Synthesis, spectroscopic and magnetic properties of linear nickel(II) and cobalt(II) trimers containing substituted 1,2,4-triazoles and fluoride as bridging ligands. The X-ray structure of bis [(μ-fluoro)bis(μ-3, 4, 5-trimethyl-1,2, 4-triazole-N1,N2)bis-(thiocyanato-N)(aqua)cobalt(II)-F,N1,N1′,] cobalt(II) tetrahydrate

Abstract The preparation and properties of a new series of triazole- and fluoro-bridged trimeric compounds, containing Co(II) and Ni(II) as metal ions, are described. The compounds have the general formula M 3 L 4 F 2 (NCS) 4 (H 2 O) x , where L denotes 3,5- dimethyl-1,2,4-triazole (dmtrH, C 4 H 7 N 3 ), 4-amino- 3,5-dimethyl-1,2,4-triazole (admtr, C 4 H 8 N 4 ), 3,4,5- trimethyl-1,2,4-triazole (tmtr, C 5 H 9 N 3 ) and 4- amino-3,5-diethyl-1,2,4-triazole (adetr, C 6 H 12 N 4 ), respectively, and x = 2–6. Dark red crystals of [Co 3 (tmtr) 4 F 2 (NCS) 4 (H 2 O) 2 ](H 2 O) 4 are monoclinic, space group P 2 1 / n , with a = 9.834(2), b = 12.106(1), c = 18.657(2) A, β = 99.60(1) o , V = 2190 A 3 and Z = 2; the measured and calculated densities are 1.52(1) and 1.52 Mg m −3 , respectively. The X-ray analysis was done using counter data (3642 significant reflections). The structure was solved by the heavy atom method and refined by full-matrix least- squares methods to a final R of 0.034 ( R w = 0.045). Neighbouring Co(II) ions in the linear trimer are linked by two 1,2-bidentate triazole ligands and one fluoride anion. The coordination sphere of the terminal Co(II) ions is completed by two N-bonded thiocyanate anions and one water molecule. The distance in the trimer is 3.4015(3) A. The CoF distances are 2.023(1) and 2.058(2) A, whereas the CoN(triazole) distances are somewhat larger (2.13–2.17 A). The magnetic properties of the trimeric Ni compounds are satisfactorily described by the isotropic Heisenberg model, yielding characteristic exchange constants J in the range −11 – −15 cm −1 and g -factors in the range 2.20–2.27. An Ising type of Hamiltonian is used for the interpretation of the magnetic data of the cobalt trimers, assuming an effective spin of 1 2 for Co and neglecting λ⊥. The exchange constants J ‖ obtained range from −7 to −35 cm −1 with g ‖ values of 6.1–9.2. These values are rough estimates only, because the good agreement with theory only occurs at temperatures below 20 K. The magnetic properties of the compounds are compared to magnetic data of closely related compounds.