Qualification: 
Ph.D, MSc
gopalk@am.amrita.edu

Dr. Gopal K. currently serves as Assistant Professor (Sl.Gr) in the Department of Chemistry, School of Arts and Science, Amritapuri Campus. He completed his Ph.D. in 2008 from Indian Institute of Technology – Kanpur in the area of main-group organometallics. Prior to his appointment at Amritapuri Campus, he worked as Marie-Curie Post-doctoral Fellow at The University of Manchester, UK (for 2 years), DST – Young Scientist at Indian Institute of Technology – Bombay (for 2 years) and Assistant Professor at Central University of Rajasthan (for 3 years).

His research interest include in the area of main-group and transition metal chemistry of catalytically and magnetically interesting metallo-molecular systems and semiconductor nanostructures.

Publications

Publication Type: Journal Article

Year of Publication Publication Type Title

2017

Journal Article

R. S. Pathare, Sharma, S., Dr. Gopal K., Sawant, D. M., and Pardasani, R. T., “Palladium-catalyzed Convenient One-pot Synthesis of Multi-substituted 2-pyrones via Transesterification and Alkenylation of Enynoates”, Tetrahedron Letters, vol. 58, pp. 1387 - 1389, 2017.[Abstract]


An efficient one-pot protocol for the synthesis of multi-substituted 2-pyrone derivatives from internal alkynes and unactivated alkenes is reported. The methodology involves difunctionalization of internal alkynes by using Pd(II) as a catalyst alongwith X-Phos as ligand via 6-endo transesterification and subsequent alkenylation pathway. Notable features include simple and easily available starting materials, including a range of unactivated alkenes, reduced synthetic steps and mild reaction conditions with high efficiency.

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2016

Journal Article

A. J. Ansari, Sharma, S., Pathare, R. S., Dr. Gopal K., Sawant, D. M., and Pardasani, R. T., “Solvent–free Multicomponent Synthesis of Biologically–active Fused–imidazo Heterocycles Catalyzed by Reusable Yb(OTf)3 Under Microwave Irradiation”, ChemistrySelect, vol. 1, pp. 1016–1021, 2016.[Abstract]


A rapid, efficient and solvent-free – green – protocol for Groebke–Bienaymé–Blackburn reaction (G−B-B reaction) for the synthesis of fused-imidazo heterocycles has been developed. The methodology reported here involves multi-component reaction (MCR) catalyzed by reusable Yb(OTf)3 (a mild and water-compatible Lewis acid) under microwave irradiation which allows fast and efficient preparation of the title compounds in excellent yield. The salient features of our protocol are solvent-free, low catalyst loading (2.5–0.1 mol%) with good turnover number (TON: 890) and turnover frequency (TOF: 178/min), less reaction time (5 min), no dependency over specialized purification (by either column chromatography or recrystallization) and very high isolated yield (95–99 %) with excellent green chemistry metrics (E-factor: 0.071 and Mass Intensity: 1.071). The water compatibility of the catalyst Yb(OTf)3 has been exploited for its efficient recovery through water washings. In addition, the other exciting milestones of the protocol are catalyst and workup solvent recycling, excellent conversion with notorious substrates such as enolizable aldehyde or isonitrile bearing reactive substituent, very efficient at higher scale (50 mmol) and easy to couple with other methods (one-pot two-step cyclization: G−B-B reaction and Ullmann-type coupling).

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2016

Journal Article

S. Sharma, Pathare, R. S., Maurya, A. K., Dr. Gopal K., Roy, T. Kanchan, Sawant, D. M., and Pardasani, R. T., “Ruthenium Catalyzed Intramolecular C–S Coupling Reactions: Synthetic Scope and Mechanistic Insight”, Organic Letters, vol. 18, pp. 356-359, 2016.[Abstract]


A ruthenium catalyzed intramolecular C–S coupling reaction of N-arylthioureas for the synthesis of 2-aminobenzothiazoles has been developed. Kinetic, isotope labeling, and computational studies reveal the involvement of an electrophilic ruthenation pathway instead of a direct C–H activation. Stereoelectronic effect of meta-substituents on the N-arylthiourea dictates the final regioselective outcome of the reaction.

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2014

Journal Article

Dr. Gopal K., Kundu, S., Metre, R. K., and Chandrasekhar, V., “Ambient Temperature Sn–C Bond Cleavage Reaction Involving the Sn-n-butyl Group. Weak F···F Interactions in the Solid State Structure of [nBu2SnO2C–C6H4-4-CF32O]2”, Zeitschrift für anorganische und allgemeine Chemie, vol. 640, pp. 1147–1151, 2014.[Abstract]


The reaction of bis(tri-n-butyltin)oxide, [nBu3Sn]2O, with HO2C–C6H4–4-CF3 (RfTol-CO2H) affords a coordination polymer [nBu3SnO2C–RfTol]n (1). 1 undergoes hydrolysis in the presence of atmospheric moisture, at room temperature, resulting in the formation of the diorgano stannoxane [{nBu2SnO2C–RfTol}2O]2 (2). The transformation of 1 to 2 is accompanied by a Sn–C bond cleavage reaction. Formation of 2 also occurs in a direct reaction, involving [nBu3Sn]2O and RfTol–CO2H in the presence of water. 2 can also be prepared in a 1:1 reaction of di-n-butyltin oxide, [nBu2SnO]n with RfTol–CO2H. The conversion of 2 from 1 was monitored by 119Sn NMR spectroscopy over a period of eight days. The molecular structure of 2 reveals a tetranuclear assembly consisting of two pairs of structurally distinct six-coordinate tin atoms. Extensive hydrogen-bonding interactions (C-H···O, C-H···F) and weak F···F interactions involving organo-fluorine atoms in the crystal structure result in the formation of a three-dimensional supramolecular architecture for 2.

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2014

Journal Article

V. Chandrasekhar, Goura, J., Dr. Gopal K., Liu, J., and Goddard, P., “Synthesis, Structure and Magnetism of the mixed-valent phosphonate cage, [MnIIMnIII12(μ4-O)6(μ-OH)6(O3P–t-Bu)10(OH2)2(DMF)4]·[2MeOH·4DMF]”, Polyhedron, vol. 72, pp. 35 - 42, 2014.[Abstract]


Abstract The reaction of MnCl2·4H2O with t-BuPO3H2 in the presence of triethylamine afforded the tridecanuclear cage, [MnIIMnIII12(μ4-O)6(μ-OH)6(O3P–t-Bu)10(OH2)2(DMF)4]·[2MeOH·4DMF] (1). The structural analysis of 1 reveals that it is a mixed-valent complex containing a [MnIIMnIII12(μ4-O)6] core. The centre of the core is occupied by a MnII ion which is surrounded by 12 MnIII ions. The latter are connected to each other by six μ-OH− and 10 t-BuPO32− ligands. The vacant coordination sites of six MnIII ions situated in the periphery are occupied by four \{DMF\} and two water molecules. Magnetic studies on 1 reveal a frequency-dependent response which is characteristic of single-molecule magnets.

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2013

Journal Article

K. Ramasamy, Kuznetsov, V. L., Dr. Gopal K., Malik, M. A., Raftery, J., Edwards, P. P., and O’Brien, P., “Organotin Dithiocarbamates: Single-Source Precursors for Tin Sulfide Thin Films by Aerosol-Assisted Chemical Vapor Deposition (AACVD)”, Chemistry of Materials, vol. 25, pp. 266-276, 2013.[Abstract]


A series of diorganotin complexes of dithiocarbamates [Sn(C4H9)2(S2CN(RR′)2)2] (R, R′ = ethyl (1); R = methyl, R′ = butyl (2); R, R′ = butyl (3); R = methyl, R′ = hexyl (4); and [Sn(C6H5)2(S2CN(RR′)2)2] (R, R′ = ethyl (5); R = methyl, R′ = butyl (6); R, R′ = butyl (7); R = methyl, R′ = hexyl (8) were synthesized. Single-crystal X-ray structures of 2, 3, and 8 were determined. Thermogravimetric analysis (TGA) showed single-step decomposition for the complexes 1, 3, and 5–8, and double-step decomposition for the complexes 2 and 4 between 195 °C and 325 °C. Complexes 1–4 were used as single-source precursors for the deposition of SnS thin films by aerosol-assisted chemical vapor deposition (AACVD) at temperatures from 400 °C to 530 °C. Orthorhombic SnS thin films were deposited from all four complexes at all deposition temperatures. The films were characterized by UV–vis spectroscopy, powder X-ray diffraction (p-XRD), Raman spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and also electrical resistivity measurements.

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2013

Journal Article

V. Chandrasekhar, Kundu, S., Kumar, J., Verma, S., Dr. Gopal K., Chaturbedi, A., and Subramaniam, K., “Supramolecular Signatures of Adenine-Containing Organostannoxane Assemblies”, Crystal Growth & Design, vol. 13, pp. 1665-1675, 2013.[Abstract]


The reactions of 3-(N9-adeninyl) propanoic acid (LH) with various di- and triorganotin oxides have been investigated. Thus, the reaction of di-tert-butyltin oxide (t-Bu2SnO)3 in a 3:1 ratio afforded the dinuclear derivative [t-Bu2Sn(μ-OH)L]2·7H2O (1). A similar reaction involving bis(tri-n-butyltin)oxide, (n-Bu3Sn)2O, in a 2:1 ratio afforded the one-dimensional (1D) coordination polymer [n-Bu3SnL·0.33H2O]n (2). Similarly the reaction with (n-Bu2SnO)n in a 2:1 ratio afforded the tetranuclear [{n-Bu2Sn}2(μ3-O)(μ-OH)L]2 (3). On the other hand, a similar reaction in a 1:1 ratio also gave the tetranuclear product [{n-Bu2Sn}2(μ3-O)L2]2 (4). The molecular structure of 1reveals a central dinuclear Sn2O2 motif where the two tin centers are bridged by two μ-OH groups. Each tin is bound with a monodentate carboxylate group; the C═O unit of these carboxylates is involved in an intramolecular hydrogen bonding with the bridging OH unit. The supramolecular structure of 1 reveals the formation of a 1D zigzag chain mediated by intermolecular hydrogen bonding interaction through the Watson-Crick or the Hoogsteen faces. 2 is a 1D coordination polymer formed by the successive bridging of triorganotin units by the carboxylate ligand L. The supramolecular structure of 2 reveals that two 1D coordination polymers interact to generate novel adenine homotrimers formed as a result of alternating Watson-Crick–Watson-Crick and Hoogsteen–Watson-Crick interactions. The molecular structures of 3 and 4 reveal them to be tetranuclear possessing a ladder-like structure. The essential difference between their molecular structures is that in 4 there are four carboxylate ligands, while in 3 there are only two. Both of these complexes reveal intramolecular and intermolecular hydrogen bonding and π···π stacking interactions. The nematicidal activity of 1–3 was examined against Caenorhabditis elegans. Compound 2 was found to be highly active, effecting a high mortality even at very low concentrations such as 25 or 10 ppm.

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2012

Journal Article

V. Chandrasekhar, Nagarajan, L., Hossain, S., Dr. Gopal K., Ghosh, S., and Verma, S., “Multicomponent Assembly of Anionic and Neutral Decanuclear Copper(II) Phosphonate Cages”, Inorganic Chemistry, vol. 51, pp. 5605-5616, 2012.[Abstract]


{ A multicomponent synthetic strategy involving copper(II) ions, tert-butylphosphonic acid (t-BuPO3H2) and 3-substituted pyrazole ligands has been adopted for the synthesis of soluble molecular copper(II) phosphonates. The use of six different 3-substituted pyrazoles, 3-R-PzH [R = H, Me, CF3, Ph, 2-pyridyl (2-Py), and 2-methoxyphenyl (2-MeO-C6H4)] as ancillary ligands afforded nine different decanuclear cages, [Cu5(μ3-OH)2(O3P-t-Bu)3(3-R-Pz)2(X)2]2·(Y) where R = H

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2012

Journal Article

V. Chandrasekhar, Singh, P., Dr. Gopal K., and Steiner, A., “Trapping Dimethyltin Cations by Bipyridine-N,N′-Dioxide Ligands”, Zeitschrift für anorganische und allgemeine Chemie, vol. 638, pp. 1716–1722, 2012.[Abstract]


N,N′-dioxide ligands such as 2, 2′-bipyridine-N,N-dioxide (BPDO-I) and 4, 4′-bipyridine-N,N-dioxide (BPDO-II) were used to trap the hydrated dimethyltin cations under controlled hydrolysis. The use of the chelating ligand BPDO-I leads to the isolation of the discrete monocation [Me2Sn(BPDO-I)(OH2)(NO3)]+[NO3]– (2), whereas the linear ligand BPDO-II directs the construction of cationic polymers, [{Me2Sn(OH2)2(μ-BPDO-II)}2+{NO3–}2·2H2O]n (3·2H2O) and [{Me2Sn(μ-OH)(BPDO-II)}22+{NO3–}2·H2O]n (4·H2O) under different reaction conditions.

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2011

Journal Article

V. Chandrasekhar, Pandey, M. D., Dr. Gopal K., and Azhakar, R., “Assembly of a dinuclear silver complex containing an Ag 2 S 2 motif from a phosphorus-supported trishydrazone ligand. P [double bond, length as m-dash] S→ Ag I coordination”, Dalton Transactions, vol. 40, pp. 7873–7878, 2011.[Abstract]


The reaction of the phosphorus trihydrazide, (S)P[N(Me)-NH2]3 (1) with quinoline-2-carboxaldehyde (C9H6N-2-CHO) in a 1 : 3 ratio afforded a trishydrazone, (S)P[N(Me)-N[double bond, length as m-dash]CH-2-C9H6N]3 (2). Crystals of 2 were grown in three different solvent media affording an unsolvated (2, monoclinic, P21/n) and two solvated (2·3H2O, trigonal, R3 and 2·2CH3OH, triclinic, P[1 with combining macron]) crystal forms. Each of these, while possessing an essentially similar molecular structure, adopt different crystal packing giving rise to supramolecular structures mediated by a variety of weak interactions: O–H–N, O–H–O, C–H–N, C–H–O, C–H–S, C–H–π, π–π, N–π and S–π. The reaction of 2 with Ag(ClO4)2·6H2O in methanol afforded a dinuclear cationic cage [Ag{(S)P[N(Me)-N[double bond, length as m-dash]CH-2-C9H6N]3}·ClO4]2 (3). The molecular structure of 3 reveals a dimeric structure consisting of two AgI ions that are held together by two ligands. Only two arms of the tris hydrazone ligand are involved in coordination while an unprecedented P[double bond, length as m-dash]S→AgI coordination is seen. This results in the formation of an Ag2S2 dimer that is encapsulated by two trishydrazone ligands. Both compounds 2 and 3 are photoluminescent.

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2011

Journal Article

V. Chandrasekhar, Senapati, T., Dey, A., Hossain, S., and Dr. Gopal K., “Carbophosphazene-Based Multisite Coordination Ligands: Metalation Studies on the Pyridyloxy Carbophosphazene, [NC(NMe2)]2[NP(p-OC5H4N)2]”, Crystal Growth & Design, vol. 11, pp. 1512-1519, 2011.[Abstract]


The pyridyloxycarbophosphazene, [NC(NMe2)]2[NP(p-OC5H4N)2] (L), reacted with Cd(OAc)2·4H2O to afford a rail-road-like double-strand coordination polymer, [{Cd(CH3COO)2(L)}(CH3OH)(H2O)2]n (1). The crystal structure of 1 reveals that L functions as a bridging ligand to link successive cadmium atoms. Two such parallel-running strands are further interconnected by actetate bridging ligands forming Cd2O2 four-membered connections. The double-stranded coordination polymer is taken into the second dimension by intermolecular hydrogen bonding between the oxygen atoms of the acetate bridge and a tetrameric water cluster. Interaction of L with Cd(NO3)2·4H2O leads to the formation of [Cd(NO3)2(L)(MeOH)]n (2). In the presence of pyridine (Py), this reaction affords [Cd(NO3)2(L)(Py)2]n (3). In contrast to 1, compounds 2 and 3 are single-strand one-dimensional (1-D) coordination polymers. In 1−3, the cadmium atoms are seven-coordinate in a pentagonal−bipyramidal geometry. The reaction of L with ZnCl2, MnCl2, or CoCl2 leads to the formation of [{Zn(Cl)2(L)}(MeOH)]n (4), [Mn(Cl)2(L)2]n (5), and [Co(Cl)2(L)2]n (6). Structure 4 is a simple 1-D coordination polymer containing tetrahedral zinc atoms, while 5 and 6 are macrocycle-linked coordination polymers. In the latter, successive metal atoms are linked by a pair of carbophosphazene ligands to generate 24-membered macrocyclic rings which are interconnected to each other at the metal center to afford the coordination polymer chain.

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2011

Journal Article

V. Chandrasekhar, Pandey, M. D., Das, B., Mahanti, B., Dr. Gopal K., and Azhakar, R., “Synthesis, structure and photo-physical properties of phosphorus-supported fluorescent probes”, Tetrahedron, vol. 67, pp. 6917 - 6926, 2011.[Abstract]


Various phosphorus-supported fluorescent probes have been synthesized by the condensation reaction of multi-functional phosphorus hydrazides with various fluorophore-containing carboxaldehydes. Compounds, thus prepared, in this study are (PhO)2P(O)[N(Me)–NCH–R] (1a, 1b), Ph2P(O)[N(Me)–NCH–R] (2b, 2c, 2d), PhP(O)[N(Me)–NCH–R]2 (3b, 3c), P(S)[N(Me)–NCH–R]3 (4b, 4c), P(O)[N(Me)–NCH–R]3 (5a, 5b, 5c), N3P3(O2C12H8)2[N(Me)–NCH–R]2 (6a, 6b, 6c), N3P3(O2C12H8)[N(Me)–NCH–R]4 (7a, 7b, 7c, 7d) and N3P3[N(Me)–NCH–R]6 (8b, 8c), where R=1-pyrenyl (a), 9-anthracenyl (b), 9-phenanthryl (c) and 7-(N,N′-diethylamino)-3-coumarinyl (d). All of these compounds have been characterized by various analytical techniques including 31P{1H} \{NMR\} spectroscopy. Compounds 1b, 2b, 3b, 4b, 5b, 5c and 6d have also been characterized by single crystal X-ray analysis. All of these phosphorus-supported compounds exhibit excellent fluorescence properties in aqueous solution at near physiological conditions.

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2011

Journal Article

Dr. Gopal K., Tuna, F., and Winpenny, R. E. P., “Octa-and hexametallic iron (III)–potassium phosphonate cages”, Dalton Transactions, vol. 40, pp. 12044–12047, 2011.[Abstract]


Two new iron(III)-potassium phosphonate cage complexes with {K2Fe6} and {K2Fe4} cores are reported. Magnetic studies reveal antiferromagnetic interactions between the Fe(III) centres occur in these cages.

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2010

Journal Article

V. Baskar, Dr. Gopal K., Helliwell, M., Tuna, F., Wernsdorfer, W., and Winpenny, R. E. P., “3d–4f Clusters with Large Spin Ground States and SMM Behaviour”, Dalton Transactions, vol. 39, pp. 4747–4750, 2010.

2009

Journal Article

V. Chandrasekhar, Dr. Gopal K., Singh, P., Narayanan, R. Suriya, and Duthie, A., “Self-Assembly of Organostannoxanes: Formation of Gels in Aromatic Solvents”, Organometallics, vol. 28, pp. 4593-4601, 2009.[Abstract]


Organostannoxane drums [n-BuSn(O)O2C-C6H4-4-OR]6 [R = −CH3 (1); −C9H19 (2); −C11H23 (3)] and [n-BuSn(O)O2C-C6H3-3,5-(OR)2]6 [R = −CH3 (4); −C9H19 (5)] were synthesized by the reaction of n-BuSn(O)(OH) with the corresponding carboxylic acid in a 1:1 stoichiometry. Analogous reactions involving [n-Bu2SnO]n in a 1:1 stoichiometry afforded the diorganostannoxane ladders {[n-Bu2SnO2C-C6H4-4-OR]2O}2 [R = −CH3 (6); −C9H19 (7); −C11H23 (8)] and {[n-Bu2SnO2C-C6H3-3,5-(OR)2]2O}2 [R = −CH3 (9) and −C9H19 (10)]. Compounds 1−10 could also be prepared by a solventless methodology, which involved grinding the reactants together in a mortar and pestle at room temperature. Compounds 1−10 exhibit gelation behavior in aromatic solvents. In contrast, in aliphatic solvents gelation behavior was not observed. Among the organostannoxanes reported here, 2, 3, 5, and 8 were found to be extremely efficient gelators based on their critical gelation concentration values. The microstructure of the organometallic gels, investigated by optical and scanning electron microscopy, reveals the presence of cross-linked network structures. The gels formed from 2 and 3 can be converted into xerogels by removal of solvent. The latter can be reconverted into the original gels by treatment with aromatic solvents.

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2007

Journal Article

V. Chandrasekhar, Dr. Gopal K., and Thilagar, P., “Nanodimensional Organostannoxane Molecular Assemblies”, Accounts of Chemical Research, vol. 40, pp. 420-434, 2007.[Abstract]


Organooxotin cages, clusters, and coordination polymers containing [Sn2(μ-O)], [Sn2(μ-OH)], [Sn2(μ-O)2], [Sn2(μ-OH)2], and [Sn3(μ3-O)(μ-OR)3] building blocks have been assembled by the reactions of organotin precursors with phosphonic, phosphinic, carboxylic, or sulfonic acids. Various synthetic methodologies including Sn–C bond cleavage reactions and solventless procedures have been utilized to generate several nanodimensional organostannoxane assemblies. The synthesis, structure, and structural interrelationship of these diverse organostannoxane compounds are discussed. The synthetic knowledge gained to prepare specific organostannoxane structural forms in high yields has been utilized for the construction of dendrimer-like molecules. These contain a central stannoxane core and a functional periphery. The functional periphery can be readily modulated to assemble photoactive, electroactive, or multisite coordinating molecules. The synthesis, structure, and potential uses of these compounds are discussed.

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2007

Journal Article

V. Chandrasekhar, Singh, P., and Dr. Gopal K., “Direct Hydrolysis of Hydrated Organotin Cations:  Synthesis and Structural Characterization of [n-Bu2Sn(OH2)(Phen)(O3SC6H3-2,5-Me2)]+[2,5-Me2C6H3SO3]- (Phen = 1,10-phenanthroline) and [n-Bu2Sn(μ-OH)(O3SC6H3-2,5-Me2)]2n”, Organometallics, vol. 26, pp. 2833-2839, 2007.[Abstract]


The reaction of {[n-Bu2Sn(OH2)4]2+[2,5-Me2C6H3SO3-]2} (2) with 1,10-phenanthroline affords {[n-Bu2Sn(OH2)(Phen)(O3SC6H3-2,5-Me2)]+[2,5-Me2C6H3SO3]-} (3) by the displacement of two water molecules by the chelating phenanthroline ligand and one water molecule by a sulfonate ligand. In contrast, 2 undergoes hydrolysis on treatment with pyridine, resulting in the formation of {[n-Bu2Sn(μ-OH)(O3SC6H3-2,5-Me2)]2}n (4). Formation of 4 also occurs in the reaction of 3 with pyridine as well as in a 1:1 reaction of [n-Bu2SnO]n with 2,5-Me2C6H3SO3H·2H2O. The molecular structure of 3 contains a six-coordinate tin with a coordination environment comprising the chelating phenanthroline ligands, two butyl substituents, one water molecule, and one sulfonate ligand. Extensive hydrogen-bonding interactions (O−H- - -O, C−H- - -O, and O- - -π) in the crystal structure result in the formation of a three-dimensional supramolecular architecture for 3. The crystal structure of 4 reveals that it is a two-dimensional coordination polymer. The basic repeat unit of the coordination polymer contains a [Sn(μ-OH)]2 distannoxane ring. Anisobidentate coordination action of the sulfonate ligand results in the generation of 20-membered macrocycles, which are linked to each other to form the two-dimensional coordination polymer network.

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2007

Journal Article

V. Chandrasekhar, Singh, P., and Dr. Gopal K., “Organotin compounds containing four-membered distannoxane [Sn(µ-OH)]2 units”, Applied Organometallic Chemistry, vol. 21, pp. 483–503, 2007.[Abstract]


Compounds containing the distannoxane core [Sn(µ-OH)]2 are reviewed. Synthesis and structural aspects of these compounds are summarized in this article.

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2006

Journal Article

V. Chandrasekhar, Dr. Gopal K., Nagendran, S., Steiner, A., and Zacchini, S., “Influence of Aromatic Substituents on the Supramolecular Architectures of Monoorganooxotin Drums”, Crystal Growth & Design, vol. 6, pp. 267-273, 2006.[Abstract]


The reaction of n-BuSn(O)(OH) with various substituted benzoic acids affords hexameric organostannoxane drums, [n-BuSn(O)OC(O)R]6, where R = 2,6-(CH3)2−C6H3 (1), 4-CH3−C6H4 (2), 4-NH2−C6H4 (3) and 2-NH2−C6H4 (4). The central stannoxane motif (Sn6O6) is similar in all these compounds and is surrounded by six substituted benzoate groups. All the drums show an extensive supramolecular organization in the solid state. Accordingly, drum 1 forms a one-dimensional supramolecular assembly mediated by noncovalent interactions such as C−H···O and π···π interactions. Similarly, drums 2−4 form interesting three-dimensional supramolecular assemblies mediated by C−H···O, N−H···N, C−H···π, and π···π interactions in the solid state. The role of the peripheral aromatic substituents in determining the final course of the supramolecular assembly is discussed.

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2006

Journal Article

V. Chandrasekhar, Boomishankar, R., Dr. Gopal K., Sasikumar, P., Singh, P., Steiner, A., and Zacchini, S., “Synthesis, Structure and Reactivity of Hydrated and Dehydrated Organotin Cations”, European Journal of Inorganic Chemistry, vol. 2006, pp. 4129–4136, 2006.[Abstract]


Monomeric organotin dications {[nBu2Sn(H2O)4]2+·2C6H5SO3–} and {[nBu2Sn(H2O)4]2+·1,5-C10H6(SO3–)2} have been synthesized by the reaction of [nBu2SnO]n and the corresponding arylsulfonic acid. Dodecanuclear organooxotin macrocations {[(nBuSn)12(μ3-O)14(μ2-OH)6]2+·2RSO3–} (R = C6H5; 2,5-Me2C6H3) have been synthesized by the reaction of nBuSn(O)(OH) and the corresponding arylsulfonic acid. The X-ray crystal structure of one of the dodecanuclear cages is reported. These organotin cations have been shown to be effective catalysts in acetylation and transacetylation reactions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

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2006

Journal Article

V. Chandrasekhar, Dr. Gopal K., Nagarajan, L., Sasikumar, P., and Thilagar, P., “Stannoxanes and phosphonates: New approaches in organometallic and transition metal assemblies”, Journal of Chemical Sciences, vol. 118, pp. 455–462, 2006.[Abstract]


Phosphonate ligands, [RPO3]2-, are extremely versatile in the assembly of multi-tin and multi-copper architectures. We have used organostannoxane cores for supporting multi-ferrocene and multi-porphyrin peripheries. The copper-metalated multi-porphyrin compound is an excellent reagent for facile cleavage of DNA, even in the absence of a co-oxidant. Reaction oft-BuPO3H2 with Cu(C104)2. 6H2O in the presence of 2-pyridylpyrazole (2-Pypz) leads to the synthesis of a decanuclear copper (II) assembly.

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2005

Journal Article

V. Chandrasekhar, Dr. Gopal K., Nagendran, S., Singh, P., Steiner, A., Zacchini, S., and Bickley, J. F., “Organostannoxane-Supported Multiferrocenyl Assemblies: Synthesis, Novel Supramolecular Structures, and Electrochemistry”, Chemistry – A European Journal, vol. 11, pp. 5437–5448, 2005.[Abstract]


Organostannoxane-based multiredox assemblies containing ferrocenyl peripheries have been readily synthesized by a simple one-pot synthesis, either by a solution method or by room-temperature solid-state synthesis, in nearly quantitative yields. The number of ferrocenyl units in the multiredox assembly is readily varied by stoichiometric control as well as by the choice of the organotin precursors. Thus, the reaction of the diorganotin oxides, R2SnO (R=Ph, nBu and tBu) with ferrocene carboxylic acid affords tetra-, di-, and mononuclear derivatives [{Ph2Sn[OC(O)Fc]2}2] (1), [{[nBu2SnOC(O)Fc]2O}2] (2), [nBu2Sn{OC(O)Fc}2] (3), [{tBu2Sn(OH)OC(O)Fc}2] (4), and [tBu2Sn{OC(O)Fc}2] (5) (Fc=η5C5H4-Fe-η5C5H5). The reaction of triorganotin oxides, R3SnOSnR3 (R=nBu and Ph) with ferrocene carboxylic acid leads to the formation of the mono-nuclear derivatives [Ph3SnOC(O)Fc] (6) and [{nBu3SnOC(O)Fc}n] (7). Molecular structures of the compounds 1–4 and 6 have been determined by single-crystal X-ray analysis. The molecular structure of compound 1 is new among organotin carboxylates. In this compound, ferrocenyl carboxylates are involved in both chelating and bridging coordination modes to the tin atoms to form an eight-membered cyclic structure. In all of these compounds, the acidic protons of the cyclopentadienyl groups are hydrogen bonded to the carboxylate oxygens (C[BOND]H⋅⋅⋅O) to form rich supramolecular assemblies. In addition to this, π–π, T-shaped, L-shaped, and side-to-face stacking interactions involving ferrocenyl groups also occur. Compound 6 shows an interesting and novel intermolecular CO2–π stacking interaction. Electrochemical analysis of the compounds 1–4, 6, and 7 shows a single, quasi-reversible oxidation peak corresponding to the simultaneous oxidation of four, two, and one ferrocenyl substituents, respectively. Compound 5 shows two quasi-reversible oxidation peaks. This is attributed to the positional difference among the ferrocenyl substituents on the tin atom. Additionally, while compounds 2 and 4 are electrochemically quite robust and do not decompose even after ten continuous CV cycles, compounds 1, and 3, 5–7 start to show decomposition after five cycles.

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2005

Journal Article

V. Chandrasekhar, Baskar, V., Dr. Gopal K., and Vittal, J. J., “Organooxotin Cages, {[(n-BuSn)3(μ3-O)(OC6H4-4-X)3]2[HPO3]4”, Organometallics, vol. 24, pp. 4926-4932, 2005.[Abstract]


The reaction of n-BuSn(O)(OH) with H3PO3 and HOC6H4-4-X (X = H, Cl, Br, and I) afforded the hexanuclear organooxotin cages {[(n-BuSn)3(μ3-O)(OC6H4-4-X)3]2[HPO3]4}, where X = H (1), Cl (2), Br (3), and I (4), in moderate yields. These cages possess double O-capped structures. The oxotin cages 1−4 contain two tritin motifs that are joined by four tripodal [HPO3]2- ligands. The three tin atoms in each tritin subunit are held together by a μ3-capping oxygen atom. In addition three phenolate oxygen atoms act as μ2-bridging ligands between two tin atoms. The molecular structures of 1−4 are intimately related to other organooxotin cages such as the O-capped cluster, the drum, and the football cage. The crystal structures of 2−4 reveal intermolecular halogen-bonding-mediated [X- - -O (X = Cl, Br), I- - -I, and I- - -π] supramolecular assemblies.

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2005

Journal Article

V. Chandrasekhar, Nagarajan, L., Dr. Gopal K., Baskar, V., and Kögerler, P., “A New Structural Form for a Decanuclear Copper (II) Assembly”, Dalton Transactions, pp. 3143–3145, 2005.[Abstract]


The synthesis and structure of a novel decanuclear copper(II) cage is reported. The assembly of the cage is facilitated by the cumulative coordinative interaction of tert-butyl phosphonate, 2-pyridylpyrazole and hydroxide ligands with copper(II) ions. Magnetic studies of this decanuclear copper(II) cage indicate complex antiferromagnetic behaviour.

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2005

Journal Article

V. Chandrasekhar, Boomishankar, R., Azhakar, R., Dr. Gopal K., Steiner, A., and Zacchini, S., “N-Bonded Monosilanols: Synthesis and Characterization of ArN(SiMe3)SiMe2Cl and ArN(SiMe3)SiMe2OH (Ar = C6H5, 2,6-Me2C6H3,2,6-iPr2C6H3)”, European Journal of Inorganic Chemistry, vol. 2005, pp. 1880–1885, 2005.[Abstract]


{By the use of aniline and the sterically hindered aromatic primary amines, 2,6-Me2C6H3NH2 and 2,6-iPr2C6H3NH2, N-bonded monochlorosilanes, ArN(SiMe3)SiMe2Cl [Ar = C6H5 (1a)

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2005

Journal Article

V. Chandrasekhar, Dr. Gopal K., Sasikumar, P., and Thirumoorthi, R., “Organooxotin assemblies from SnC bond cleavage reactions”, Coordination Chemistry Reviews, vol. 249, pp. 1745 - 1765, 2005.[Abstract]


Organooxotin compounds can be assembled by using various synthetic methodologies. Although in most instances, organotin oxides and hydroxides are the preferred starting materials for preparing organooxotin compounds, SnC bond cleavage reactions involving organotin compounds also offer a rational route. This review deals with the recent progress in this area and examines various reactions, where SnC cleavage occurs. A wide range of products are accessible from this approach and these are presented in this article.

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2005

Journal Article

V. Chandrasekhar and Dr. Gopal K., “Monoorganotin(IV) phosphonates”, Applied Organometallic Chemistry, vol. 19, pp. 429–436, 2005.[Abstract]


Recent progress in the assembly of monoorganotin(IV) phosphonates is reviewed. The molecular structures of these compounds and their dependence on the nature of the organotin precursor and that of the phosphonic acid are discussed.

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2003

Journal Article

V. Chandrasekhar, Nagendran, S., Dr. Gopal K., Steiner, A., and Zacchini, S., “First example of a Sn–C bond cleaved product in the reaction of Ph 3 SnOSnPh 3 with carboxylic acids. 3D-Supramolecular network formation in the X-ray crystal structure of [Ph 2 Sn (OH) OC (O)(R f)] 2, R f= 2, 4, 6-(CF 3) 3 C 6 H 2”, Chemical Communications, pp. 862–863, 2003.[Abstract]


A 1∶2 reaction of Ph3SnOSnPh31 with RfCOOH 2 leads to the formation of [Ph2Sn(OH)OC(O)(Rf)]23, by means of a facile Sn–C bond cleavage process.

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2003

Journal Article

V. Chandrasekhar, Baskar, V., Boomishankar, R., Dr. Gopal K., Zacchini, S., Bickley, J. F., and Steiner, A., “Solventless Reactions for the Synthesis of Organotin Clusters and Cages”, Organometallics, vol. 22, pp. 3710-3716, 2003.[Abstract]


Organotin clusters and cages have been synthesized in quantitative yields by using a benign solventless synthetic methodology. Using this method a variety of structural forms, which include the drum, O-capped cluster, tetranuclear oxo cage, discrete, and polymeric compounds, have been synthesized. All these compounds (1−11) have been characterized by spectroscopic and analytical techniques. The new compounds, which include the hexameric drum [n-BuSn(O)OCOAd]6 (Ad = adamantyl) 9, a triorganotin-based discrete structure Ph3SnO2C-C6H2-2,4,6-Me3 (10), and a polymer Ph3SnOSO2-C6H3-2,5-Me2 (11), have been characterized by single-crystal X-ray crystallography.

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Publication Type: Book Chapter

Year of Publication Publication Type Title

2011

Book Chapter

Dr. Gopal K., Ali, S., and Winpenny, R. E. P., “Structural Studies of Paramagnetic Molecular Phosphonates”, in Metal Phosphonate Chemistry: From Synthesis to Applications (Editors: A. Clearfield and K. Demadis) , Royal Society of Chemistry, 2011.[Abstract]


Routes to paramagnetic molecular phosphonates and physical studies of these species will be discussed in this chapter. The routes include:use of co-ligands to solubilize the molecular species and prevent formation of extended latticesdisplacement reactions, where phosphonates are reacted with pre-formed metal carboxylate cagesuse of very bulky phosphonates to prevent oligomerizationpartial condensation of phosphonates with antimonates to restrict the number of oxygen donors available.

These routes have been applied to the 3d-metals from vanadium to copper, and examples with each metal will be discussed. An outline of the magnetic studies thus far reported will also be included.

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2008

Book Chapter

V. Chandrasekhar, Singh, P., and Dr. Gopal K., “Organotin Carboxylate and Sulfonate Clusters”, in Tin Chemistry: Fundamentals, Frontiers, and Applications, John Wiley & Sons, 2008.

  
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