Ligand-directed conformation of inorganic-organic molecular capsule and cage.

Four new inorganic-organic hybrids, namely, (NH4)3H3[AsMo6O21(O2CC6H4NH2)3]·8.5H2O (1), (NH4)16H3[(AsMo6O21)3(O2CCH2CO2)5]·18H2O (2), (NH4)11H[(AsMo6O21)2{O2C(CH2)6CO2}3]·8H2O (3), and (NH4)18H6[(AsMo6O21)4{C6H3(CO2)3}4]·24.5H2O (4), were synthesized by reaction of As2O3 with (NH4)6Mo7O24·4H2O and organic components in aqueous medium. All of the four hybrids feature a common {AsMo6} unit composed of a six-membered MoO6 octahedral ring capped by one {AsO3} trigonal pyramid. Although these hybrids exhibit similar chemical formula, their structures are monomer, dimer (capsule), trimer, and tetramer (cage), respectively, depending upon the nature of carboxylic acids. Also, the assembly processes appear to be highly versatile and sensitive to the inherent nature of carboxylic acids, which direct the assemblies toward construction of POM clusters and participate directly to their stabilization. In addition, successful isolation of these hydrids shows that it would be possible to achieve a variety of structural predesign in this inorganic-organic system by means of a ligand design route based on the interplay between the organic molecules and polyoxometalates (POMs).