Crystal structure and magnetic properties of a binuclear triketonate complex of five-co-ordinate copper(II) : bis[heptanetrionato(2–)]bis-pyridinedicopper(II)

Abstract

The crystal and molecular structures of the title compound have been determined by single-crystal X-ray diffraction photography. The structure was solved by Patterson and Fourier methods and refined anisotropically by the method of least squares to R 11·1 % for 1743 visually estimated observed reflections. The black crystals are triclinic, space group P, and the reduced unit cell, of dimensions a= 9·60, b= 9·94, c= 8·61 (±0·03)Å, α= 123·7, β= 91·6, γ= 108·2 (±0·3)°, contains one centrosymmetric binuclear molecule. The triketonate ligands are terdentate, with the central O atoms linking the Cu atoms to give a planar Cu₂O₂ ring with angles Cu–O–Cu 103 and O–Cu–O 77°. Each copper atom is bonded to four coplanar O atoms and a pyridine N atom in a square-pyramidal arrangement, with Cu–O 1·93 (mean) and Cu–N 2·32 Å, the two pyridine ligands being on opposite sides of the molecule. The effective magnetic moment per Cu falls from 0·75 at 335 to 0·0 B.M. at 87 K; the magnetic data are consistent with intramolecular exchange giving a singlet–triplet separation 2|J| 690 cm^–1, with g 2·09.