REACTIONS OF MOO3 WITH DIETHYLENETRIAMINE (DIEN) - SYNTHESES, SOLID-STATE CHARACTERIZATION AND THERMAL-BEHAVIOR - MOLECULAR AND CRYSTAL-STRUCTURE OF A 2ND POLYMORPH OF (H3DIEN)2[MO7O24].4H2O

The reaction Of MoO3 with diethylenetriamine in aqueous solution yields four compounds: two polymorphs of bis(diethylenetriammonium) heptamolybdate(VI) tetrahydrate, (H3dien)2[Mo7O24].4H2O (1 and 2), bis(3-aza-1,5-pentamethylenediaminonium) octamolybdate(VI) hexahydrate, (H2dien)2[Mo8O26].6H2O (3), and the oxocomplex diethylenetriaminetrioxomolybdenum(VI), [MoO3(dien)] (4). The compounds were characterized by means of thermal analyses and IR spectroscopy. The crystal structure of 1 was determined by X-ray diffraction. Compounds 1 and 2 are an unprecedented case ot' polymorphism in discrete polyoxomolybdates and their syntheses experimentally confirm the ability of polyoxometallates to promote the stacking of a large number Of organic molecules by means of an extended network of hydrogen contacts. Both structures contain discrete[Mo7O24]6- polyanions, diethylenetriammonium cations and water molecules connected through hydrogen bonding interactions which are responsible for a different crystal packing in both compounds. In 1 the Mo(5)-O(17) bond length, 2.675(4) angstrom, is significantly longer than those observed for other organoammonium heptamolybdates that exhibit photochemical properties and antitumour activity. This long molybdenum oxygen distance may play an important role in the possible photochromism and anticancer activity of this compound.