Tetra- and decanuclear iron(II) complexes of thiacalixarene macrocycles:: Synthesis, structure, Mossbauer spectroscopy and magnetic properties

Two iron(II) complexes, namely [Fe-4(L)(2)]center dot H2O (1) and [Fe-10(L)(4)Cl-4]center dot 2H(2)O (2), have been synthesised under solvothermal conditions by treating p-tert-butylthiacalix[4]arene (LH4) with FeCl2 in methanol. Compound 1 crystallises in the orthorhombic system (space group 1mmm) with the unit-cell parameters a = 17.8308(4), b = 19.1372(3), c = 28,8391(6) angstrom and V = 9840.8(3) angstrom (Z = 2). Compound 2 crystallises in the triclinic system (space group P (1) over bar with the unit-cell parameters a = 13.8036(4), b = 18.8373(4), c = 20.1978(6) angstrom, a = 65.772(2)degrees, beta = 74.120(1)degrees, gamma = 71.922(1)degrees and V = 4487.6(2) angstrom(3) (Z = 1). Compound 1 is a neutral tetranuclear complex and is best described as an iron(II) square sandwiched between two thiacalixarene macrocycles. Each iron centre is six-coordinate in a trigonal-prismatic geometry made up of four phenoxy oxygen atoms plus two sulfur atoms. Compound 2 is a neutral centrosymmetric decanuclear complex and may be viewed as a dimer of double chloro-bridged pentanuclear complexes. Mossbauer spectra of compounds 1 and 2 have been recorded at different temperatures between 80 and 298 K. Each sub-spectrum can be characterised by a quadrupolar doublet corresponding to different iron environments where all iron ions are in high-spin state (S = 2). The hyperfine parameters (quadrupole splitting, isomer shift and line. width) as well as the Mossbauer spectra area-ratios are in good agreement with the crystallographic data. The two compounds exhibit magnetic behaviours indicating that antiferromagnetic interactions occur between the iron(II) centres. The simulation of the magnetic susceptibility was done in the case of compound I with a single exchange coupling constant J = -4 cm(-1) and g = 2.02) between the iron(II) ions [H = -J(S1S2 + S2S3 + S3S4 + S1S4)].