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 hav ing a highly flattened tetrahedral geometry. The chloride ions are hyd rogen-bonded to both nitrogen atoms of the cation, and the influence o f this upon the geometry of the copper(II) complex is discussed. The l ow-temperature single-crystal electronic spectrum of the compound is r eported, and the intensities and energies of the d-d transitions are r elated 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 t he cation forms long axial bonds to the copper(II) ion, was also measu red for comparison. Angular overlap metal-ligand bonding parameters ar e derived for the two compounds, and discussed in terms of the differe nt geometries of the complexes.