Abstract
Five new mononuclear iron(II) tris-ligand complexes, and four solvatomorphs, have been made from the azine-substituted 1,2,4-triazole ligands (L-azine): [Fe-II(L-pyridazine)(3)](BF4)(2) (1), [Fe-II(L-pyrazine)(3)](BF4)(2) (2), [Fe-II(L-pyridine)(3)](BF4)(2) (3), [Fe-II(L-2pyrimidine)(3)](BF4)(2) (4), and [Fe-II(L-4pyrimidine)(3)](BF4)(2) (5). Single-crystal XRD and solid-state magnetometry reveal that all of them are low-spin (LS) iron(II), except for solvatomorph 54H(2)O. Evans method NMR studies in CD2Cl2, (CD3)(2)CO and CD3CN show that all are LS in these solvents, except 5 in CD2Cl2 (consistent with L-4pyrimidine imposing the weakest field). Cyclic voltammetry in CH3CN vs. Ag/0.01m AgNO3 reveals an, at best quasi-reversible, Fe-III/II redox process, with E-pa increasing from 0.69 to 0.99V as the azine changes: pyridine< pyridazine<2-pyrimidine<4-pyrimidine< pyrazine. The observed E-pa values correlate linearly with the DFT calculated HOMO energies for the LS complexes.