Spectroscopic and magnetic identification of difluoro-bridged zigzag copper chains with substituted 5-phenylpyrazole ligands. Structural identification of catena-poly [bis(3-methyl-4-ethyl-5-phenylpyrazole)copper-di-μ-fluoro

Abstract

The synthesis, spectroscopic and magnetic properties of compounds from CuF 2·2H 2O and substituted 5-phenylpyrazoles are reported. The ligands used are 5-phenylpyrazole (abbreviated ppzH), 3,4-dimethyl-5-phenylpyrazole (dmppzH) and 3-methyl-4-ethyl-5-phenylpyrazole (meppzH). The crystal structure of [CuF 2(meppzH) 2] ∞ has been determined. The compound crystallized in the space group P 1 ; triclinic; a=13.888(6), b=5.671(3), c=15.181(6) Å, α= 91.95(4)°, β=111.56(3)°, γ=92.39(4)°, Z=2, R( R w)=0.0420(0.0581), with CuCu′=3.3295(7) and CuCu″=3.2935(7) Å. The monomeric unit consists of a chromophore CuN 2F 2 in a tetrahedrally distorted square plane with cis coordinated substituted N-donor pyrazoles at a distance of 1.992(2) and 1.996(2) Å and cis coordinated fluoride anions at a distance of 1.916(2) and 1.915(2) Å. Axial ligands are two fluoride anions of the nearby copper atoms of the next units along the chain, coordinated at distances of 2.448(2) and 2.400(2) Å, respectively. The so-formed zigzag chain consists of two different CuF 2Cu units positioned along the b axis. [p ]The structure is related to the spectroscopic and magnetic properties of the compounds. The infrared spectra show a strongly shifted NH stretching vibration around 2800 cm −1 and CuF vibrations near 400 and 450 cm −1 The EPR spectra at room temperature show an isotropic signal at g=2.13 for dmppzH and meppzH and an anisotropic signal with g⊥=2.09 and g‖=2.31 for ppzH. No hyperfine splitting is observed. At 77 K a weak half-field signal appears with g=4.11. [p ]Magnetic measurements in the region 4–300 K indicate a predominant paramagnetic character for all compounds. However, at very low temperatures (anti)ferromagnetism becomes apparent. The data, fitted on an isotropic linear chain with S= 1 2 and H =−2 J ϵ S i · S j , gave the best-fit parameters J=0.3 cm −1 and g=2.23 for CuF 2(meppzH) 2, J=1.4 cm −1 and g=2.22 for CuF 2(ppzH) 2 and J=−0.1 cm −1 and g=2.16 for CuF 2(dmppzH) 2.