Crystal structure and electronic spectrum of the distorted tetrahedral CuCl42- ion in bis(2-aminopyridinium) tetrachlorocuprate(II) and comparison with the tetragonally elongated octahedral complex bis(2-aminopyrimidinium)tetrachlorocopper(II)

The crystal structure of bis(2-aminopyridinum) tetrachlorocuprate(II) has been determined by single-crystal X-ray diffraction. The triclinic unit cell, space group P (1) over bar, contains a single formula unit in the asymmetric unit. The CuCl42- ions occur as isolated groups having a highly flattened tetrahedral geometry. The chloride ions are hydrogen-bonded to both nitrogen atoms of the cation, and the influence of this upon the geometry of the copper(II) complex is discussed. The low-temperature single-crystal electronic spectrum of the compound is reported, and the intensities and energies of the d-d transitions are related to the degree of distortion of the CuCl42- ion. The electronic spectrum of a crystal of bis(2-aminopyrimidinium)tetrachlorocopper(II) which contains a tetragonally elongated octahedral complex in which the cation forms long axial bonds to the copper(II) ion, was also measured for comparison. Angular overlap metal-ligand bonding parameters are derived for the two compounds, and discussed in terms of the different geometries of the complexes.