Crystal structure and thermal properties of a square-planar Ni-II complex of cyanide and a tricyclic bis-amidine ligand formed in situ under solvothermal conditions.

The reaction of N-1,N-1′-(ethane-1,2-diyl)bis(propane-1,3-di-amine) (bapen), K-2[Ni(CN)(4)]center dot H2O and dimethylformamide in the presence of Gd(NO3)(3)center dot 6H(2)O under solvothermal conditions yielded yellow crystals of dicyanido(2,3,4,6,7,9,-10,11-octahydropyrimido[2′,1′:3,4]pyrazino[1,2-a]pyrimidine)-rimidine)nickel(II) hemihydrate, [Ni(CN)(2)(C10H16N4)]center dot 0.5H(2)O, (I), the crystal structure of which is composed of [Ni(CN)(2)(pdpm)] molecules (pdpm is 2,3,4,6,7,9,10,11-octahydropyrimido[2′,1′:3,4]pyrazino[1,2-a]pyrimidine) on general positions linked by O-H center dot center dot center dot N hydrogen bonds to water molecules located on twofold axes. This structural unit is further linked by nonclassical C-H center dot center dot center dot N interactions to form a warped two-dimensional net perpendicular to the unit-cell b axis. The nets are stacked, with C-H center dot center dot center dot O contacts joining successive units. The Ni II cation is coordinated with square-planar geometry by a chelating pdpm ligand and two cyanide ligands in mutually cis positions. Complex (I) is stable up to 360 K, at which point dehydration takes place; the ligands start to decompose at 558 K.