EXPERIMENTAL AND THEORETICAL DENSITY STUDIES ON A NITRIDO-CHROMIUM(V) COMPLEX [CR-V(BPB)N]

This work gives the first example of a combined experimental and theoretical electron density study of a M-N-nitrido triple bond. The electron density distribution of a chromium(V)-nitrido complex, Cr-V(bpb)N (bpb(2-) = 1,2-bis(2-pyridinecarboxamido)benzene), was investigated both by single-crystal X-ray diffraction measurement at 120 K and by molecular orbital calculations. The compound belongs to the space P2(1), Z = 2, M(r)= 382.32, a = 5.977(1) Angstrom, b = 13.208(2) Angstrom, c = 9.776(1) Angstrom, beta = 90.27(1)degrees, V = 771.7(2) Angstrom(3), Mo K alpha radiation (lambda = 0.7107 Angstrom, mu = 0.75 mm(-1)), R(f) = 4.1%, and R(w) = 2.5% for 5975 observed reflections. Cr is five-coordinated in a square pyramidal fashion. There are three different Cr-N bonds in this compound, namely, Cr-N-nitrido, Cr-N-amido, and Cr-N-pyridine bonds. Deformation density maps were derived from the multipole model and from the theoretically calculated ones based on ab initio and DFT (density functional theory) calculations. The accumulation of deformation density along the C-H, C-C, C-N, and C-O bonds in the bpb ligand is clearly demonstrated for their covalent character. The agreement between the density maps obtained from the multipole model and from molecular orbital calculations is excellent in the ligand part. Some discrepancies are found near the Cr nucleus. Net atomic charges from multipole refinement are in reasonable agreement with those derived from ab initio calculations and the DFT method. Analysis of natural. bonding orbitals (NBOs) reveals that the Cr-N-nitrido has a triple-bond character (sigma(2) pi(4)) and the four N of bpb behave as sigma-donors to Cr with Cr-N-amido a polarized covalent bond and Cr-N-pyridine an essentially dative bond. d-orbital populations of Cr are derived by both experiment and theory; they are in good agreement with each other. An unpaired electron is found on the nonbonding d-orbital of the Cr atom.