Mononuclear anionic AO(2)X(3) compounds with non-VSEPR structure.

The molybdenyl compound [NBu4][MoO2(C6F5)3] () has been obtained by low-temperature treatment of MoO2Cl2 with LiC6F5 in Et2O followed by addition of [NBu4]Br. This compound of the (AO2X3)(-) type shows an unusual five-coordinate structure not lying in the Berry-pseudorotation path: it can be described rather as an edge-capped tetrahedron (TE-5). The same kind of structure has been found by DFT calculations to be the most energetically favored for the mononuclear (MoO2X3)(-) model species, where X = H, Cl or CN. Compound exhibits marked stereochemical stability, as it shows no sign of exchange between chemically inequivalent C6F5 groups even at 150 °C in dmf solution ((19)F NMR spectroscopy).