Pulsed ENDOR and ESEEM study of [bis(maleonitriledithiolato)nickel]-:: An investigation into the ligand electronic structure

By a combination of Q-band pulsed ENDOR (electron nuclear double resonance) and X-band ESEEM (electron stimulated echo envelope modulation) techniques, we have determined the hyperfine tensors for ethylene (C1) and cyano (C2) carbons and N, of [Ni(mnt)(2)](-), along with the quadrupole tensor for nitrogen. These measurements give it electron spin densities of rho(C1) similar to 0.03 in the C1 2p(z) orbital, rho(C2) < 0.003, rho(N) similar to 0.01, such that in total, similar to 0.15 of the spin resides on the ligand atoms C and N, while the rest resides in the NiS4 core, giving rho(NiS4-) = 0.85. These results are compared with extended Huckel and density functional (BLYP) MO calculations, as well as with X alpha calculations reported earlier.