Two Different Compounds Formed from Copper(II) tetrafluoridoborate and [1,2,4]triazolo[1,5-a]pyrimidine. Synthesis, Spectroscopy and Single-Crystal Structures

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Synthesis, crystal structure, spectroscopic and magnetic properties of an unprecedented tridimensional Cu(II) coordination compound of 1,2-bis(1,2,4-triazol-4-yl)ethane

A novel three-dimensional copper(II) compound of the formula [Cu3(btre)5(H2O)2](ClO4)6·H2O (btre = 1,2-bis(1,2,4-triazol-4-yl)ethane) has been synthesized. The structure has been solved at 150 K by single-crystal X-ray analysis. The compound [C30H44Cu3N30O2·6(ClO4)·H2O] crystallizes in the triclinic space group P1bar with a = 12.488(1), b = 13.195(1), c = 19.756(2) Å, α = 78.959(8), β = 84.553(8), γ = 63.869(7)°, V = 2868.4(5) Å3, Z = 2 (trinuclear CuII units), 6484 reflections [I > 4σ(I)], RF = 0.0581, wR2 = 0.1214. The structure of this coordination polymer consists of a three-dimensional network built up from linear trinuclear CuII cations of formula [Cu3(btre)5(H2O)2]6+. This crystallographically independent unit comprises a linear array of three CuII ions linked by triple N1,N2-1,2,4-triazole bridges, yielding Cu1–Cu2 = 3.893(1) Å and Cu2–Cu3 = 3.889(1) Å. These linear trinuclear CuII units are linked by various pathways involving tridentate and tetradentate bridging btre ligands, which yields an unprecedented three-dimensional network. The CuII ions are weakly antiferromagnetically coupled with J = –1.01(2) cm–1 (based on the Hamiltonian: H = –J[SCu1·SCu2 + SCu2·SCu3] using the expression for the molar magnetic susceptibility S = 1/2 of a linear trinuclear system). The nature and the magnitude of the antiferromagnetic exchange have been discussed on the basis of the structural features