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.