Synthesis, Structure, and Magnetic and Electrochemical Properties of Quasi-Linear and Linear Iron(I), Cobalt(I), and Nickel(I) Amido Complexes

Three potassium crown ether salts, [K­(Et2O)2(18-crown-6)]­[Fe­{N­(SiMe3)­Dipp}2] (1a; Dipp = C6H3-2,6-Pri2), [K­(18-crown-6)]­[Fe­{N­(SiMe3)­Dipp}2]·0.5PhMe (1b), and [K­(18-crown-6)]­[M­{N­(SiMe3)­Dipp}2] (M = Co, 2; M = Ni, 3), of the two-coordinate linear or near-linear bis-amido monoanions [M­{N­(SiMe3)­Dipp}2]− (M = Fe, Co, Ni) were synthesized by one-electron reduction of the neutral precursors M­{N­(SiMe3)­Dipp}2 with KC8 in the presence of 18-crown-6. They were characterized by X-ray crystallography, UV–vis spectroscopy, cyclic voltammetry, and magnetic measurements. The anions feature lengthened M–N bonds in comparison with their neutral precursors, with slightly bent coordination (N–Fe–N = ca. 172°) for the iron­(I) complex, but linear coordination for the cobalt­(I) and nickel­(I) complexes. Fits of the temperature dependence of χMT of 1 and 2 reveal that the iron­(I) and cobalt­(I) complexes have large negative D zero-field splittings and a substantial orbital contribution to their magnetic moments with L = 2, whereas the nickel­(I) complex has at most a small orbital contribution to its magnetic moment. The magnetic results have been used to propose an ordering of the 3d orbitals in each of the complexes.