Abstract
The asymmetric unit of the title compound, trans-di-aqua-(1,4,8,11-tetra-aza-undecane-κ4 N 1,N 4,N 8,N 11)nickel(II) bis-(pyridine-2,6-di-carboxyl-ato-κ3 O 2,N,O 6)nickel(II) {[Ni(L)(H2O)2][Ni(pdc)2] where L = 1,4,8,11-tetra-aza-undecane (C7H20N4) and pdc = the dianion of pyridine-2,6-di-carb-oxy-lic acid (C7H3NO4 2-)} consists of an [Ni(L)(H2O)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 tetra-amine ligand and the mutually trans O atoms of the water mol-ecules in a tetra-gonally elongated octa-hedral 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 NiII ion is coordinated by the two tridentate pdc2- ligands via their carboxyl-ate and nitro-gen atom donors in a distorted octa-hedral trans-NiO4N2 geometry with nearly orthogonal orientation of the planes defining the carboxyl-ate 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 tetra-amine, the carb-oxy-lic groups of the pdc2- anion and the coordinated water mol-ecules are involved in numerous N-H⋯O and O-H⋯O hydrogen bonds, leading to electroneutral sheets oriented parallel to the (001) plane.
Highlights
Multidentate aromatic carboxylates are known as the most common linkers in MOFs (Rao et al, 2004)
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) A ]
The NiII ion is coordinated by the two tridentate pdc2– ligands via their carboxylate and nitrogen atom donors in a distorted octahedral trans-NiO4N2 geometry with nearly orthogonal orientation of the planes defining the carboxylate rings and the average Ni—N bond length [1.965 (4) A ] shorter than the average Ni—O bond distance [2.113 (7) A ]
Summary
Crystalline coordination polymers possessing permanent porosity (metal–organic frameworks, MOFs) are of enormous current interest because of their potential for applications in different areas including gas storage, separation, catalysis, etc. (MacGillivray & Lukehart, 2014; Kaskel, 2016). The bridging properties of one of the simplest representative of this class of compounds, 1,3-benzenedicarboxylate, with macrocyclic nickel(II) cations are well studied (see, for example, Tsymbal et al, 2021), coordination polymers based on its structural analogue, pyridine-2,6-dicarboxylate (C7H3NO42–; pdc2–), are confined to a sole example (Choi et al, 2003). An attempt to prepare a coordination polymer containing the [Ni(cyclam)]2+ cation with pdc2– led to the ionic product [Ni(cyclam)(H2O)2][Ni(pdc)2]Á2.5H2O due to sequestering of the metal ion from the cavity of the macrocycle by this chelating ligand (Park et al, 2007). As part of our research on MOFs formed by nickel(II) tetraaza cations and aromatic carboxylates, we report here the synthesis and crystal structure of the product of the reaction of [Ni(L)]2+ with pdc2–, namely [trans-diaqua(1,4,8,11-tetraazaundecane-k4N1N4N8N11)nickel(II)][bis(pyridine-2,6-dicarboxylato-3N,O,O)nickel(II)], [Ni(L)(H2O)2][Ni(pdc)2], I. To the best of our knowledge, the structure of the [trans-diaqua(1,4,8,11-tetraazaundecane)nickel(II)] moiety has not previously been reported in the literature
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