Carboxylate-Functionalized Phosphomolybdates: Ligand-Directed Conformations

The
[HPMo6O21]2– units and carboxylate
linkers can be combined to build novel polyanions by a carefully designed
complementary system in self-assembly processes depending only on
the number of carboxyl groups and the nature of carboxylic acids.
Complexes (NH4)5[HPMo6O21(O2CC6H4OH)3]·4H2O (1), (NH4)8H2[(HPMo6O21)2(C2O4)3]·13H2O (2), (NH4)20[(HPMo6O21)4(O2CCH2CO2)6]·17H2O (3), and Cs2(NH4)10[(HPMo6O21)2(HPO3)­{C6H3(CO2)3}2]·5H2O (4) have been synthesized by
a simple one-pot reaction of (NH4)6Mo7O24·4H2O, H3PO3,
and carboxylic acid ligands in aqueous solution. Formation of these
compounds is critically dependent on the identifying carboxylic acids,
which play the important templated role in assembly processes. The
stability of these clusters was explored using electrospray ionization
mass spectrometry (ESI-MS) and 31P NMR spectroscopy, and
electron paramagnetic resonance (EPR) experiments further demonstrated
the result of the interesting photochromic property.