Crystal structure of trans-di­aqua­(1,4,8,11-tetra­aza­undeca­ne)nickel(II) bis­(pyridine-2,6-di­carboxyl­ato)nickel(II)

The asymmetric unit of the title compound, trans-di­aqua­(1,4,8,11-tetra­aza­undecane-κ(4) N (1),N (4),N (8),N (11))nickel(II) bis­(pyridine-2,6-di­carboxyl­ato-κ(3) O (2),N,O (6))nickel(II) {[Ni(L)(H(2)O)(2)][Ni(pdc)(2)] where L = 1,4,8,11-tetra­aza­undecane (C(7)H(20)N(4)) and pdc = the dianion of pyridine-2,6-di­carb­oxy­lic acid (C(7)H(3)NO(4) (2−))} consists of an [Ni(L)(H(2)O)(2)](2+) complex cation and a [Ni(pdc)(2)](2–) anion. The metal ion in the cation is coordinated by the four N atoms of the tetra­amine ligand and the mutually trans O atoms of the water mol­ecules in a tetra­gonally elongated octa­hedral geometry with the average equatorial Ni—N bond length slightly shorter than the average axial Ni—O bond [2.087 (4) versus 2.128 (4) Å]. The ligand L adopts its energetically favored conformation with five-membered and six-membered chelate rings in gauche and chair conformations, respectively. In the complex anion, the Ni(II) ion is coordinated by the two tridentate pdc(2–) ligands via their carboxyl­ate and nitro­gen atom donors in a distorted octa­hedral trans-NiO(4)N(2) geometry with nearly orthogonal orientation of the planes defining the carboxyl­ate rings and the average Ni—N bond length [1.965 (4) Å] shorter than the average Ni—O bond distance [2.113 (7) Å]. In the crystal, the NH donor groups of the tetra­amine, the carb­oxy­lic groups of the pdc(2–) anion and the coordinated water mol­ecules are involved in numerous N—H⋯O and O—H⋯O hydrogen bonds, leading to electroneutral sheets oriented parallel to the (001) plane.