Nickel(II) complexes with N,N,O-donor Schiff bases. Self-assembly to two-dimensional network via hydrogen bonding

The syntheses, characterization and crystal structures of two mononuclear nickel(II) complexes are described. Reactions of Ni(O₂CCH₃)₂⋅4H₂O with the Schiff bases derived from 2-pyridinecarbaldehyde and ortho-aminophenol (Hpaap) and 2-pyridinecarbaldehyde and ortho-aminobenzoic acid (Hpaab) in methanolic media afford the complexes in good yields. The elemental analysis, magnetic moments, and spectral features of the complexes are consistent with the formulae Ni(paap)₂]⋅CH₃COOH⋅H₂O and Ni(paab)₂]⋅2H₂O. Crystal data for Ni(paap)₂]⋅CH₃COOH⋅H₂O: monoclinic, P2₁/c, a = 9.675(2) Å, b = 17.109(5) Å, c = 14.403(4) Å, β = 92.903(11)^∘, V = 2381.1(11) ų, and Z = 4 and for Ni(paab)₂]⋅2H₂O: triclinic, P 1, a = 9.834(3) Å, b = 11.319(3) Å, c = 13.130(4) Å, α = 84.68(3), β = 67.54(3), γ = 85.49(2)^∘, V = 1343.4(6) ų, and Z = 2. In each complex, two tridentate monoanionic meridionally spanning ligands form a distorted octahedral N₄O₂ coordination sphere around the metal ion. In Ni(paap)₂]⋅CH₃COOH⋅H₂O, two metal coordinated phenolate-O atoms are hydrogen bonded to CH₃COOH and H₂O, respectively. Intramolecular C–H⋅ < eqid1 > ⋅O interactions involving the water molecule and the C–H from azomethine and aromatic fragments lead to a two-dimensional network of Ni(paap)₂]⋅CH₃COOH⋅H₂O in the crystal lattice. An uncoordinated carboxylate O-atom in Ni(paab)₂]⋅2H₂O is hydrogen bonded to both water molecules. One of the water molecules is again hydrogen bonded to the corresponding symmetry related water molecule forming a dimer. The azomethine groups and the metal coordinated carboxylate-O atoms in Ni(paab)₂] are involved in intermolecular C–H⋅ < eqid2 > ⋅O interactions forming a chain-like arrangement of the molecules. The water dimers act as bridges between these chains and a two-dimensional network of Ni(paab)₂]⋅2H₂O is formed.