Crystal Engineering of Polyoxomolybdates Based Metal–Organic Solids: The Case of Chromium Molybdate Cluster Based Metal Complexes and Coordination Polymers

Six new metal complex or coordination polymer incorporated Anderson–Evans cluster based solids, (H24-pyc)2[{Na(4-pyc)2}{CrMo6(OH)8O16}]·4H2O, 9, (H24-pyc)2[{Ni(4-pyc)2(H2O)4}{CrMo6(OH)7O17}]·10H2O, 12, (H23-pyc)2[{Na(3-pyc)2}{CrMo6(OH)8O16}]·2H2O, 13, and [{M2(2-pzc)2(H2O)4}{CrMo6(OH)7O17}]·17H2O (M = Co, 14 and Cu, 15; 4-pyc = pyridine-4-carboxylate, 3-pyc = pyridine-3-carboxylate, and 2-pzc = pyrazine-2-carboxylate) were crystallized in aqueous solution at room temperature. 9 shows alternating Anderson–Evans cluster and sodium complex {Na(4-pyc)2} coordinately linked forming one-dimensional (1-D) chains and free protonated H4-pyc moieties occur in between. 10 and 12 show the aggregation of a discrete Anderson–Evans cluster, metal complex, {M(4-pyc)2(H2O)4} (M = Ni and Cu), free protonated H4-pyc moieties, and water through extensive nonbonding interactions. Crystallization in the presence of H3-pyc, an isomer of H4-pyc yielded only a sodium based solid, (H23-pyc)2[{Na(3-pyc)2}{CrMo6(OH)8O16}]·2H2O, 13; it forms a chain similar to 9. However, nonbonding interactions that stabilize the chains are different. Reaction with 2-pzc resulted in two isostructural solids, [{M2(2-pzc)2(H2O)4}{CrMo6(OH)7O17}]·17H2O (M = Co, 14 and Cu, 15). 14 and 15 are the first examples where the coordination polymer is coordinated to an Anderson–Evans cluster. This paper is an attempt to understand the structural landscape of the system {M(H2O)n}2+-organic ligand-{HmCrMo6O24}n−. A retrosynthetic analysis of the isolated crystalline solids from the system provides molecular insights to interpret the crystal engineering of these complex materials and directions for designing new solids in the system.