Crystal and molecular structure of deca-µ-acetato-dioxobis(pyridine)-heptazinc(II) and the electron paramagnetic resonance spectrum of its copper-doped crystals

Abstract

Crystals of the title complex [{Zn_3·5O(O₂CMe)₅(py)}₂](py = pyridine) are orthorhombic, space group Pbca, with unit-cell dimensions a= 16.598(3), b= 14.682(4), c= 19.111(9)Å, and Z= 4. The crystal and molecular structure has been determined from diffractometric data by the heavy-atom method and refined by least squares to R 0.076. Seven zinc atoms, bridged by acetate groups, form a heptameric centrosymmetrical unit. In each of the two semi-units a central oxygen is surrounded tetrahedrally by three zinc atoms which are in a tetrahedral arrangement, and by one zinc atom in a tetragonally compressed octahedral environment. The low-temperature e.s.r. spectrum of ⁶³Cu-doped crystals of the complex is reported. The paramagnetic ion is substituted at the compressed tetragonal zinc site. The g, metal hyperfine-coupling, and quadrupole-coupling tensors have been obtained from an analysis of the angular variation of the spectra. In spite of the low site symmetry indicated by the X-ray results, an almost pure d_z² ground state is found to be present. A small 4s admixture is assumed to be responsible for the reduced value of the isotropic part of the copper hyperfine tensor.