Supramolecular architecture of metal-organic frameworks involving dinuclear copper paddle-wheel complexes

The two centrosymmetric dinuclear copper paddle-wheel complexes tetrakis(mu-4-hydroxybenzoato-kappa O-2:O')bis[aqua-copper(II)] dimethylformamide disolvate dihydrate, [Cu-2(C7H5O3)(4)(H2O)(2)]center dot 2C(3)H(7)NO center dot 2H(2)O, (I), and tetrakis(mu-4-methoxybenzoato-kappa O-2:O')bis[(dimethylformamide-kappa O)copper(II)], [Cu-2(C8H7O3)(4)(C3H7NO)(2)], (II), crystallize with half of the dinuclear paddle-wheel cage unit in the asymmetric unit and, in addition, complex (I) has one dimethylformamide (DMF) and one water solvent molecule in the asymmetric unit. In both (I) and (II), two Cu-II ions are bridged by four syn,syn-eta(1):eta(1):mu carboxylate groups, showing a paddle-wheel cage-type structure with a square-pyramidal coordination geometry. The equatorial positions of (I) and (II) are occupied by the carboxylate groups of 4-hydroxy- and 4-methoxy-benzoate ligands, and the axial positions are occupied by aqua and DMF ligands, respectively. The three-dimensional supramolecular metal-organic framework of (I) consists of three different R-2(2)(20) and an R-4(4)(36) ring motif formed via O-H center dot center dot center dot O and OW-HW center dot center dot center dot O hydrogen bonds. Complex (II) simply packs as molecular species.