Tetrakis(2,2′-bipyridine)di-μ3-hydroxido-bis(μ-2-oxidobenzoato)tetracopper(II) dinitrate tetrahydrate

The tetranuclear title complex, [Cu4(C7H4O3)2(OH)2(C10H8N2)4](NO3)2·4H2O, has a crystallographically imposed centre of symmetry. The CuII atoms display a distorted square-pyramidal coordination geometry and are linked by two μ2-phenolate O atoms from the salicylate ligands and two μ3-hydroxo groups, forming a Cu4O4 core that adopts a `stepped-cubane' geometry. In the crystal, the cations are linked by O—H...O hydrogen bonds to the nitrate anions, which are in turn connected via O—H...O interactions to centrosymmentric water tetramers