Markedly different magnetic properties of two analogous Ni(II) complexes with 2-aminoethylpyridine: [Ni(2aepy)2Cl(H2O)]Cl⋅H2O and [Ni(2aepy)2(NO3)]NO3

Abstract

By the reaction of nickel(II) chloride hexahydrate and nickel(II) nitrate hexahydrate with 2-aminoethylpyridine (2aepy) in the molar ratio 1:2 two complexes were isolated, namely [Ni(2aepy)2Cl(H2O)]Cl⋅H2O (1) and [Ni(2aepy)2(NO3)]NO3 (2). In both ionic complexes hexacoordinated Ni(II) central atoms exhibit heteroleptic coordination sphere formed by two chelate bonded 2aepy ligands and the remaining two coordination sites in cis positions are occupied by co-ligand(s), aqua and chlorido ligands in 1 and chelate bonded nitrato ligand in 2. In both crystal structures 1 and 2, medium strength hydrogen bonds led to formation of 2D hydrogen-bonded supramolecular structures. The study of the magnetic response in the temperature range 1.8–300 K and ab initio calculations in 1 revealed that the system can be considered as a rare candidate to study the behavior of anisotropic S = 1 antiferromagnetic spin chain close to the quantum-critical point defined by the ratio of the single-ion anisotropy and exchange interaction, which was estimated as D/J = 1.14 for 1. On the other hand, the coordination of nitrate ligand to the central Ni(II) ion in 2 yields a substantial change of the nature of anisotropy from easy-plane to easy-axis type with D/kB = −5.7 K and suppression of the exchange interaction between the Ni(II) centers.