Crystal Structure and Electronic Spectrum of the Distorted Tetrahedral CuCl₄^2- Ion in Bis(2-aminopyridinium) Tetrachlorocuprate(II) and Comparison With the Tetragonally Elongated Octahedral Complex Bis(2-aminopyrimidinium)tetrachlorocopper(II)

Abstract

The crystal structure of bis(2-aminopyridinum) tetrachlorocuprate (II) has been determined by single-crystal X-ray diffraction. The triclinic unit cell, space group Pī, 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.