Synthesis, crystal structure and magnetic properties of a linear trinuclear copper(II) compound with chloride and 4-amino-3,5-bis(hydroxymethyl)-1,2,4-triazole as bridging ligands

Abstract

A new linear trinuclear copper(II) co-ordination compound of the formula [Cu₃(H₂ahmt)₆Cl₄]Cl₂, where H₂ahmt = 4-amino-3,5-bis(hydroxymethyl)-1,2,4-triazole, has been synthesized. The crystal and molecular structure has been solved at 298 K by single-crystal X-ray analysis. The compound crystallizes in the triclinic space group P, with a= 10.2233(2), b= 9.2247(2), c= 13.6153(2)Å, α= 113.1441(2), β= 105.1577(1), γ= 91.2530(2)° and Z= 1 (trinuclear unit). The least-squares refinement bassed on 3091 significant reflections converged to R= 0.0362 and R′= 0.0424. A linear array of three copper(II) ions, with two crystallographically independent copper(II) atoms is the basis for this structure. The copper(II) ions are bridged by two H₂ahmt ligands co-ordinating via N¹ and N² and an asymmetric chloride bridge [Cu(1)–Cl(1) 2.296(1), Cu(2)–Cl(1) 2.688(1), Cu(1)–Cu(2) 91.09(4)°]. The Cu(1)⋯ Cu(2) distance is 3.5682(5)Å. The co-ordination geometry around the terminal copper(II) ions is completed by a non-bridging monodentate H₂ahmt ligand co-ordinating via N¹, a chloride atom and a hydroxyl group from one of the two bridging H₂ahmt ligands. Magnetic susceptibility measurements (6.5–295 K) are in accord with the trinuclear nature of this compound and could be fitted for an antiferromagnetic interaction (g= 2.00 and J=–16.9 cm^–1) between nearest neighbour copper(II) ions. The X- and Q-band powder EPR spectra are typical for a spin doublet. The presence of two different copper(II) chromophores is evident from the broad asymmetric band in the ligand field spectrum.