Synthesis, characterization, crystal structures and magnetic properties of di- and polynuclear bis(μ-3-pyridin-2-yl-1,2,4- triazolato)copper(II) compounds containing N-methylimidazole, pyrazole or 4,4′-bipyridine as co-ligands

Abstract

A group of new compounds 1–5 of general formula [Cu 2(pt) 2L 2(NO 3) 2(H 2O) 2](H 2O) n , with n=1, 2, 3 or 4 and L= N-methylimidazole, pyrazole, 1 2 4,4′-bipyridine, H 2O and N-butylimidazole, has been prepared and characterized spectroscopically and structurally. The synthesis, characterization, spectral and magnetic properties as well as crystal and molecular structures of [bis(μ-3-pyridin-2-yl-1,2,4-triazolato- N′, N1, N2)]-bis[(1-methylimidazole- N3)(nitrato)(aqua)copper(II)] tetrahydrate, ([Cu 2(pt) 2(Meim) 2(NO 3)2(H 2O) 2](H 2O 4) 4 ( 1), in which pt=3-pyridin-2-yl-1,2,4-triazolato and Meim= N-methylimidazole, [bis(μ-3-pyridin-2-yl-1,2,4-triazolato- N′, N1, N2)]-bis[(pyrazole- N1)(nitrato)(aqua)copper(II)], [Cu 2(pt) 2(Hpz) 2(NO 3) 2(H 2O) 2] ( 2) in which Hpz=pyrazole, and an unusual chain of dimers, catena-(μ-4,4′-bipyridine)[bis(μ-3-pyridin-2-yl-1,2,4-triazolato- N′ N1 N2)(nitrato)(aqua)copper(II))], [Cu 2(pt) 2(4,4′-bpy)(NO 3)(H 2O) 2](NO 3)(H 2O) 4 ( 3) in which 4,4′-bpy=4,4′-bipyridine, have been studied Crystal structure data are as follows. 1: Cu 2N 14C 22H 34O 12, T=293 K, triclinic, space group P 1 , with a=9.2685(6), b=9.6897(6), c=10.2313(4) Å, α=108.700(4), β=97.884(4), γ=95.396(5)°, Z=1 and V=852.75(8) Å 3. The least-squares refinement based on 2111 significant reflections ( I>2σ( I) converged to R=0.0411 and R w=0.0446. 2: Cu 2N 14C 20H 22O 8, T=298 K, monoclinic, space group P2 1/ c, with a=10.812(1), b=13.750(1), c=10.003(1) Å, β=113.94(1)°, Z=2 and V=1359.1(2) Å 3. The least-squares refinement based on 1863 significant reflections ( I>2.5σ( I)) converged to R=0.0522 and R w=0.0485. 3: Cu 2N 12C 24H 30O 12, T=295 K, monoclinic, space group P2 1/ c, with a=8.8802(11), b=12.9975(8), c=28.7208(19) Å, β=92.970(7)°, Z=4 and V=3310.5(5) Å 3. The least-squares refinement based on 5100 significant reflections ( I>2σ( I)) converged to R=0.056 and R w=0.051. The structures of 1, 2 and 3 consist of dinuclear units, in which the copper(II) ions are linked by two via N(1), N(2) bridging dehydronated Hpt ligands in the equatorial plane. CuN distances vary from 1.970(3) to 1.988(3) Å. All copper(II) ions are in a distorted octahedral environment, of which the equatorial plane around the copper atoms is formed by three donor atoms of the pt ligand and one donor atom of another ligand (Meim, Hpz or 4,4′-bpy). A water molecule and a monodentate nitrate anion occupy the axial positions. The CuCu distances within the dinuclear unit are: 1, 4.022(1); 2, 3.9741(12); 3, 4.0198(7) Å. The 4,4′-bpy ligand bridges the dinuclear units to form a ladder type chain, with a CuCu distance measured over the 4,4′-bpy ligand of 11.1220(5) Å. The magnetic susceptibility data are interpreted on the basis of the spin Hamiltonian Ĥ=−2 J[ Ŝ Cu1· Ŝ cu2] and yielded 1: J=−47 cm −1, g=2.14; 2: J=−49 cm −1, g=2.04; 3: J=−51 cm −1, g=2.14; 4: J=−51 cm −1, g=2.00; 5: J=−51 cm −1, g=2.07. No interdimer interaction was found for 3. The X-band powder EPR spectra recorded at various temperatures for all compounds are typical of a triplet state, with D values in the range 0.08–0.10 cm −1.