Penta- and dinuclear carboxylate nickel(II) complexes with pyrazole-based ligands: Syntheses, magnetic properties and DFT calculations

Abstract

«One pot» reactions of pyrazole-based ligands Hdmpz and PyPz with in situ formed carboxylate precursors led to the formation of mono- and di-aqua-bridged binuclear compounds, as well as pentanuclear hydroxo-bridged compound: [Ni2(μ-OH2)(μ-O2CC(CH3)3)2(O2CC(CH3)3)2(PyPz)2]1, [Ni5(μ3-OH)2(μ-O2CPh)8(PyPz)4].4.73MeCN2, [Ni2(μ-OH2)(μ-O2CPh)2(O2CPh)2(Hdmpz)4]3, [Ni2(μ-OH2)2(μ-O2CPh)(O2CPh)2(Hdmpz)4](O2CPh)∙2.5H2O4 (Hdmpz = 3,5-dimethylpyrazole, PyPz = 2-(5-Methyl-1H-pyrazol-3-yl)pyridine). Compounds were characterized by structural and spectral methods, thermogravimetric analysis and magnetic measurements were also performed. It was noted, that structural motif of forming compounds are determined by the structure of carboxylate precursors formed in situ and properties of N-ligands. Comparison of magnetic measurements data, structural data, and DFT calculations allows us to conclude that in the case of investigated compounds the equilibrium between spin isomers with different multiplicities, close energy values and close geometrical structure can be realized.