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

Abstract

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 Re^IV₂Cu^II 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 J_ReCu value of +11.8(1) cm⁻¹.