The alkoxido-titanium pentamolybdate [(iPrO)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(OiPr)4 in MeCN and has been characterised by 1H, 13C, 17O, 49Ti and 95Mo NMR and FTIR spectroscopy, electrospray ionisation mass spectrometry, elemental microanalysis and single-crystal X-ray crystallography. The Lindqvist-type structure is derived from [Mo6O19]2− by replacement of {Mo=O}4+ by {(iPrO)Ti}3+ and shows bond alternation in the TiMo3O4 rings, with average bond distances of 1.956(8) Å for Ti–O(Mo), 1.832(7) Å for Mo–O(Ti), 1.943(7) Å for Moeq–O(Moax) and 1.910(6) Å for Moax–O(Moeq), while the increase in charge results in a decrease in 17O NMR chemical shift for terminal Mo=O groups from δ 933 for [Mo6O19]2− to δ 875 and 857 for 1 and a shift in νMo=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)3 1 could be assigned to ion aggregates containing 1 or fragments derived from 1, including {(TBA)2[(iPrO)TiMo5O18]}−, {(TBA)[(iPrO)TiMo5O18]}2−, {(iPrO)TiMo2O8}−, {TiMo5O18}2−, {TiMo4O15}2− and {Mo3O10}2−.