DFT calculation and X-ray structure of nitrosyl pentaammine chromium complex

The optimized structures of nitrosyl pentaammine chromium complex [Cr(NO)(NH 3 ) 5 ] 2+ ( A ) at three different spin multiplicities, doublet ( A2 ), quartet ( A4 ), and sextet ( A6 ), were obtained by ab initio calculation at B3LYP/6-31G ∗ (6-31+G ∗ for NO) level of theory. The complex A was most stable at the lowest spin multiplicity (doublet), which is in harmony with the previous magnetic measurement ( μ eff =1.8 BM) of the perchlorate of A , [Cr(NO)(NH 3 ) 5 ](ClO 4 ) 2 ( A ′ ) . The X-ray structure of A ′ was determined: Cr–N(NO), 1.677(6) A; N–O, 1.180(7) A; Cr–N(NH 3 , trans ), 2.140(5) A; Cr–N(NH 3 , cis ), 2.080(6)–2.096(6) A; Cr–N–O, 179.9(6)°. The optimized structure ( A2 ) is in good agreement with the experimental one. The present result shows that the covalent type π bondings between Cr and N(NO), which is ascribed to the overlapping between two π ∗ orbitals of NO and two π orbitals of Cr, cause the extra stabilization of A2 .