Pseudopolymorphism in Nickel(II) Complexes with 6-Methylpicolinate. Synthesis, Structural, Spectroscopic, Thermal, and Density Functional Theory Studies

Abstract

The reaction between 6-methylpicolinic acid (6-MepicH) and nickel(II) nitrate hexahydrate afforded a new octahedral complex containing two bidentate ligands and two water molecules in cis positions, which crystallized in two pseudopolymorphs, [Ni(6-Mepic)2(H2O)2]·2H2O (1) with cocrystallized water molecules from water solution and [Ni(6-Mepic)2(H2O)2] (2) without cocrystallized water. In 1, two molecules of nickel(II) complex are assembled in centrosymmetric dimers by three hydrogen bonds, which form a two-dimensional network by means of water molecules. These layers interact through π···π stacking arrangements between pyridine rings in the third dimension. In 2, centrosymmetric dimers held together by hydrogen bonds form two parallel chains and assemble in a three-dimensional network by π···π stacking. Density functional theory (DFT) calculations (ADF) performed on model dimers showed the major role of the O−H···O hydrogen bonds in establishing the whole network, without requiring large distortions from ...