Crystal structure at 100 K of bis[1,2-bis(diphenylphosphanyl)ethane]nickel(II) bis(trifluoromethanesulfonate): a possible negative thermal expansion molecular material

Abstract

In the title salt, [Ni(C26H24P2)2](CF3SO3)2 or [Ni(dppe)2]2+·(OTf−)2 [dppe = 1,2-bis(diphenylphosphanyl)ethane and OTf− = trifluoromethanesulfonate], the Ni atom (site symmetry \overline{1}) 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.