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

In the title salt, [Ni(C(26)H(24)P(2))(2)](CF(3)SO(3))(2) or [Ni(dppe)(2)](2+)·(OTf(−))(2) [dppe = 1,2-bis­(di­phenyl­phosphan­yl)ethane and OTf(−) = tri­fluoro­methane­sulfonate], the Ni atom (site symmetry [Image: see text]) 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.