Synthesis, Crystal Structure, Magnetic Properties, and Theoretical Studies of [{Cu(mepirizole)Br}₂(μ-OH)(μ-pz)] (Mepirizole = 4-Methoxy-2-(5-methoxy-3-methyl-1<i>H</i>-pyrazol-1-yl)-6-methylpyrimidine; pz = Pyrazolate), a Novel μ-Pyrazolato−μ-Hydroxo-Dibridged Copper(II) Complex

A novel μ-pyrazolato−μ-hydroxo-dibridged copper(II) complex has been synthezised and structurally characterized: [{Cu(mepirizole)Br}2(μ-OH)(μ-pz)] (mepirizole = 4-methoxy-2-(5-methoxy-3-methyl-1H-pyrazol-1-yl)-6-methylpyrimidine; pz = pyrazolate). The title compound crystallizes in the monoclinic system, space group P21/c, with a = 15.618(2) Å, b = 15.369(3) Å, c = 16.071(3) Å, and β = 112.250(1)°. The structure is built up of dinuclear [{Cu(mepirizole)Br}2(μ-OH)(μ-pz)] units with five-coordinated copper(II) ions (CuBrN3O chromophores) linked by μ2-OH and μ2-pyrazolato bridges that are well separated from each others. The intramolecular copper−copper distance is 3.378(3) Å. Magnetic susceptibility data show that the copper atoms are strongly antiferromagnetically coupled with J = −770 cm-1. The obtained triplet−singlet energy gap is compared with those reported for a series of related dimers. The strong antiferromagnetic coupling arising from the complementarity of the hydroxo and pyrazolato bridges has been discussed on the basis of DFT calculations.