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).