Anhydrous CuC 4 O 4 , a Channel Structure solved from X–ray Powder Diffraction Data

The crystal structure of the new anhydrous metal squarate CuC 4 O 4 was solved from laboratory X–ray powder diffraction data. It crystallizes in the monoclinic space group I 2/ a (no. 15) with the lattice parameters a = 5.6747(1), b = 8.9394(4), c = 9.4987(4) Å und β = 94.372(2)° at ambient conditions (Z = 4, R F 2 = 8.24 %). The crystal structure can be reduced to a defect variant of the AlB 2 type of structure ([C 4 O 4 ][Cu □] ⇔ [Al][B 2 ]) and shows channels parallel to the a axis with a free diameter of about 2.3Å. The squarate dianion, [C 4 O 4 ] 2− , is acting as a μ 6 –ligand, in this case.