Crystal structure of copper(II)mellitate, [Cu3.5C6(COO)5(COOH)(OH)2(H2O)8.5]·4.5H2O

The crystal structure of copper(II)mellitate, Cu_3.5C₁₂H₂₉O₂₇, has been determined by X-ray analysis. The complex crystallizes in the orthorhombic space groupIba2, with unit-cell dimensionsa=19.274(3),b=21.054(7),c=12.956(4) Å. The structure was deduced by the direct method with the help of the Patterson method and refined by the block-diagonal least-squares technique to a finalR value of 0.037 for 2995 observed reflections. Among six carboxyl groups of mellitic acid, five groups lose protons and form coordinate bonds to four copper atoms, and the remaining group forms hydrogen bonds to the water of crystallization and coordinated water. The configuration around copper is distorted-pyramidal, with the Cu-O bond distances of 1.896(7) to 2.425(7) Å.