Synthesis, crystal structures and magnetic properties of tricyanomethanide-containing copper(II) complexes

Abstract

The preparation, crystal structures and magnetic properties of the copper(II) complexes of formula [Cu(pyim)(tcm)₂]_n (1), [Cu(bpy)(tcm)₂]_n (2), [Cu₄(bpz)₄(tcm)₈] (3), {[Cu(terpy)(tcm)]·tcm}_n (4) and {[Cu₂(tppz)(tcm)₄]·3/2H₂O}_n (5) [pyim = 2-(2-pyridyl)imidazole, tcm = tricyanomethanide, bpy = 2,2′-bipyridine, bpz = 2,2′-bipyrazine, terpy = 2,2′:6′,2″-terpyridine and tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine] are reported. Complexes 1, 2 and 4 are uniform copper(II) chains with single- (1 and 4) and double-(2) µ-1,5-tcm bridges with values of the intrachain copper–copper separation of 7.489(1) (1), 7.520(1) and 7.758(1) (2) and 7.469(1) Å (4). Each copper atom in 1, 2 and 4 is five-coordinate with bidentate pyim (1)/bpy (2) and tridentate terpy (4) ligands and nitrile-nitrogen atoms from bridging (1, 2 and 4) and terminal (1) tcm groups building a distorted square pyramidal surrounding. The structure of 3 is made up of neutral centrosymmetric rectangles of (2,2′-bipyrazine)copper(II) units at the corners, the edges being built by single- and double-µ-1,5-tcm bridges with copper–copper separations of 7.969(1) and 7.270(1) Å, respectively. Five- and six-coordinated copper atoms with distorted square pyramidal and elongated octahedral environments occur in 3. Compound 5 is a neutral copper(II) chain with regular alternating bis-tridentate tppz and double µ-1,5-tcm bridges, the intrachain copper–copper distances being 6.549(7) and 7.668(1) Å, respectively. The two crystallographically independent copper atoms in 5 have an elongated octahedral geometry with three tppz nitrogen atoms and a nitrile-nitrogen atom from a bridging tcm group in the equatorial positions, and two nitrile nitrogen atoms from a terminal and a bridging tcm ligand occupying the axial sites. The investigation of the magnetic properies of 1–5 in the temperature range 1.9–295 K has shown the occurrence of weak ferro- [J = +0.11(1) cm⁻¹ (2)] and antiferromagnetic interactions [J = −0.093(1) (1), −0.083(1) (4), −0.04(1) and 1.21(1) cm⁻¹ (3)] across the µ-1,5-tcm bridges and intermediate antiferromagnetic coupling [−J = 37.4(1) cm⁻¹ (5)] through bis-tridentate tppz. The values of the magnetic interactions are analyzed through simple orbital symmetry considerations and compared with those previously reported for related systems.