SPECTROSCOPIC STUDIES OF A SQUARE-PYRAMIDAL NITRIDOCHROMIUM(V) COMPLEX

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 Cr-53 hyperfine coupling tensors (A) are axially symmetric. An analysis of the A tensor indicated a 3d(xy) ground-state Kramers doublet. Fairly high d(pi)-p(pi) interaction in the Cr=N formally triple bond was also revealed. The striking stability of this complex can be attributed to the remarkable d(pi)-p(pi) covalency of the Cr=N bond. None of the d-d* transitions has been observed in the region of lambda greater than or equal to 600 nm at room temperature. Bands at 25000 and 29000 cm(-1) have been tentatively assigned to charge-transfer transitions. The considerable difference between the A(perpendicular to)(Cr-53), a(Cr-53), g(perpendicular to) 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 Cr=N and Cr=O multiple bonds.