Combined theoretical and mass spectrometry study of the formation-fragmentation of small polyoxomolybdates.

We investigate the assembly of small polyoxomolybdates using Car-Parrinello molecular dynamics simulations which show that there is an expansion of the coordination sphere of the Mo center from four to six in molybdate anions when the acidity of the solution is increased. With the help of complementary static density functional theory (DFT) calculations and electrospray ionization mass spectrometry experiments, we are able to postulate tentative mechanisms, with energy-cascade profiles, for the formation of the Lindqvist [Mo(6)O(19)](2-) anion. Similar to the family of isopolytungstates, it can be proposed that the [Mo(6)O(19)](2-) is formed by the aggregation of one molybdenum unit at a time; however, significant differences with respect to isopolytungstates are also found. The different behavior of chromates with respect to molybdates and tungstates is also considered.