Equilibria of mononuclear oxomolybdenum(VI) complexes of triethanolamine.: A multinuclear dynamic magnetic resonance study of structure and exchange mechanisms

1D and 2D 1H and 13C NMR spectra of the assumed [MoO4(TEA)]2− complex recorded in DMSO at variable temperatures clearly indicate one free and two bound hydroxyethyl arms. The free arm of the ligand readily exchanges with the two metal-bound arms. Under such conditions the triethanolamine (TEA) acts as a bidentate ligand. The presence of water accelerates the exchange, which at higher water content involves the free ligand too. In organic solvents the binding strength of the hydroxo groups to the molybdenum is weaker than that of the water molecules. A plausible structure is confirmed by 14N, 17O and 95Mo measurements and an exchange mechanism based on the existence of an eight-membered relatively rigid chelate ring is suggested.