The reaction of molten trimethylpyrazole (tmpzH) with copper metal shot in air yields a mixture of the trinuclear copper(I) complex [Cu(tmpz)]3, 1, and the trinuclear copper(I/II) complex [Cu(3-CO2dmpz)(tmpzH)]2Cu, 2 (where dmpz is dimethylpyrazolate). Crystals of 1 are monoclinic, a = 8.403(3), b = 22.453(2), c = 11.362(2) Å, (3 = 95.83(2)°, Z = 4, space group P21/c. Crystals of 2 are triclinic, a = 10.988(3), b = 11.009(2), c = 6.457(1) Å, α = 103.13(2)°, β = 103.02(2)°, γ = 108.70(2)°, Z = 1, space group [Formula: see text]. The reaction of molten 4-bromodimethylpyrazole (4-BrdmpzH) with copper metal shot in air gave the binuclear copper(II) complex [Cu(4-Br-3-CO)2mepz)(4-BrdmpzH)2]2, 3 (where mepz is methylpyrazolate). There are two crystalline forms of 3:3a, triclinic, a = 10.152(3), b = 13.068(3), c = 10.033(3) Å, a = 112.38(2)°, (3 = 116.46(2)°, γ = 70.29(2)°, Z = 1, space group [Formula: see text]; and 3b, monoclinic, a = 13.470(1), b = 16.005(2), c = 20.174(1) Å, β = 98.142(6)°, Z = 4, space group C2/c. Magnetic susceptibility studies on a bulk sample of 3 (2.0–300 K) revealed antiferromagnetic coupling between the double pyrazolate bridged copper centres and analysis of the data according to a Heisenberg model for coupled pairs of S = 1/2 metal ions gave −75.4 cm−1 for the value of the exchange coupling constant, J. The crystal structures of 1, 2, 3a, and 3b were solved by the Patterson method and were refined by full-matrix least-squares procedures to final R values of 0.036, 0.056, 0.042, and 0.042 for 2265, 1764, 2011, and 2575 reflections with I ≥ 3σ(I), respectively.

Ehlert, M. K., Rettig, S. J., Storr, A., Thompson, R. C., & Trotter, J. (1992). Polynuclear pyrazolate complexes of copper. Crystal and molecular structures of [Cu(tmpz)]3, [Cu(3-CO2dmpz)(tmpzH)]2Cu, and [Cu(4-Br-3-CO2mepz)(4-Br-dmpzH)2]2 (where mepz = methylpyrazolate, dmpz = dimethylpyrazolate, and tmpz = trimethylpyrazolate) and magnetic susceptibility studies on the dinuclear complex. Canadian Journal of Chemistry, 70(8), 2161–2173.