Crystal structure at 100†K of bis-[1,2-bis-(di-phenyl-phosphan-yl)ethane]-nickel(II) bis-(tri-fluoro-methane-sulfonate): a possible negative thermal expansion mol-ecular material.

In the title salt, [Ni(C26H24P2)2](CF3SO3)2 or [Ni(dppe)2]2+·(OTf-)2 [dppe = 1,2-bis-(di-phenyl-phosphan-yl)ethane and OTf- = tri-fluoro-methane-sulfonate], the Ni atom (site symmetry ) has a square-planar geometry with the bidentate ligands chelating the metal. As a result of the steric hindrance of the phenyl rings, the counter-ions are blocked from the metal coordination sphere. The dynamic disorder of the anion existing at 296 K is reduced at 100 K and based on these two temperatures, negative thermal expansion behaviour is observed.

High pressure Raman scattering study on Sm2Mo4O15 system.

High-pressure Raman experiments were performed on Sm2Mo4O15 system up to 7.9GPa. We show that this system exhibits an irreversible structural amorphization at 5.0GPa. In contrast to any other molybdates and tungstates experiencing pressure-induced amorphization, this structural change in Sm2Mo4O15 has strongly first-order character. This amorphous phase can be originated from the hindrance of a crystalline structural phase transition from the P1¯ to P2/m structure. Additionally, the assignment of Raman modes of the ambient-pressure phase of Sm2Mo4O15 was proposed based on lattice dynamics calculations.