PERTURBATION-THEORY AND THE EFFECTS OF SUBSTITUTION IN SQUARE AND BIPYRAMIDAL SIGMA-BONDED COMPOUNDS

The effects of substitution of L by L in square EL4 and bipyramidal [trigonal (TB) EL5, tetragonal(octahedral)EL6> and pentagonal (PB) EL7] σ-bonded complexes, for E a transition metal M or main group element A, have been considered in the framework of the perturbation theory of canonical MOs. The difference in ligand σ orbital energies, α=α(L‘)-α(L), where σ > 0 (<0) correspond to a better donor (acceptor) substituent L was taken as a perturbation and all changes in overlap populations of different E-L bonds. σN(E-L)σα were obtained in terms of the nS, np, and (n-1)dcontributions. It was found that in all transition metal complexes MLm the is and d contributions to σN(MLtrans)/σα are always negative and bigger in absolute value than the p one. which is always positive. The is and d contributions to σN(M-Lcis)/σα are always of opposite sign, typically the is ohc positive and the d one negative, so that SσN(M-Lcis) will be smaller in absolute value than σN(M-Ltr) and may be of any sign. The effccts of substitution in main group element complexes ALm strongly depend on the oxidation state of the central atom. The role of π-bonding effccts was also briefly discussed. The results obtained agree with experiment and permit the fundamental regularities of substitution, particularly the trans and cis influence, in ELm-kLk complexes, to be explained and predicted. © 1979, American Chemical Society. All rights reserved.