Synthesis, crystal structure and magnetic properties of H2tppz[ReCl6] and [Cu(bpzm)2(μ-Cl)ReCl3(μ-ox)Cu(bpzm)2(μ-ox)ReCl3(μ-Cl)]n

Abstract

Two new Re(IV) compounds of formulae H₂tppz[ReCl₆] (1) and [Cu(bpzm)₂(μ-Cl)ReCl₃(μ-ox)Cu(bpzm)₂(μ-ox)ReCl₃(μ-Cl)]_n (2) [tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine and bpzm = bis(pyrazolyl-1-yl)methane] have been prepared and their crystal structures determined by X-ray diffraction on single crystals. Compound 1 is a mononuclear species whose structure consists of octahedral hexachlororhenate(IV) anions and diprotonated H₂tppz²⁺ cations which are arranged in the unit cell as alternating anionic and cationic layers, held together by electrostatic forces. The structure of 2 is made up of alternating [Cu(1)(bpzm)₂]²⁺ and [(ox)ReCl₃(μ-Cl)Cu(2)(bpzm)₂(μ-Cl)ReCl₃(ox)]²⁻ entities interlinked by oxalate bridges to afford a neutral heterobimetallic chain. The oxalate group adopts the didentate (at Re)/monodentate (at Cu) bridging mode. The magnetic behavior of 1 and 2 has been investigated over the temperature range 1.9–295 K. 1 is a magnetically diluted Re(IV) complex, the relatively large value of the zero-field splitting of the ground level [D = −15.8(2) cm⁻¹] accounting for the variation of χ_MT in the low temperature range. Weak intrachain ferromagnetic interactions between Re(IV) and Cu(II) through oxalate (J₁ = +0.15 cm⁻¹) and single chloro (J₂ = +4.9 cm⁻¹) bridges occur in 2 which are obscured by the large zero-field splitting of the Re(IV) ion (D_Re = 42 cm⁻¹). In addition, interchain antiferromagnetic interactions are also involved in 2 which are responsible for the metamagnetic behavior observed, the value of the critical dc magnetic field (H_c) being 20 kOe.