Crystal structure and thermal properties of a square-planar NiIIcomplex of cyanide and a tricyclic bis-amidine ligand formedin situunder solvothermal conditions

Abstract

The reaction ofN1,N1′-(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-cellbaxis. The nets are stacked, with C—H...O contacts joining successive units. The NiIIcation is coordinated with square-planar geometry by a chelating pdpm ligand and two cyanide ligands in mutuallycispositions. Complex (I) is stable up to 360 K, at which point dehydration takes place; the ligands start to decompose at 558 K.