Magnetic susceptibility data for several Fe(II) coordination polymers containing oxalate or squarate dianions are reported in the temperature range 4.2-300 K. Low-temperature magnetism of Fe(C2O4)(H2O)2 is dominated by intrachain ordering near 32 K followed by the onset of interchain long-range order slightly below this temperature. Susceptibility data for Fe(C4O4)(H2O)2 and Fe(C4O4)(C5H5N) 2·2H2O show no detectable spin exchange in the temperature range studied. Susceptibility data to 1.8 K for Fe(C4O4)(C4H4N 2)·41/2H2O are analyzed on the basis of a modified Heisenberg linear chain model with an intrachain exchange parameter of approximately -0.3 cm-1 and a negligible interchain exchange parameter. Mössbauer spectral data for these Fe(II) complexes are reported in the temperature range 17-300 K. The observed temperature dependence of the quadrupole splitting for Fe(C4O4)(H2O)2, Fe(C4O4)(C5H5N) 2·2H2O, and Fe(C4O1)(C4H4N 2)·41/2H2O is described in terms of an excited 5Eg term which lies 525, 425, and 850 cm-1, respectively, above the 5B2g ground term. Ground- and excited-term splittings are in essential agreement with those obtained from room-temperature solid-state electronic spectra of these materials. Controlled chemical oxidation of Fe(C2O4)(H2O)2 with Br2 or 1,4-benzoquinone in 1,2,4-trichlorobenzene yields discrete mixed-valence compounds Fe(C2O4)(H2O)1 4Br0 6 and Fe(C2O4)(H2O)0 9(C6H4O2)0 05. These semiconducting materials (σ300K ≃ 10-4 Ω-1 cm-1) display Mössbauer spectra in the range 20-400 K which are characteristic of Fe(II, III) mixed-valence polymers. Below approximately 20 K, spectra of these compounds consist of superimposed paramagnetic and Zeeman hyperfine multiplets. Fe(C4O4)(C5H5N)I1 5 and Fe(C6H2O4)I are obtained by solid-state I2 oxidation of Fe(C4O4)(C5H5N) 2·2H2O and Fe(C6H2O4)(H2O)2. respectively. Mössbauer spectral parameters for these iodine oxidation products are consistent with the presence of Fe(II) and Fe(III) sites in the approximate ratio of 3:1. Variable-temperature magnetic susceptibility data for the mixed-valence complexes indicate the presence of antiferromagnetic spin exchange which is described with appropriate theoretical expressions for the susceptibility. With the possible exception of Fe(C4O4)(C5H5N)I1 5, the mixed-valence compounds appear to be structurally described as randomly oxidized linear chain coordination polymers. Infrared spectral band assignments for the single- and mixed-valence complexes support the proposed structures for these materials. © 1979 American Chemical Society.
