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 N¹,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.