Synthesis, spectroscopic and magnetic properties of some pyrazine-bridged iron(II) sulfonate complexes

Abstract

Six new pyrazine-bridged complexes of iron(II) have been prepared and studied using magnetic susceptibility, differential scanning calorimetry, and vibrational, electronic, and Mössbauer spectroscopic methods. Fe(pyz)(CF3SO3)2 exhibits a susceptibility maximum at 4.4 K and analysis of the magnetic data according to a two-dimensional S = 2 system in the (isotropic) Heisenberg limit yields best-fit values of J = −0.26 cm−1 and g = 2.20. Variable temperature Mössbauer spectra between 4.2 and 1.6 K are also reported for this compound and show the onset of magnetic hyperfine splitting below ~3.8 K. Analysis of magnetic data for Fe(pyz)2(CH3SO3)2 and Fe(pyz)2(CF3SO3)2•CH3OH according to the two-dimensional Heisenberg model also indicates the presence of weak antiferromagnetic exchange in these complexes (J = −0.18 and −0.20 cm−1, respectively). No clear evidence for magnetic concentration was obtained from our studies on Fe(pyz)2(CIO4)2, Fe(pyz)(p-CH3C6H4SO3)2, and Fe(pyz)(p-CH3C6H4SO3)2•2CH3OH; any antiferromagnetic coupling in these complexes must be considerably weaker than in the other complexes studied.