The crystal structure of szenicsite, Cu 3 MoO 4 (OH) 4 , orthorhombic, a = 8.5201(8), b = 12.545(1), c = 6.0794(6) Aa, V = 649.8(2) Aa 3 , space group Pnnm, Z = 4, has been solved by direct methods and refined by least-squares techniques to an agreement index (R) of 3.34% and a goodness-of-fit (S) of 1.11 for 686 unique observed [F > or = 4sigma F ] reflections collected using graphite-monochromated Mo-Kalpha X-radiation and a CCD area detector. The structure contains three unique Cu (super 2+) positions that are each coordinated by six anions in distorted octahedral arrangements; the distortions of the octahedra are due to the Jahn-Teller effect associated with a d 9 metal in an octahedral ligand-field. The single unique Mo (super 6+) position is tetrahedrally coordinated by four O (super 2-) anions. The Cu (super 2+) phi 6 (phi : unspecified ligand) octahedra share trans edges to form rutile-like chains, three of which join by the sharing of octahedral edges to form triple chains that are parallel to [001]. The MoO 4 tetrahedra are linked to either side of the triple chain of Cu (super 2+) phi 6 octahedra by the sharing of two vertices per tetrahedron, and the resulting chains are cross-linked through tetrahedral-octahedral vertex sharing to form a framework structure. The structure of szenicsite is closely related to that of antlerite, Cu 3 SO 4 (OH) 4 , which contains similar triple chains of edge-sharing Cu (super 2+) phi 6 octahedra.

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