Relation Between the Structure and Spectra of Pseudotetrahedral CuN₄ Complexes and the Crystal Structure of [CuL₂](ClO₄)₂, L = 2-pyridyl-2-pyrimidylamine

The crystal structure of the title complex has been determined. The copper environment is pseudotetrahedral, with a dihedral angle, φ, of 53.8° between the two CuN2 ligand planes. The two ligands are identical as required by crystallographic symmetry. The two perchlorate groups are ionic, 3.369 (1) Å away from the copper atom on opposite sides. This result suggests the hypothesis of a correlation between the spectra and structures of pseudotetrahedral CuN4 species. The electronic spectrum of [Cu(MPA)2], which has φ = 57.4°, is very similar to that of [Cu(PTA)2], suggesting similar values of φ for the two complexes and contradicting an earlier postulate of a less tetrahedral structure for [Cu(PTA)2] (HMPA = 3,3′-dimethyl-2,2′-dipyridylamine, HPTA = 2-pyridyl-2-thiazolylamine). Crystal data for [Cu(HPPA)2](ClO4)2: space group C2/c, Z = 4, a = 9.356 (8) Å, b = 12.752 (2) Å, c = 19.353 (4) Å, β = 101.56 (3)°, V = 2262 Å3, R = 4.6% for 1893 reflections. © 1980 American Chemical Society