Geometric distortions of octahedral cations and tetrahedral anions in disordered [Cu(bpy)_3]CrO_4·7.5H_2O crystal - A comparative study

摘要

A novel copper(II) chromate complex of the formula [Cu(bpy) _3][CrO_4]·7.5H_2O (1) (bpy = 2,2′-bipyridine) was prepared in the crystalline form and characterized by X-ray diffraction and spectroscopic methods (EPR, FIR-IR, NIR-Vis-UV). Two non-equivalent [Cu(bpy)_3]~(2+) groups in the form of tetragonally elongated octahedron are built into the hydrogen-bonded network. The tetragonality parameter T is 0.9830 and 0.9876 for Cu(1) and Cu(2) centers, respectively, points to the significant Jahn-Teller (JT) distortion in the tris-bipyridine copper(II) cations. The EPR parameters g_1, g _2 and g_3 are equal to 2.168, 2.159 and 2.072, respectively, correspond to the Cu-N bond directions oscillating between long and short distances. The chromate moiety is a non-coordinated to the metal center and forms a very distorted tetrahedron with three bond lengths in the range 1.617(2)-1.629(2). The O(3A) and O(3B) atoms execute reorientational motion between two equilibrium arrangements with equal probability. The related geometric distortion, Δ_r, is 0.097. The Gaussian analysis of single crystal electronic spectra was based on the four d-d bands assigned for Cu(II) center to the ~2A_(1g(dx2-y2)) → ~2A_(2g(dz2)), ~2B_(1g(dxy)), ~2B_(2g(dxz)) and ~2B_(3g(dyz)) transitions in D_(2h) symmetry.