Structure And Polymorphism In M(ethylenediamine)3MoS4 (M = Mn, Co, Ni)

Polymorphism in hybrid inorganic-organic materials has not been explored as extensively as that in organic compounds, yet differences in solid-state structure can significantly affect the physical properties central to application of these materials. A new polymorph of Ni(en)(3)MoS4 (en = ethylenediamine), a hydrodesulfurization catalyst precursor, has been synthesized solvothermally and structurally characterized by single-crystal X-ray diffraction. The new structure (2) assumes the orthorhombic Pcab space group with a = 14.020(5) angstrom, b = 14.821(7) angstrom, and c = 16.230(6) angstrom. The structure of a polymorph that had been found previously (1) was redetermined at 100 K, confirming the orthorhombic Pna2(1) structure with a=15.916(13) angstrom, b = 7.610(3) angstrom, and c = 14.093(6) angstrom. Solvothermal reaction conditions including temperature, solvent water content, and nickel source were important in controlling polymorph formation. Differential scanning calorimetry and solvent-mediated conversion studies were used to compare the stabilities of the two nickel-containing polymorphs. The system was characterized as enantiotropic, with 2 favored at ambient temperature and I favored at 120 degrees C. However, kinetic factors are influential in the intermediate temperature range, and conversion is kinetically hindered under certain conditions. The new structures Co-(en)(3)MoS4 (3) and Mn(en)(3)MoS4 (4) were determined through single-crystal methods to be isostructural to 2. Compounds 1-4 were also characterized by elemental analysis, infrared spectroscopy, variable-temperature magnetic susceptibility measurements, and thermogravimetric analysis