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 cop-per(II) nitrate tetrahydrate giving the complexes [Cu2L8(H2O)(2)]X-4, where L = 1-R-tetrazole, X = BF4 or NO3. Single crystal X-ray analysis showed that the complexes comprised dinuclear cations [Cu2L8(H2O)(2)](4+), with six tetrazole ligands showing monodentate N4-coordination, and two ones providing N-3,N-4 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. Complex [Cu2L8(H2O)(2)](BF4)(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 func-tions of the compound in the temperature range of 80-370 K. Additionally, mononuclear complex of the composition [CuL6](BF4)(2) (L = 1-ethyltetrazole) was obtained during the investigation and structurally characterized.