Different conformations of two polyoxomolybdates functionalized by the same V shape carboxylic acid

In this study, two carboxylic acid-functionalized arsenomolybdates, namely, (NH4)15H6[(AsMo6O21)2 (AsMo6O23) (PDA)4]·21H2O (1), and Cs5Na8H13 [(AsMo6O21)4(PDA)7]·32H2O (2). (H2PDA = pyridine-2,6-dicarboxylic acid) have been synthesized and characterized. On account of the flexibility of the ligand H2PDA, compound 1 presented as a trimer, and compound 2 was a tetramer. This tetramer conformation is quite unique in carboxylic acid-functionalized polyoxomolybdates. Photochromic properties of the two compounds have been investigated, and both of them could change their color within 5 min under the irradiation of a Xe lamp. The thermochromic study were also conducted, and the two compounds changed the color at about 373 K. The EPR test indicated that the two kinds of allochromatic process were both related to the reduction of MoVI (4d0) to MoV (4d1).