Dicopper(II) complexes with N3,N4-bridging 1-alkyltetrazoles: Synthesis, crystal structure, magnetic and thermodynamic properties.

1-R-Tetrazoles (R ​= ​Et, i -Pr, t -Bu) were found to react with copper(II) tetrafluoroborate hexahydrate and copper(II) nitrate tetrahydrate giving the complexes [Cu 2 L 8 (H 2 O) 2 ]X 4 , where L ​= ​1-R-tetrazole, X ​= ​BF 4 − or NO 3 −. Single crystal X-ray analysis showed that the complexes comprised dinuclear cations [Cu 2 L 8 (H 2 O) 2 ]4+, with six tetrazole ligands showing monodentate N4-coordination, and two ones providing N3,N4 bridges between the copper(II) cations; water molecules complete the distorted octahedral coordination of metal ions. Magnetic susceptibility measurements revealed that the copper(II) ions were very weakly antiferromagnetically coupled. Сomplex [Сu 2 L 8 (H 2 O) 2 ](BF 4) 4 (L ​= ​1-isopropyltetrazole) was found to exhibit a temperature induced reversible single-crystal to single-crystal polymorphic phase transition. For this complex, adiabatic calorimetry was used to find the standard thermodynamic characteristics of this transition as well as the standard thermodynamic functions of the compound in the temperature range of 80–370 ​K. Additionally, mononuclear complex of the composition [CuL 6 ](BF 4) 2 (L ​= ​1-ethyltetrazole) was obtained during the investigation and structurally characterized. Dicopper(II) complexes with N3,N4-bridging coordination of 1-alkyltetrazoles show weak antiferromagnetic coupling. Complex with 1-isopropyltetrazole exhibits a temperature induced reversible single-crystal to single-crystal polymorphic phase transition for which standard thermodynamic functions were determined. [Display omitted] • Dicopper(II) complexes with N3,N4-bridging coordination of 1-alkyltetrazoles were synthesized and characterized by X-ray analysis. • Copper(II) ions is weakly antiferromagnetically coupled in dinuclear complexes. • Dicopper(II) complex with 1-isopropyltetrazole exhibits a temperature induced single-crystal polymorphic phase transition. • Standard thermodynamic functions of complex and its transition were determined by adiabatic calorimetry. [ABSTRACT FROM AUTHOR]