Thiohydrazide complexes of molybdenum and their relevance to reduction of dinitrogen to ammonia

Aqueous solution of sodium molybdate reacts with aromatic thiohydrazides like thiobenzhydrazide, 2-hydroxythiobenzhydrazide, furan-2-thiohydrazide and thiophen-2-thiohydrazide to form green, neutral diamagnetic 1 : 3 chelates. They were characterized by elemental analysis and spectroscopic methods. Tris(2-hydroxythiobenzhydrazido) molybdenum(VI) was crystallized from benzene and the crystal structure shows that molybdenum(VI) is hexacoordinated to three sulfur and three nitrogen atoms from three identical ligands in facile trigonal prismatic geometry. The OH group is involved in intramolecular and intermolecular hydrogen bonding. The bound ligands of tris(thiohydrazido) molybdenum(VI) undergo a redox reaction differently depending on the solvents. Two complexes of molybdenum bound to those oxidized ligands were isolated and characterized and their structures were also solved. Of them a binuclear complex, containing two MoO22+ ions, of the ligand N-2-hydroxybenzoyl-N'-2-hydroxythiobenzoyl-hydrazine showed some capability to catalyze the reduction of dinitrogen to ammonia by sodium borohydride.