Synthesis, crystal structure and magnetic properties of cyanide-bridged one-dimensional Ni(II)–Fe(III) complexes based on pentacyanoferrite

Crystal structure of trans-di-aqua-(1,4,8,11-tetra-aza-undeca-ne)nickel(II) bis-(pyridine-2,6-di-carboxyl-ato)nickel(II)

The coordination polyhedra of the nickel(II) ions of the title compound in the complex cation and the anion, viz., trans-NiN₄O₂ and trans-NiO₄N₂, are distorted octa­hedra. In the crystal, the donor groups of the tetra­amine and the coordinated water mol­ecules and the carboxyl­ate groups of the pyridine-2,6-di­carboxyl­ate anions are involved in numerous N—H⋯O and O—H⋯O hydrogen bonds, thereby forming sheets of ions lying parallel to the (001) plane.

The asymmetric unit of the title compound, trans-di­aqua­(1,4,8,11-tetra­aza­undecane-κ⁴N¹,N⁴,N⁸,N¹¹)nickel(II) bis­(pyridine-2,6-di­carboxyl­ato-κ³O²,N,O⁶)nickel(II) {[Ni(L)(H₂O)₂][Ni(pdc)₂] where L = 1,4,8,11-tetra­aza­undecane (C₇H₂₀N₄) and pdc = the dianion of pyridine-2,6-di­carb­oxy­lic acid (C₇H₃NO₄²⁻)} 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 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-NiO₄N₂ 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.

Heterotrimetallic Ni2Ln2Fe3 chain complexes based on [Fe(1-CH3im)(CN)5]2

Two phenoxo- and cyanido-bridged one-dimensional complexes Ni^II₂Gd^III₂Fe^III₃ (1) and Ni^II₂Dy^III₂Fe^III₃ (2) have been prepared. They are the first pentacyanidoferrite-bridged heterotrimetallic complexes. Magnetic studies reveal that overall ferromagnetic interactions are present in complexes 1 and 2, and complex 2 shows single-molecule magnet (SMM) behaviour with an energy barrier of 14.8 K.