Synthesis and Structure of the Alkoxido-Titanium Pentamolybdate (IIBu4N)3[(iPrO)TiMo5O18]: An Entry into Systematic TiMo5 Reactivity

The alkoxido-titanium pentamolybdate [((PrO)-Pr-i)TiMo5O18](3-) (1) has been obtained as its tetrabutylammonium (TBA) salt by hydrolysis of a mixture containing (TBA)(2)[Mo2O7], (TBA)(4)[Mo8O26] and Ti((OPr)-Pr-i)(4) in MeCN and has been characterised by H-1, C-13, O-17, Ti-49 and Mo-95 NMR and FTIR spectroscopy, electrospray ionisation mass spectrometry, elemental microanalysis and single-crystal X-ray crystallography. The Lindqvist-type structure is derived from No6O19](2-) by replacement of (Mo=O)(4+) by {((PrO)-Pr-i)Ti}(3+) and shows bond alternation in the TiMo3O4 rings, with average bond distances of 1.956(8) angstrom for Ti-O(Mo), 1.832(7) angstrom for Mo-O(Ti), 1.943(7) angstrom for Mo-eq-O(Mo-ax) and 1.910(6) angstrom for Mo-ax-O(Mo-eq), while the increase in charge results in a decrease in 170 NMR chemical shift for terminal Mo=O groups from delta 933 for [Mo6O19](2-) to delta 875 and 857 for 1 and a shift in nu(Mo=O) from 951 cm(-1) for [Mo6O19](2-) to 930 cm(-1) for 1. The main peaks in the negative-ion electrospray ionisation mass spectrum of (TBA)31 could be assigned to ion aggregates containing 1 or fragments derived from 1, including {(TBA)(2)[(iPrO)TiMo5O18]}, {(TBA){((PrO)-Pr-i)TiMo5O18]}(2-), {((PrO)-Pr-i)TiMo2O8}(-) (TiMo5O18}(2-), (TiMo4O15}(2-) and (Mo3O10}(2-).