Spectroscopic studies of a square-pyramidal nitridochromium(V) complex

Abstract

The ESR and UV/VIS spectra have been studied for solutions of [N,N′-bis(pyridine-2-carbonyl)-o-phenylenediamido]nitridochromium(V) having a square-pyramidal (CrN₅) chromophore. The g and ⁵³Cr hyperfine coupling tensors (A) are axially symmetric. An analysis of the A tensor indicated a 3d_xy ground-state Kramers doublet. Fairly high d_π–p_π interaction in the CrN formally triple bond was also revealed. The striking stability of this complex can be attributed to the remarkable d_π–p_π covalency of the CrN bond. None of the d–d* transitions has been observed in the region of λ 600 nm at room temperature. Bands at 25 000 and 29 000 cm^–1 have been tentatively assigned to charge-transfer transitions. The considerable difference between the A_⊥(⁵³Cr), a(⁵³Cr), g_⊥ and g_iso values of nitrido-and those of oxo-chromium(V) complexes have been explained in terms of the different extents of covalency in the CrN and CrO multiple bonds.