Publication Type:

Journal Article


Polyhedron, Volume 24, Number 5, p.679 - 684 (2005)





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 π-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.

Cite this Research Publication

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.