Synthesis, crystal structure and magnetic properties of the complex [ReCl3(tppz)]·MeCN

Abstract

The reaction of the starting materials [Re^IIICl₃(MeCN)(PPh₃)₂] or [Re^VOCl₃(PPh₃)₂] with 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz) in acetonitrile yielded the Re(III) complex [ReCl₃(tppz)]·MeCN (1). This complex crystallizes in the monoclinic space group P2₁/n and its crystal structure consists of neutral mononuclear entities with meridional geometry of the chloride ligands, and the six-coordination of the Re(III) ion being completed by the tridentate tppz ligand. Each metal centre exhibits a highly distorted octahedral coordination with Re–Cl and Re–N_tppz bond lengths covering the ranges 2.3590(9)–2.3606(8) and 1.971(2)–2.096(2) Å, respectively. The magnetic properties of 1 have been investigated in the temperature range 1.9–290 K. They are characteristic of a six-coordinate Re(III) mononuclear complex with d⁴ low-spin (³T₁ ground state). The magnetic data of 1 are discussed through a deep analysis of the influence of the ligand-field, spin–orbit coupling, tetragonal distortion and covalency effects. The second-order Zeeman effect between the non-magnetic ground state (M_J = 0) and higher energy levels (M_J ≠ 0) determines the magnetic susceptibility of 1, the value of the temperature-independent paramagnetic susceptibility being 3378 × 10⁻⁶ cm³ mol⁻¹. This value compares well with those reported for other structurally characterized Re(III) complexes.