Density Functional Study of Spin State in CpM(NO)X2 (M = Mo, Cr; X = Cl, NH2, CH3):  Spectrochemical and Nephelauxetic Effects in Organometallic Compounds1

International audience; The relationship between spin state and metal−ligand bonding interactions in CpM(NO)X2 species was investigated using density functional computational techniques. The geometries of CpM(NO)Cl2 (M = Cr, Mo), CpCr(NO)(NH2)X, and CpCr(NO)(CH3)X (X = Cl, CH3) were optimized at the DFT-B3LYP level for both the diamagnetic (S = 0) and paramagnetic (S = 1) electronic configurations. While the geometric parameters of the singlet compounds matched well with structures determined experimentally, the Cr−NO bond lengths in the triplet species exceeded the experimentally observed range by a significant margin, thereby indicating a propensity for nitrosyl-ligand dissociation from t…