Crystal structures and spectroscopic properties of copper(Ⅱ) pseudohalide complexes with two sparteine epimers, having a CuN₄ chromophore

Tetrahedrally distorted copper(Ⅱ) sparteine pseudohalide complexes having a CuN4 chromophore were prepared and characterized by various spectroscopic techniques and X-ray crystallography. Among them, the crystal structures of copper(Ⅱ) isothiocyanate complexes with two sparteine epimers, (-)-l-sparteine (Sp) and (-)-α-isosparteine (α-Sp), were determined. The NSp–Cu–NSp plane in copper(Ⅱ) (-)-l-sparteine isothiocyanate [Cu(Sp)(NCS)₂] and copper(Ⅱ) (-)-α-isosparteine isothiocyanate [Cu(a-Sp)(NCS)₂] is twisted by 58.2(6)° and 52.2(9)°, respectively, from the NNCS–Cu–NNCS plane. Based on the values of the dihedral angles and tilted distances of these two complexes, the geometry around Cu(Ⅱ) in Cu(α-Sp)(NCS)2 is more distorted from the perfect tetrahedron than that in Cu(Sp)(NCS)₂. For copper(Ⅱ) sparteine pseudohalide (NCS⁻ and N₃⁻) complexes having a CuN₄ chromophore, the EPR and the optical spectral data were collected. The results of X-ray crystallography and ESR spectroscopy are in a good agreement with the assumption that the degree of distortion from planarity to tetrahedron will reduce the AⅡ value of four-coordinate copper(Ⅱ) sparteine pseudohalide complexes.