Crystal structures and electronic properties of three fluxional [Cu(di-2-pyridylamine)2(OXO)]Y complexes

The crystal structures of three bis( dpyam) copper( II) complexes, [ Cu( dpyam) 2( ONO)] (SO4)(0.5)(H2O) (I), [Cu( dpyam)(2)(O2CCH3)](ClO4) (II) and [Cu(dpyam)(2)(O2CCH2CH3)](ClO4) ( III) ( dpyam di-2- pyridylamine) have been determined at room temperature by single-crystal X- ray methods. The complexes involve a CuN4O2 chromophore with a symmetric cis- distorted octahedral stereochemistry for I, and an asymmetric cis- distorted octahedral stereochemistry for II and III. In I the copper atom and the oxygen donor atoms of the symmetrically bonded nitrito group lie on a crystallographic C-2 axis. This is the first reported example in the literature of such a complex with this type of stereochemistry, involving the [ Cu( dpyam)(2)( OXO)][Y] series as a whole, where (OXO)(-) involves an oxoanion. In contrast, complexes II and III involve a distortion of the CuN4O2 chromophore towards a square pyramidal ( 4 + 1 + 1) stereochemistry. Here, the stereochemistries of I, II and III are compared with other closely related complexes. The highly asymmetric geometry of the CuN4O2 chromophores of II and III suggests that both complexes appear to be static in nature. Electronic spectra of the three complexes involve two bands of similar intensity corresponding to cis- distorted octahedral copper( II) stereochemistry.