Distinct supramolecular assemblies of nickel(II) complexes constructed from N-(4-pyridylmethyl)-l-amino acid derivatives: Synergistic effects of substituent groups and counter anions

Abstract

Four Ni(II) reduced Schiff base complexes, {[Ni(L1)(HCOO)(H2O)](H2O)} (1), {[Ni(L2)(H2O)3](OAc)} (2), {[Ni(L3)(H2O)3](OAc)} (3) and {[Ni(L4)(HCOO)](H2O)} (4), have been synthesized by the reaction of N-(4-pyridylmethyl)-l-amino acid derivatives and Ni(OAc)2·4H2O under hydrothermal conditions. Single-crystal X-ray diffraction analysis reveals all of the four Ni(II) centers in these complexes adopt a six-coordinated octahedral geometry, with complexes 1–3 uniformly crystallizing in the monoclinic P21 space group and 4 in the P212121 space group. A detailed structural study indicates the synergistic effects of the counteranions and steric hindrance of the substituents of the amino ligands lead to the formation of two different dimensionalities of the four compounds, with complexes 1 and 4 featuring 2D layer structures while complexes 2 and 3 exhibiting 1D chain structures. The resulting 3D supramolecular networks are formed by strong hydrogen bonding (OH⋯O and NH⋯O) interactions between the ligands and the guest molecules. The thermal stability, infrared spectra and luminescence properties of these compounds have also been investigated.