N-heterocycle chelated oxomolybdenum(VI and V) complexes with bidentate citrate

A 1,10-phenanthroline (phen) chelated molybdenum(VI) citrate, [(MoO2)2O(H2cit)(phen)(H2O)2]·H2O (1) (H4cit = citric acid), is isolated from the reaction of citric acid, ammonium molybdate and phen in acidic media (pH 0.5–1.0). A citrato oxomolybdenum(V) complex, [(MoO)2O(H2cit)2(bpy)2]·4H2O (2), is synthesized by the reduction of citrato molybdate with hydrazine hydrochloride in the presence of 2,2′-bipyridine (bpy), and a monomeric molybdenum(VI) citrate [MoO2(H2cit)(bpy)]·H2O (6) is also isolated and characterized structurally. The citrate ligand in the three neutral compounds uses the α-alkoxy and α-carboxy groups to chelate as a bidentate leaving the two β-carboxylic acid groups free, that is different from the tridentate chelated mode in the citrato molybdate(VI and V) complexes. 1 and 2 in solution show obvious dissociation based on 13C NMR studies.