Polyoxomolybdenum(V/VI)-sulfite compounds: Synthesis, structural, and physical studies

Abstract

Reaction of Na2MoVIO4·2H 2O with (NH4)2SO3 in the mixed-solvent system H2O/CH3CN (pH = 5) resulted in the formation of the tetranuclear cluster (NH4)4[Mo 4VISO16]·H2O (1), while the same reaction in acidic aqueous solution (pH = 5) yielded (NH4) 4[Mo5VIS2O21] ·3H2O (2). Compound {(H2bipy)2[Mo 5VIS2O21]·H 2O}x (3) was obtained from the reaction of aqueous acidic solution of Na2MoVIO4·2H2O with (NH4)2SO3 (pH = 2.5) and 4,4′-bipyridine (4,4′-bipy). The mixed metal/sulfite species (NH4)7[CoIII(Mo2VO 4)(NH3)(SO3)6]·4H 2O (4) was synthesized by reacting Na2Mo VIO4·2H2O with CoCl2· 6H2O and (NH4)2SO3 with precise control of pH (5.3) through a redox reaction. The X-ray crystal structures of compounds 1, 2, and 4 were determined. The structure of compound 1 consists of a ring of four alternately face- and edge-sharing MoVIO6 octahedra capped by the trigonal pyramidal sulfite anion, while at the base of the Mo4 ring is an oxo group which is asymmetrically shared by all four molybdenum atoms. Compound 3 is based on the Strandberg-type heteropolyion [Mo5VIS2O21]4-, and these coordinatively saturated clusters are joined by diprotonated 4,4′-H 2bipy2+ through strong hydrogen bonds. Compound 3 crystallizes in the chiral space group C2. The structure of compound 4 consists of a novel trinuclear [CoIIIMo2VSO 32-] cluster. The chiral compound 3 exhibits nonlinear optical (NLO) and photoluminescence properties. The assignment of the sulfite bands in the IR spectrum of 4 has been carried out by density functional calculations. The cobalt in 4 is a d6 octahedral low-spin metal atom as it was evidenced by magnetic susceptibility measurements, cw EPR, BVS, and DFT calculations. The IR and solid-state UV-vis spectra as well as the thermogravimetric analyses of compounds 1-4 are also reported. © 2007 American Chemical Society.