Solid State Coordination Chemistry: One-, Two-, and Three-Dimensional Materials Constructed from Molybdophosphonate Subunits Linked through Binuclear Copper Tetra-2-pyridylpyrazine Groups

The hydrothermal reactions of MoO3, an appropriate Cu(II) source, tetra-2-pyridylpyrazine (tpypyz), and phosphoric acid and/or an organophosphonate yielded a series of organic-inorganic hybrid materials of the copper-molybdophosphonate family. A common feature of the structures is the entrainment within the extended architectures of chemically robust {Mo5O15(O3PR)2}4- clusters as molecular building blocks. The cluster is a characteristic feature of the one-dimensional materials [{Cu2(tpypyz)(H2O)3}Mo5O15(HPO4)(O3PCH2CO2H)]·H2O (1·H2O) and [{Cu2(tpypyz) (H2O)}Mo5O15(O3PC6H5)2]·2H2O (2·2H2O), the two-dimensional network [{Cu2(tpypyz)(H2O)3}Mo5O15(HPO4)2]·2H2O (5·2H2O) and the three-dimensional frameworks [{Cu2(tpypyz)(H2O)2}Mo5O15{O3P(CH2)nPO3}]·xH2O [n = 3, x = 2.25 (6·2.25H2O); n = 4, x = 0.33 (7·0.33H2O)]. In the case of methylenediphosphonate as the phosphorus component, the unique chelating nature of the ligand precludes formation of the pentamolybdate core, resulting in the chain structures [{Cu2(tpypyz)(H2O)}Mo3O8 (HO3PCH2PO3)2]·8H2O (3·8H2O) and [{Cu2(tpypyz)(H2O)}2(Mo3O8)2(O3PCH2PO3)3]·16.9H2O (4 ·16.9H2O). For structures 1-7, the secondary metal-ligand building block is the binuclear {Cu2(tpypyz)(H2O)x}4+ cluster. There is considerable structural versatility as a result of the variability in the number of attachment sites at the phosphomolybdate clusters, the coordination geometry of the Cu(II), which may be four-, five-, or six-coordinate, the extent of aqua ligation, and the participation of phosphate oxygen atoms as well as molybdate oxo groups in bonding to the copper sites.