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-diamine) (bapen), K2[Ni(CN)4]·H2O and dimethylformamide in the presence of Gd(NO3)3·6H2O 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)nickel(II) hemihydrate, [Ni(CN)2(C10H16N4)]·0.5H2O, (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···N hydrogen bonds to water molecules located on twofold axes. This structural unit is further linked by nonclassical C-H···N interactions to form a warped two-dimensional net perpendicular to the unit-cell b axis. The nets are stacked, with C-H···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.