Pentachloro(pyrazine)rhenate(iv) complex as precursor of heterobimetallic pyrazine-containing ReIV2MII (M = Ni, Cu) species: synthesis, crystal structures and magnetic properties.

Three novel Re(iv) mononuclear complexes of formulae NBu4[ReCl5(pyz)] (1), NH2Me2[ReCl5(pyz)] (2) and NH4[ReCl5(pyz)]·0.75H2O (3), (pyz being pyrazine; NBu4+ = tetra-n-butylammonium cation, NH2Me2+ = dimethylammonium cation and NH4+ = ammonium cation), were synthesized by ligand substitution reaction from [ReCl6]2− anion and pyrazine in N,N-dimethylformamide (DMF). In addition, two new heterobimetallic compounds, the salt namely [ReCl5(pyz)]2[Ni(cyclam)] (4) (cyclam = 1,4,8,11-tetraazacyclotetradecane) and the heterotrinuclear [{ReCl5(μ-pyz)}2Cu(DMF)4] (5) complex, were prepared by using as precursor 1 and 3, respectively. Compounds 1–5 were characterized by single-crystal X-ray diffraction. 1–3 are made up of discrete [ReCl5(pyz)]− anions and NBu4+ (1), NH2Me2+ (2) and NH4+ (3) cations. [ReCl5(pyz)]− unit interacts toward Ni(ii) (4) and Cu(ii) (5) metal ions through different modes. In 4 two [ReCl5(pyz)]− anions weakly interact with a [Ni(cyclam)]2+ cation through chloro atoms, while compound 5 is a heterotrinuclear pyrazine-bridged ReIV2CuII complex made up of [ReCl5(pyz)]− anions and [Cu(DMF)4]2+ cations. The magnetic properties of 1–5 were investigated in the temperature range 1.9–300 K. The magnetic behaviour of 1 is that of a magnetically diluted Re(iv) complex with a large value of zero-field splitting of the ground state (|2D| is ca. 18.8(1) cm−1), whereas those of 2 and 3 are typical of antiferromagnetically coupled systems exhibiting susceptibility maxima at 10 (2) and 12 K (3). Compound 4 shows antiferromagnetic interactions between Re(iv) metal ions, Ni(ii) being diamagnetic (because of its square-planar geometry), while 5 exhibits a ferromagnetic coupling between Re(iv) and Cu(ii) metal ions across the pyrazine bridges with a JReCu value of +11.8(1) cm−1. [ABSTRACT FROM AUTHOR]