MOLECULAR-STRUCTURE OF ELECTRON DONOR-ACCEPTOR COMPLEXES OF METALLOTETRAPHENYLPORPHYRINS WITH TRINITROBENZENE

The metallotetraphenylporphyrins, MTPPs, where M = Co(II), Cu(II) and Ag(II) form one to one molecular complexes in solution with 1,3,5-trin itrobenzene (TNB). The crystal structure of CoTPP.TNB.2CH3OH revealed that the mean separation between the porphyrin and TNB planes is 3.27 angstrom and the centre of the aryl ring of TNB is displaced by 0.90 a ngstrom from the centre of the porphyrin plane. Extended Huckel molecu lar orbital calculations suggest that the acceptor orbitals are predom inantly nitro-group based rather than an aryl pi framework. The contri bution of the metal orbitals in the donation is also seen as predicted by the structural data. Electrochemical redox measurements in solutio n provide evidence for charge-transfer stabilisation in these complexe s.