Nephelauxetic series of in-plane ligands for square-pyramidal nitridochromium(V) complexes as studied by means of ESR spectroscopy

The crystal structure of the nitridochromium(V) complex [CrN(salophen)] · MeCN [H₂salophen=N,N′-bis(salicylidene)-o-phenylene-diamine] has been determined. The coordination geometry of this complex, similar to those of all the nitridochromium(V) complexes investigated so far, is square pyramidal with the nitride ion occupying the apex. The ESR parameters of the nitridochromium(V) complexes isolated so far were compared with one another to show an enormous expansion of the 3d electron cloud due to the strong Cr=N triple bonding. Moderate covalency in the in-plane bonds was also concluded. The nephelauxetic series of three types of the basal ligands is deduced to be salen≈salophen>bpb≈mebpb≈dmebpb>oep≈ttp (in nephlauxetic ratio) for the high-oxidation nitridochromium(V), H₂salen=N,N′-bis(salicylidene)ethane-1,2-diamine, H₂bpb=1,2-bis(pyridine-2-carboxamido)benzene, H₂mebpb=1,2-bis(pyridine-2-carboxamido)-4-methylbenzene, H₂dmbpb=1,2-bis(pyridine-2-carboxamido)-4,5-dimethylbenzene, H₂oep=2,3,7,8,12,13,17,18-octa-ethylporphyrin and H₂ttp=5,10,15,20-tetra-p-tolylporphyrin.