{,} 3 : 3 and 3 : 4) have been synthesized using a hybrid sol-gel route using boehmite sol as the precursor for alumina and tetraethyl orthosilicate (TEOS) as the precursor for silica. The synthesis of boehmite sol from aluminium nitrate{,} and its use as the alumina precursor{,} is cost effective compared to alkoxide precursors. Structural aspects{,} including bonding and coordination{,} are studied in detail for samples calcined in the temperature range 400-1400 [degree]C using both NMR and FTIR spectroscopy: the results are correlated with phase formation data (spinel and high temperature phases) obtained from XRD and thermal analysis. FTIR results show a broadening of peaks at 800 [degree]C indicating a disordered distribution of octahedral sites caused by crosslinking between AlO6 octahedral and SiO4 tetrahedral units prior to the formation of mullite. 27Al MAS NMR spectra are consistent with a progressive decrease in the number of AlO6 polyhedra with increasing temperature corresponding to Al in these units being forced to adopt a tetrahedral coordination due to the increasing presence of similarly coordinated Si species. XRD results confirm the formation of pure mullite at 1250 [degree]C for a 3Al2O3:2SiO2 system. At 1400 [degree]C{,} phase pure mullite is observed for all compositions except 3Al2O3:SiO2 where [small alpha]-Al2O3 is the major phase with traces of mullite. The synthesis of aluminosilicates through a hybrid sol-gel route and the detailed insight into structural features gained from spectroscopic and diffraction techniques contributes further to the development of these materials in applications ranging from nanocatalysts to high-temperature ceramics. More »»
2009 Journal Article P. Padmaja, Warrier, K. G. K., M. Padmanabhan, and Wunderlich, W., “High surface area sol-gel alumina-titania nanocatalyst”, Journal of Sol-Gel Science and Technology, vol. 52, pp. 88-96, 2009.[Abstract]

Alumina-titania mixed oxide nanocatalysts with molar ratios = 1:0.5, 1:1, 1:2, 1:5 have been synthesized by adopting a hybrid sol-gel route using boehmite sol as the precursor for alumina and titanium isopropoxide as the precursor for titania. The thermal properties, XRD phase analysis, specific surface area, adsorption isotherms and pore size details along with temperature programmed desorption of ammonia are presented. A specific surface area as high as 291 m2/g is observed for 1:5 Al2O3/TiO2 composition calcined at 400 °C, but the same composition when calcined at 1,000 °C, resulted in a surface area of 4 m2/g, while 1:0.5 composition shows a specific surface area of 41 m2/g at 1,000 °C. Temperature programmed desorption (of ammonia) results show more acidic nature for the titania rich mixed oxide compositions. Transmission electron microscopy of low and high titania content samples calcined at 400 °C, shows homogeneous distribution of phases in the nano range. In the mixed oxide, the particle size ranges between 10-20 nm depending on titania content. The detailed porosity data analysis contributes very much in designing alumina-titania mixed oxide nanocatalysts. © 2009 Springer Science+Business Media, LLC. More »»
2008 Journal Article M. Padmanabhan, Joseph, J. C., Huang, X., and Li, J., “Diamine incorporated compounds derived from polymeric nickel(II) fumarates and oxalates: Crystal structure, spectral and thermal properties of [Ni(en)3](O2C{single bond}CH{double bond, long}CH{single bond}CO2)·3H2O and [Ni(en)3](O2C{single bond}CO2)”, Journal of Molecular Structure, vol. 885, pp. 36-44, 2008.[Abstract]

{Lewis-base mediated fragmentation of polymeric nickel(II) fumarate and oxalate are attempted using chelating σ-donor diamines like ethylenediamine (en) and 1,3-diaminopropane (dap) in various conditions which yielded [Ni(en)3](fum)·3H2O (1), [Ni(en)3](ox) (2), [Ni(dap)2(fum)] (3) and [Ni(dap)(ox)]·2H2O (4). While 1 and 2 are molecular products each containing octahedral [Ni(en)3]2+ moieties and the anionic dicarboxylate species, 3 and 4 are dap-incorporated polymeric products. The fumarate derivative 1 containing [Ni(en)3]2+ moieties crystallizes in the monoclinic space group C2/c with a = 17.899(4) Å More »»
2008 Journal Article M. Padmanabhan, Joseph, J. C., Thirumurugan, A., and Rao, C. N. R., “Maleate-fumarate conversion and other novel aspects of the reaction of a Co(ii) maleate with pyridine and bipyridine”, Dalton Transactions, pp. 2809-2811, 2008.[Abstract]

Reaction of a molecular Co(ii) maleate, [Co(Hmal)2(H 2O)4], with pyridine yields a Co(ii) fumarate, [Co(fum)(H2O)4], with a chain structure and a chiral pyridylsuccinic acid zwitter ion, -OOC-CH(N+C 5H5)-CH2-COOH, in almost quantitative yields, while the reaction of 4,4′-bipyridine (bipy) with the Co(ii) maleate, on the other hand, almost quantitatively generates a polylmeric Co(ii) maleate, [Co(mal)(bipy)]n•(n/2)H2O along with the adduct of fumaric acid with bipyridine. © The Royal Society of Chemistry. More »»
2008 Journal Article M. Padmanabhan, Joseph, J. C., Olsson, S., and Bakir, M., “Catena-Poly[[[aqua(propane-1,3-diamine-κ2 N,N′)copper(II)]-μ-fumarato-κ2 O:O′] monohydrate]”, Acta Crystallographica Section E: Structure Reports Online, vol. 64, pp. m303-m304, 2008.[Abstract]

The asymmetric unit of the title compound, {[Cu(C4H2O4)(C3H10N2)(H2O)] ·H2O} n , consists of two CuII atoms, half each of two propane-1,3-diamine ligands and two coordinated water mol-ecules, all lying on crystallographic mirror planes, also one fumarate dianion and one uncoordinated water mol-ecule in a general position. The Cu(C3H10N2)(H2O) units are linked via fumarate dianions into a zigzag chain running along the a axis. A longer Cu - O distance [2.873 (3) Å] is to a water mol-ecule bridging equivalent CuII atoms in adjacent chains, forming a three-dimensional framework. One of the CuII atoms is in a distorted square-pyramidal environment and the other is in a pseudo-octa-hedral geometry of the [5+1] type. O - H⋯O and N - H⋯O hydrogen bonds are observed in the crystal structure. More »»
2007 Journal Article M. Padmanabhan, Joseph, K. C., Puranik, V. G., Huang, X., and Li, J., “An unprecedented two-dimensional polymeric [Zn(OOC-C6H4-COO)2]n 2-[+H3N-(CH2)3-NH3 +]n system bearing one-dimensional chain of zinc(II) bis(phthalate) dianions held by propane-1,3-diammonium cations: Crystal structure, thermal and fluorescent properties”, Solid State Sciences, vol. 9, pp. 491-495, 2007.[Abstract]

A novel zinc(II) phthalate compound, [Zn{C6H4(COO)2}2]n 2-[NH3-(CH2)3-NH3]n 2+, 1 which contains four different phthalate moieties coordinated to the Zn(II) ion through one each of their carboxylate moieties in a η1-form and each phthalate moiety acting as a bridging unit with an overall tetrahedral geometry around the metal ion has been prepared and structurally characterized. The structure is unique in the sense that the dianionic moieties [Zn{C6H4(COO)2}2]2- form an infinite one-dimensional network composed of 14-membered cyclic units interconnected in a way that they are disposed alternatively in almost perpendicular planes. The dicationic [NH3-(CH2)3-NH3]2+ units are seen to hold these one-dimensional chains by strong coulombic and hydrogen bond interaction, resulting in an infinite two-dimensional layered structure of 1. The compound is thermally stable up to 250 °C. Above this temperature it loses one equivalent of phthalate moiety along with the diammonium unit to yield Zn(II) phthalate. The thermodynamic and kinetic parameters associated with this process could be evaluated using Coats-Redfern equation which shows the activation energy Ea for the process as 305.0 kJ mol-1, the frequency factor A as 1.49 × 1011 s-1 and the entropy change ΔS as -35.90 JK-1 mol-1. Fluorescent emission properties of 1 was studied by exciting the compound at 380 nm and also at 322 nm which were found to be the two λmax corresponding to absorptions of the molecule. Interestingly, the compound gave same type of emission spectra showing a maximum around 444 nm on exciting at these two different wavelengths, indicating that the molecule comes to the first excited state from the higher excited state by a fast non-radiative process before it exhibits singlet emission to come to the ground state. © 2007 Elsevier Masson SAS. All rights reserved. More »»
2007 Journal Article M. Padmanabhan, Joseph, K. C., Thirumurugan, A., Huang, X., Emge, T. J., and Li, J., “One-dimensional zig-zag type coordination polymers of Ni(II) and Cu(II) containing 1,3-benzenedicarboxylate and 1,3-diaminopropane: Structural, spectral and thermal studies”, Inorganica Chimica Acta, vol. 360, pp. 2583-2588, 2007.[Abstract]

Two coordination polymers [Ni(ipt)(dap)2]n (1) and [Cu(ipt)(dap)H2O]n · nH2O (2) with an overall one-dimensional arrangement and having isophthalate (ipt) as bridging moieties and chelating 1,3-diaminopropane (dap) as structure modulating units have been prepared and characterized by crystallographic, spectroscopic and thermo-analytical studies. Both have an overall one-dimensional zig-zag nature but with a distorted octahedral NiN4O2 chromophore for 1 and a distorted square pyramidal CuN2O3 chromophore for 2. Even though the ipt units are acting as bridging units through mono-dentatively coordinating carboxylate functions in both polymers, compound 1 has the carboxylate oxygen linkages at the trans positions, while in 2 the oxygen linkages occur at the cis positions leading to a different type of zig-zag arrangement. Relevant spectral and bonding parameters also could be evaluated for the compounds using UV-Vis and EPR spectra. Thermal stability and possible structural modifications on thermal treatment of the compounds were also investigated and the relevant thermodynamic and kinetic parameters evaluated from the thermal data. © 2007 Elsevier B.V. All rights reserved. More »»
2007 Journal Article T. James, M. Padmanabhan, Warrier, K. G. K., and Sugunan, S., “CuAl2O4 formation and its effect on α-Al2O3 phase evolution on calcination of metal ion doped boehmite xerogels”, Materials Chemistry and Physics, vol. 103, pp. 248 - 254, 2007.[Abstract]

The formation characteristics of CuAl2O4 from sol–gel boehmite doped with Cu2+ion and also the effect of dopants like Cu2+, Ti4+ and Ce4+ on calcination and concentration dependent structural evolution of α-Al2O3 from xerogels derived from boehmite sol are studied. The structural evolutions of various phases are studied by PXRD, FTIR, UV–vis (diffused reflectance) and \{EPR\} spectral techniques. Even though the formation temperature of α-Al2O3 from undoped boehmite is around 1200 °C, we observed significantly early and quantitative conversion of boehmite into α-Al2O3 along with the formation of CuAl2O4 spinel at 1000 °C in 4 and 8 mol.% Cu2+ ion doped samples owing to the nucleation effect and growth process initiated by the in situ generated spinel phase. However, no indication of such quantitative conversion in the case of 2% doped sample is seen presumably because of the retarding effect of transition aluminas on spinel formation. Temperature dependent phase evolution of CuAl2O4 spinel could be monitored by diffuse reflectance, \{EPR\} and PXRD, which show some interesting features associated with the change from CuO6 to CuO4 polyhedra. Dopants like Ti4+ and Ce4+ do not show any nucleation and facilitation effects in the formation of α-Al2O3 from boehmite xerogels. More »»
2006 Journal Article P. Padmaja, Warrier, K. G. K., M. Padmanabhan, Wunderlich, W., Berry, F. J., Mortimer, M., and Creamer, N. J., “Structural aspects and porosity features of nano-size high surface area alumina-silica mixed oxide catalyst generated through hybrid sol-gel route”, Materials Chemistry and Physics, vol. 95, pp. 56 - 61, 2006.[Abstract]

Alumina–silica mixed oxide nano-catalyst materials with compositions 83.6 wt.% Al2O3–16.4 wt.% SiO2 (3Al2O3·1SiO2), 71.82 wt.% Al2O3–28.18 wt.% SiO2 (3Al2O3·2SiO2), 62.84 wt.% Al2O3–37.16 wt.% SiO2 (3Al2O3·3SiO2) and 56.03 wt.% Al2O3–43.97 wt.% SiO2 (3Al2O3·4SiO2) have been prepared by a hybrid sol–gel technique using boehmite as the precursor for alumina and tetraethoxysilane as that for silica. The bonding characteristics and coordination features around Al and Si in the mixed oxide catalysts have been studied using \{FTIR\} and 27Al \{MAS\} \{NMR\} after calcination at 400 °C which is the temperature region where cross-condensation is seen to take place. A high \{BET\} specific surface area of 287 m2 g−1 is obtained for 3Al2O3·1SiO2 mixed oxide composition. The porosity features are further established by \{BET\} adsorption isotherms and pore size distribution analysis. The temperature-programmed desorption studies showed more surface active sites for the silica-rich composition, suggesting enhanced catalytic potential. The \{TEM\} features of the mixed oxides showed a homogeneous distribution of alumina and silica phases with particle sizes in the nano-range. The low silica-containing mixed oxide showed a needle-like morphology with a high aspect ratio of 1:50 and ∼10 nm particle size while the silica-rich composition had particle size in a wide range (∼20–75 nm).

More »»
2005 Journal Article M. Padmanabhan, Kumary, S. M., Huang, X., and Li, J., “Succinate bridged dimeric Cu(II) system containing sandwiched non-coordinating succinate dianion: Crystal structure, spectroscopic and thermal studies of [(phen)2Cu(μ-L)Cu(phen)2]L • 12.5H2O (H2L = succinic acid; Phen = 1,10-phenanthroline)”, Inorganica Chimica Acta, vol. 358, pp. 3537-3544, 2005.[Abstract]

A mixed ligand and dimeric CuII complex [(phen) 2Cu(μ-L)Cu(phen)2]L • 12.5H2O (H 2L = succinic acid) containing bridging succinate moiety and also non-coordinated succinate dianion was prepared from polymeric Cu(II) succinate by nucleophilic reaction with o-phenanthroline (phen) followed by depolymerization. The dimeric product was characterized by crystallographic, spectroscopic and thermoanalytical studies. The complex crystallizes in triclinic crystal system and is composed of succinate bridged [(phen) 2Cu(μ-L)Cu(phen)2]2+ complex cations, non-coordinated succinate anions and hydrogen bonded water molecules. Within the dimeric cationic unit, each of the Cu atoms is octahedrally coordinated by four N atoms of both phen ligands and both O atoms of a carboxylate moiety of the bridging succinate group in chelating form. Through intermolecular π-π stacking interactions, the complex cations form positively charged 2-D layers, between which the non-coordinating succinate anions and water molecules are sandwiched. Both the electronic and EPR studies indicate that the dimeric complex undergoes partial dissociation in solution state to exist in two structural forms. The kinetic and thermodynamic parameters involved in three stage thermal decompositions of the dimeric complex could also be evaluated using Coats-Redfern method. © 2005 Elsevier B.V. All rights reserved. More »»
2005 Journal Article R. G. George and M. Padmanabhan, “Studies on cobalt(II), nickel(II) and copper(II) derivatives of some new meso-aryl substituted octabromoporphyrins”, Polyhedron, vol. 24, pp. 679 - 684, 2005.[Abstract]

A series of Co(II), Ni(II) and Cu(II) derivatives of a variety of porphyrins with tolyl (H2TxTP) and naphthyl (H2NxTP) moieties as meso-substituents are synthesised and characterised. \{H2TxTP\} has the tolyl functions bonded to meso-carbons at the o-, m- or p-positions of the tolyl moieties while \{H2NxTP\} has naphthyl groups bonded through their α- or β-positions. Their octabromo derivatives (MTxOBP and MNxOBP) were also synthesised by electrophilic substitution at the β-pyrrole positions. Optical spectra showed that the Q bands remain almost unaltered for both tolyl and naphthyl derivatives of the nonbrominated porphyrins while the B bands of their naphthyl derivatives are seen to be more red-shifted than their tolyl analogues. Even though a similar trend based on the meso-substituents is observed among all \{MTxOBP\} and \{MNxOBP\} derivatives, a substantial red-shift is seen for all the bromoderivatives compared to their nonbrominated species \{MTxTP\} and MNxTP. The energy difference Δ ν ¯ associated with this red-shift of the Soret band is seen to be in the range 1700–2050 cm−1 for Co(II) and Ni(II) derivatives, the naphthyl derivatives always having higher values. Energy level reordering due to electron-withdrawing Br-substituents, distortion bringing about nonplanarity in the Ï€-framework resulting in HOMO–LUMO level changes and the mesomeric effect due to meso-aryl moieties can be considered to be the reasons for the observed spectral changes. The \{EPR\} spectra of the Cu(II) derivatives of bromoporphyrins have lower A ∥ Cu and A ⊥ Cu hyperfine values compared to their nonbrominated analogues, indicating enhanced delocalisation of electron spin to the octabromoporphyrinato moiety. An enhanced Cu–N σ-covalency is seen in the Cu(II)–bromoporphyrins, as evident from their lower α2 values. More »»
2004 Journal Article S. Chacko, Mathew, T., M. Padmanabhan, and Kuriakose, S., “Studies on polymer supported copper complexes: A comparison of EPR data”, Asian Journal of Chemistry, vol. 16, pp. 314-322, 2004.[Abstract]

2 per cent divinyl benzene (DVB) crosslinked polystyrene support was synthesized by suspension copolymerization technique and functionalized to get chloromethyl function. A series of ligands were anchored on to the polymer support by suitable chemical modifications. The ligands selected were Schiff bases, ethylene diamine and dithiocarbamates. The polymeric ligands were complexed with copper by simple chemical reactions. SS, NN, NO and OO donor sites form copper complexes with differing spectral and magnetic properties. The complexes were characterized by IR, UV-Vis and EPR studies. By varying copper environment, EPR parameters were measured and analyzed systematically. The structure, geometry and chemical properties of these complexes were studied from the spectral results. More »»
2004 Journal Article P. Padmaja, Pillai, P. K., Warrier, K. G. K., and M. Padmanabhan, “Adsorption Isotherm and Pore Characteristics of Nano Alumina Derived from Sol-Gel Boehmite”, Journal of Porous Materials, vol. 11, pp. 147-155, 2004.[Abstract]

This paper deals with a systematic investigation on the synthesis of aluminium oxide starting from mono hydroxy aluminium oxide (boehmite, (AlOOH)) which in turn is synthesized from aluminium nitrate. Boehmite on heating forms γ, transitional alumina and α-alumina phases in the temperature range 400–600, 800–1050 and 1050–1100°C respectively. Calculation from XRD, using Scherer equation shows that γ-alumina has crystallite size in the range 5–10 nm, while δ and θ-alumina are in the range 10–20 nm and α-alumina is about ∼33 nm. The textural features of aqueous sol-gel boehmite samples calcined at various temperatures were analyzed by specific surface area measurements and adsorption isotherm features. Maximum specific surface area of 266 m2/g is observed for the precursor calcined at 400°C and a minimum of 5 m2/g at 1100°C. Total pore volume is maximum for the precursor calcined at 600°C (0.2653 cm3/g). Average pore size ranges from ∼3 nm (400°C) to ∼11 nm (1100°C). The adsorption isotherms also show a change from Type IV to Type II with increase in temperature showing difference in surface properties. The information from t-plots, pore size distribution and cumulative pore volume data also indicates differences in porosity features of boehmite on calcination. The adsorption isotherm and pore size distribution analysis show maximum microporosity at 400°C, while maximum mesoporosity is observed at 600°C. At higher temperatures, porosity decreases, even though small fraction of pores in the mesopore range is still retained. At 1100°C, there is structural transformation from transitional to α-alumina, with very low specific surface area ∼5 m2/g and pores in the size range of 11 nm. The various data presented in this study will be useful in the synthesis of alumina with tailor made properties. More »»
2003 Journal Article R. G. George and M. Padmanabhan, “Studies on iron(III) and manganese(III) derivatives of new meso-aryl substituted and brominated porphyrins”, Transition Metal Chemistry, vol. 28, pp. 858-863, 2003.[Abstract]

A series of FeIII and MnIII porphyrins with various tolyl and naphthyl substituents at the meso positions, and their perbromoderivatives with Br substituents at the β-pyrrole positions, have been synthesised and investigated. As seen in the case of the free-base porphyrins, both FeIII and MnIII derivatives of the Br-substituted porphyrins also exhibit pronounced red-shifts in both B and Q bands compared to their nonbrominated analogues. This is attributed to the electron-withdrawing ability of eight Br substituents at β-pyrrole positions and is also due to distortion brought about in the π-framework by the bulky substituents including those at the meso positions. The naphthyl groups seem to be making mesomeric contributions for both nonbrominated and brominated porphyrins of these metal ions as is evident from the higher wavelength absorption of the B band as compared to the tolyl derivatives. While the meso-substituent do not exhibit any isomer dependent change on the electronic properties of FeIII porphyrins, they show a noticeable effect in the MnIII derivatives. During the metallation of meso-tetratolylporphyrins by FeIII ions μ-oxo dimeric compounds are formed, while the naphthyl porphyrins and the bromoderivatives do not form such dimeric species. The presence of bulky groups at the meso positions and heavy bromines on the β-pyrrole positions can be considered to prevent the formation of catalytically inert μ-oxo dimers. More »»
2003 Journal Article R. G. George and M. Padmanabhan, “Studies on some new meso-aryl substituted octabromo-porphyrins and their Zn(II) derivatives”, Polyhedron, vol. 22, pp. 3145-3154, 2003.[Abstract]

A series of porphyrins with various tolyl (H2TTHP) and naphthyl substituents (H2TNHP) at the meso-positions, their octabromoderivatives (H2TTBP and H2TNBP) with Br substituents at β-pyrrole positions and also their Zn(II) derivatives have been synthesised and characterised by 1H NMR, electronic, fluorescence and electrochemical studies. These have the meso-carbons bonded to tolyl moieties at ortho-, meta- and para-positions of the tolyl groups and at the α- or β-position of the naphthyl group. For the octabromoporphyrins, pronounced deshielding of NH protons and a moderate shift of meso-aryl protons to a lower δ value are observed compared to their nonbrominated species. The electronic spectra of ZnTTHP and ZnTNHP have almost the same B and Q bands while the B band of their free-base analogues have H 2TNHP absorbing at a higher wavelength than H2TTHP. All the octabromoderivatives exhibit a pronounced red shift for both B and Q bands (compared to their nonbrominated forms) and show meso-substituent dependent change in both free-base and metallated forms. The above observations are interpreted in terms of moderate conjugative interaction of the aryl substituent with the π framework and also in terms of energy level reordering which alters the HOMO-LUMO gap. Consistent with the absorption spectral data the emission bands of all the bromoporphyrins were also seen to be red shifted considerably. Significant decrement in quantum yield (φf) was observed for the bromocompounds. While the φf of nonbrominated porphyrins is seen to be higher than their Zn(II) derivatives the reverse order is observed for the bromoderivatives. The ability of the Zn2+ ion to make the bromoporphyrins resistant to distortion by bridging the central cavity can be attributed as the cause for this interesting observation. Cyclic voltammetric studies exhibit characteristic quasi-reversible/irreversible oxidation-reduction features for all the free-bases and Zn(II) derivatives. The bromoderivatives on the other hand manifest marginally harder oxidation and very easy reduction features. The data are interpreted in terms of electron withdrawing ability of Br atoms and to reordering of HOMO and LUMO levels due to distortion in the porphyrin ring. © 2003 Elsevier Ltd. All rights reserved. More »»
2003 Journal Article R. G. George and M. Padmanabhan, “Solvent effects on some new meso-aryl substituted octabromoporphyrins”, Proceedings of the Indian Academy of Sciences: Chemical Sciences, vol. 115, pp. 263-271, 2003.[Abstract]

A series of porphyrins with tolyl and naphthyl substituents at the meso positions, their octabromoderivatives (OBP) with Br substituents at β-pyrrole positions are synthesised and characterised by chemical analysis. 1H NMR and electronic spectral studies. It is seen that all the OBPs exhibit pronounced red shifts in both the Soret and Q bands of their electronic spectra compared to their nonbrominated form in various polar and nonpolar solvents, the energy difference Δv̄ being in the range 2300-2700 cm-1. The high energy B band of naphthyl porphyrins (both brominated and nonbrominated) are found to be more red-shifted than that of tolyl porphyrins, owing to the noticeable mesomeric effect of the naphthyl groups. Detailed spectral studies reveal that while none of the nonbrominated porphyrin show solvent-dependent change in their B and Q bands, all the OBPs manifest significant shifts depending on the nature of solvents. Solvent-solute interaction can be considered to be of strong dipole-dipole nature for OBPs with polar solvents and of π-π type with aromatic non-polar solvents. In the brominated form we find two categories of porphyrins exhibiting distinctly different absorption phenomena in aromatic solvents. The OBPs having meso-groups not shielding the porphyrin π-framework exhibit additional absorption peaks (split Soret peaks and broadened Q bands) in some aromatic solvents. This could be explained in terms of π-π type donor-acceptor (DA) complex formation between such bromoporphyrins (acceptor) and the aromatic solvent molecules (donor) that is not possible for OBPs that have bulky meso groups that block the approach of aromatic solvent molecules close to the porphyrin framework. More »»
2003 Journal Article J. J. Inbaraj, Vinodu, M. V., Gandhidasan, R., Murugesan, R., and M. Padmanabhan, “Photosensitizing properties of ionic porphyrins immobilized on functionalized solid polystyrene support”, Journal of Applied Polymer Science, vol. 89, pp. 3925-3930, 2003.[Abstract]

The photogeneration of singlet oxygen (1O2) by tetrasodium salt of meso-tetrakis(4-sulfonatophenyl)porphyrins (H 2TPPS) and some of its metal complexes (MTPPS; M = Cd2-, Zn2+), immobilized on cationically functionalized polystyrene (PS) beads, was studied. The generation of 1O2 was monitored by a N,N-dimethyl-4-nitrosoaniline (RNO) bleaching assay. The rate of RNO bleaching was seen to be retarded in the presence of DABCO, a specific 1O2 scavanger, providing evidence for the involvement of 1O2 as an active intermediate. The relative efficiencies of the generation of 1O2, with respect to immobilized rose bengal (PS-RB), by different polymer-supported porphyrins, were determined to be 0.29, 0.27, and 0.16 for PS-H2TPPS, PS-ZnTPPS, and PS-CdTPPS, respectively. Binding of porphyrins to a polymer has been found to decrease the efficiency of the 1O2 generation, which could be attributed to the structural deformation of the appended porphyrins. © 2003 Wiley Periodicals, Inc. More »»
2003 Journal Article S. Chacko, Mathew, Tad, M. Padmanabhan, and Kuriakose, S., “Generation and characterization of new oxovanadium complexes on polymer support”, Asian Journal of Chemistry, vol. 15, pp. 825-832, 2003.[Abstract]

2 Per cent divinyl benzene (DVB) crosslinked polystyrene support was synthesised and functionalised to get chloromethyl polystyrene. Polymeric ligands were prepared by anchoring ligand systems like Schiff base, ethylene diamine and dithiocarbamate on to the polymer backbone. A series of oxovanadium complexes were generated on the polymer support by polymer-analogous complexation reactions. Polymeric oxovanadium complexes containing S2O2, N2O2 and NO3 chromophores were analysed by chemical and spectroscopic methods. Important spectral results from UV-Vis, IR and EPR analysis are discussed in detail. The results best explain the bonding pattern and stereochemistry of the complexes. More »»
2001 Journal Article M. Vinodu and M. Padmanabhan, “Peroxidase-like catalytic activities of ionic metalloporphyrins supported on functionalised polystyrene surface”, Proceedings of the Indian Academy of Sciences: Chemical Sciences, vol. 113, pp. 1-9, 2001.[Abstract]

{Metalloderivatives of anionic tetrasulphonated tetraphenylporphyrin (MTPPS More »»
2001 Journal Article M. V. Vinodu and M. Padmanabhan, “Electronic effect of polymeric environments on metalloporphyrins”, Journal of Polymer Science, Part A: Polymer Chemistry, vol. 39, pp. 326-334, 2001.[Abstract]

Electronic modulations brought about on ionic metalloporphyrins by various polymeric environments were investigated in detail with spectral analysis. The porphyrins employed were metalloderivatives of anionic p-sulfonated tetraphenylporphyrins [MTPPS; M = Cu(II), Zn(II), Ag(II), and Cd(II)]. The polymer system chosen involved poly(4-vinylpyridine) (PVP), crosslinked and linear polystyrenes partially chloromethylated and quaternized (PS and PS′), and polyethylene glycol (PEG). These were expected to interact with MTPPS through a coordinate bond on its central metal atom (PVP), through Coulombic attraction (PS and PS′), or through ion-dipolar interaction (PEG). Significant changes in the electronic spectra (redshifts in both B and Q bands) were seen in polymer-incorporated MTPPS in comparison with free MTPPS. For a given metalloporphyrin, the order of the spectral shifts was always MTPPSZn>Ag>Cu. This is explained in terms of the molecular distortions and associated changes in the metalloporphyrin orbital overlap and the charge delocalization from the peripheral substituents or coordinating ligand functions to the porphyrin π framework. More »»
2001 Journal Article M. V. Vinodu and M. Padmanabhan, “Ionically bound metalloporphyrin pairs on solid polymer support”, Journal of Porphyrins and Phthalocyanines, vol. 5, pp. 763-766, 2001.[Abstract]

The present work demonstrates a simple and elegant strategy by which synthetically simple porphyrins are grafted on solid polymer support to generate porphyrin pairs held together by strong coulombic forces. Metalloporphyrins of tetra(4-pyridyl)porphyrins (MTPyP) were reacted with chloromethylated polystyrene (PS) beads to get covalently bound monocationic porphyrins on the polymer support (PS-MTPyP+). These were then converted to their tetracationic species (PS-MTMe3PyP4+) by exhaustive quaternisation, using CH3I. These polymer-grafted cationic porphyrins were made to react with tetraanionic p-sulphonated phenylporphyrins (MTPPS4-) in aqueous conditions. Analysis showed that the PS-MTMe3PyP4+ take up MTPPS4- in exactly 1:1 stoichiometry to form strongly bound (ionically) porphyrin pairs. A variety of homo- and hetero-porphyrin pairs involving central metal ions like Mn, Co, Cu, Zn and Ag and also free-base porphyrins are generated by this strategy. Copyright © 2001 John Wiley & Sons, Ltd. More »»
2000 Journal Article T. Mathew, M. Padmanabhan, and Kuriakose, S., “Studies on polymer-appended free base porphyrins with ether linkage and their copper complexes”, Indian Journal of Chemistry - Section B Organic and Medicinal Chemistry, vol. 39, pp. 414-418, 2000.[Abstract]

Monohydroxy- and tetrahydroxyporphyrins have been anchored on crosslinked polystyrene matrices through ether linkage. Ortho, meta and para substituted polymeric porphyrins have been synthesised from chloromethyl polystyrene and suitably substituted porphyrins and the products characterised by spectral studies. The interesting features of the electronic spectra of polymer anchored porphyrins like split soret bands are explained by the orientational variation in ortho-, meta- and para-isomers and the effect of polymer-porphyrin interaction on the electronic levels of porphyrin macrocycle. The copper complexes of these polymer-bound porphyrins are synthesised and analysed spectroscopically. Electronic and ESR spectra show interesting results and these are explained based on the electronic modification of porphyrin systems on a rigid macromolecular backbone. More »»
1998 Journal Article M. V. Vinodu and M. Padmanabhan, “Studies on a catalase model system based on immobilised metalloporphyrins on modified solid polystyrene support”, Proceedings of the Indian Academy of Sciences: Chemical Sciences, vol. 110, pp. 461-470, 1998.[Abstract]

Metalloporphyrins immobilised on solid polymer supports are developed as efficient model systems for catalyse enzyme, which dismutate hydrogen peroxide in many living organisms, saving them from several harmful oxidative processes. The metalloporphyrins employed are Mn(III), Fe(III) and Co(III) derivatives of anionic tetrasulphonated tetraphenylporphyrins (H2TPPS). The polymer support used was divinylbenzene crosslinked polystyrene (in bead form) which was first surface functionalised to chloromethyl derivative and then to N-alkyl pyridinium derivatives (PS). The negatively charged MTPPS were then appended on to the polymer support by ion exchange method. The catalytic efficiency of these immobilised MTPPS was found to be far superior to other supported systems reported earlier. The relative efficiency of the three supported metalloporphyrin systems was studied and compared in varying pH and temperature conditions. In acidic pH, the order of efficiency of the metalloderivatives was Fe(III) > Mn(III) > Co(III) while in basic pH, the order changed to Mn(III) K Co(III) > Fe(III). The maximum efficiency was found to be around pH 10-0 in all the cases. While the Fe(III) derivatives showed greater sensitivity to temperature, the Mn(III), on the contrary, showed the least sensitivity. The catalytic efficiency of the immobilised systems was found to be retained even after repeated use of the catalysts indicating a high degree of recyclability. © Indian Academy of Sciences. More »»
1996 Journal Article T. Mathew and M. Padmanabhan, “Studies on polymer supported metalloporphyrins with modified electronic properties”, Proceedings of the Indian Academy of Sciences - Chemical Sciences, vol. 108, p. 341, 1996.
1996 Journal Article T. Mathew, Kuriakose, S., and M. Padmanabhan, “Catalytic properties of cobalt(II) porphyrins supported on styrene-divinylbenzene copolymer”, Journal of Applied Polymer Science, vol. 59, pp. 23-27, 1996.[Abstract]

Polymeric pyridinium chloride was synthesized by treating pyridine with 2% divinylbenzene (DVB)-crosslinked chloromethyl polystyrene. Sodium 5,10,15,20-tetrakis(4-sulfophenyl)porphyrin was synthesized and appended on the above polymer through an ionic linkage. Cobalt(II) complex of the polymeric porphyrin was synthesized and characterized chemically and spectroscopically. This complex was employed as catalyst for the oxidation of dithiocarbamates to thiuram disulfide. Electronic and ESR spectra of the complex were analyzed before and after catalysis. pH dependence of catalytic reactions was also studied. These studies provide evidence for the catalytic ability of the polymeric cobalt(II) porphyrin system. A mechanism for the catalytic reaction is suggested on the basis of the above results. © 1996 John Wiley & Sons, Inc. More »»
Publication Type: Book Chapter
Year of Publication Publication Type Title
2016 Book Chapter M. Padmanabhan, Sasidharan, S., Rajesh, K., Nambiar, S., Nair, B. N., Warrier, K. G. K., and Hareesh, U. S., “Sol-Gel Lanthanum Phosphate: A Versatile Ceramic Material for Diverse Functional Applications’”, Germany: Springer Publishers, 2016.
Publication Type: Conference Paper
Year of Publication Publication Type Title
2016 Conference Paper M. Padmanabhan, K., V. K., Andrews, A. P., and Pillai, Z. S., “Novel light-emitting and magnetically active ‘metallogels’ exhibiting unprecedented solvent encapsulation properties”, in International Conference on Materials Science and Technology, 2016.
2016 Conference Paper M. Padmanabhan, K., V. K., Alex, A. P., and Pillai, Z. S., “Tuning of of pyranine (HPTS) by lanthanides - synthesis, crystal structure and emission properties of of pyranine (HPTS) by lanthanides - synthesis, crystal structure and emission”, in International Conference on Materials Science and Technology, 2016.
2016 Conference Paper M. Padmanabhan, R., D. Mohan, K., V. K., Andrews, A. P., and Pillai, Z. S., “Structurally diverse and magnetically active new crystalline metal organic framework (MOF) materials from ‘metallogels”, in International Conference on Materials Science and Technology, 2016.
2016 Conference Paper M. Padmanabhan, Baby, S., and Thomas, S. P., “Reversible structural, optical and magnetic switching in crystalline 1-dimensional inorganic-organic hybrid polymers induced by H2O”, in International Conference on Materials Science and Technology, 2016.
2015 Conference Paper M. Padmanabhan, K, V. K., Sudha, J. D., and Pillai, Z. S., “Role of functional ‘arms’ in the formation of fluorescent rare-earth based metal-organic framework gels (MOFGs), ”, in National Conference on Materials Science and Technology, Trivandrum, 2015.
2015 Conference Paper M. Padmanabhan, K, V. K., Sudha, J. D., and Pillai, Z. S., “A Lanthanide based photoluminescent metal-organic coordination polymer gels”, in National Conference on Materials Science and Technology, Trivandrum, 2015.
2010 Conference Paper J. Li, M. Padmanabhan, Zhao, Y., and Wu, H., “Tuning structures and hydrogen adsorption properties of microporous metal organicframework (MMOF) materials”, in ACS National Meeting Book of Abstracts, Boston, MA, 2010.[Abstract]

Developing alternative and clean energy sources/carriers to replace fossil fuels has become one of the most pressing areas of research in the recent years because of the urgent need to reduce the level of greenhouse gas emission and global warming. Being the most abundant element in the universe, hydrogen has great potential to become one of the dominant energy carriers on earth. In addition, the energy generation reaction involving hydrogen gives water, an environmentally clean species, as the sole byproduct, which is most desirable. However, adequate storage of hydrogen remains a key issue that must be addressed if hydrogen economy is to be realized. Intensive search for efficient hydrogen storage materials has been made but none of the existing methods is good enough yet for commercialization. Microporous metal organic frameworks are a new type of adsorbent materials that are currently under extensive investigations. As a subset of the general family of metal organic frameworks (MOFs), these materials contain very small pores with pore dimensions less than twenty and often only several angstroms. They exhibit similar sorption properties to other porous materials characteristic of physisorption, including carbonaceous, silica and alumina, but demonstrate some apparent advantageous features over these systems. For example, the MMOFs incorporate metal centers that interact with adsorbed hydrogen molecules more strongly. They contain perfectly ordered pores that allow hydrogen to access the interior space more effectively. The synthesis typically involves simple one-pot reactions, are highly reproducible and cost effective. Furthermore, the crystal structures and pore characteristics of MMOFs can be systematically and deliberately modified to improve hydrogen uptake. In this presentation, we will describe our recent progress in rational design, synthesis, structure modification of new MMOF materials, and discuss our strategy and approach to enhance H2-MMOF interactions and to maximize hydrogen uptakes in these materials by tuning and optimizing their crystal structures and pore properties. More »»
Publication Type: Conference Proceedings
Year of Publication Publication Type Title
2016 Conference Proceedings A. R, K, V. K., R, D. Mohan, Alex, A. P., Pillai, Z. S., and M. Padmanabhan, “Novel hetero-metal cluster MOFs through ‘metallogel’ route”, National Conference on Materials Science and Technology. IIST, ISRO, Trivandrum., 2016.
2016 Conference Proceedings A. J. M. Nair, R, D. Mohan, K., V. K., Alex, A. P., Arjun, R. C. Nath U., Pillai, Z. S., and M. Padmanabhan, “Synthesis, crystal structure, spectral and super-paramagnetic properties of a novel Gd(S=7/2) - Cu(S=1/2) MOF formed in situ by a facile ‘metallogel’ route”, National Conference on Materials Science and Technology. IIST, ISRO, Trivandrum, 2016.
2016 Conference Proceedings S. P. K., Thomas, S., M. Padmanabhan, and Sreekala, M. S., “Effect of Graphene Oxide Reduced by Potato Starch on the Mechanical Properties of Phenol Formaldehyde Resole Resin Polymer Nanocomposites”, National Conference on Materials Science and Technology. IIST, ISRO, Trivandrum., 2016.
2016 Conference Proceedings A. M. K., M. Padmanabhan, Thomas, S., and Mathew, L. P., “Thermal, Dielectric and Wetting Properties of Polytrimethylene Terephthalate (PTT)/Multi Walled Carbon Nanotube (MWCNT) Nanocomposites. ”, National Conference on Materials Science and Technology. IIST, ISRO, Trivandrum., 2016.
2016 Conference Proceedings H. D. V., K, V. K., Alex, A. P., M, G. T., Pillai, Z. S., Reddy, M. L. P., and M. Padmanabhan, “Visible and NIR light emitting novel Nd-pyranine coordination polymer- synthesis, crystal structure, packing features and fluorescence properties ”, National Conference on Materials Science and Technology. IIST, ISRO, Trivandrum, 2016.
2016 Conference Proceedings D. Mohan R, K, V. K., Andrews, A. P., K, A., Arjun, U., Pillai, Z. S., Nath, R. C., and M. Padmanabhan, “Structurally diverse and magnetically active new crystalline metal organic framework (MOF) materials from 'metallogels'”, The Second International Conference on Materials Science and Technology (ICMST2016). St. Thomas College, Palai, Kerala , 2016.

Invited Talks

  1. ‘Perspectives in Organometallics’ (National Seminar on Emerging Trends in Chemistry’, St. Thomas College, Moolamattom, December, 2015) - Invited Talk.
  2. ‘Structure and Bonding Aspects in Chemistry’ (National Seminar on ‘Emerging Trends in Chemistry’, St. Thomas College, Moolamattom, December, 2015) - Invited Talk.
  3. ‘Structure Predictions of Complex Organometallic Compounds’, (Colloquium Series Lecture - I, Mahatma Gandhi College, Trivandrum, January 30, 2016) - Invited Talk.
  4. ‘Isolobal Concept in Chemistry’ (Colloquium Series Lecture -II, Mahatma Gandhi College, Trivandrum, January 30, 2016) - Invited Talk.
  5. Role of functional ‘arms’ in the formation of fluorescent rare-earth based metal-organic framework gels (MOFGs), National Conference on Materials Science and Technology, IIST, Trivandrum, July 6-8 (2015) (Invited Plenary Lecture, accepted). 
Faculty Details

Qualification:

Designation: 
Faculty Email: 
padmanabhanm@am.amrita.edu