Structural and Magnetic Properties of Two-Dimensional Oxalate-Bridged Bimetallic Compounds

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Abstract
Single crystals of (cat)±[MnIIMIII(C2O4)3] ferromagnetic (MIII˭CrIII, (cat)± = (n-Pr)4, n-Bu(Ph)3P), and antiferromagnetic (MIII˭FeIII, (cat)±=(n-Bu)4N, (Ph)4P) compounds have been synthesized in order to further elucidate the correlations between their structural and magnetic properties. Single crystal X-ray structural as well as 57Fe Mössbauer studies are reported here. In all these compounds, assigned to a space group R3c. Z=6. alternating [MnIIMIII(C2O4)3]nn-2D honeycomb-like networks, comprise [MIII(C2O4)3]3− building units of both kinds of chirality. It has been established that previously reported crystal data for ((n-Bu)4N)[MnIIFeIII(C2O4) 3] (space group P63, Z=2)[1] represent a polymorph structure with similar metallo-oxalate layers containing [FeIII(C2O4)3]3− units of the same kind of chirality (Δ or Δ). An account for twinning effects in crystallization allow us to locate carbon atoms of the (cat)± in unit cell. Zero- and high-field 57Fe Mössbauer spectroscopy of the polycrystalline compounds as a function of temperature revealed that: (i) ((n-Pn)4N)[MnIIeIII(C2O4)3] is a weak ferromagnet rather than a ferrimagnet, (ii) most of the {MnIIFeIII} and {FeIIFeIII} compositions are planar (XY) magnets exhibiting unusual magnetic relaxation well below Tc , and (iii) the negative magnetization previously observed[2] in ((n-Pn)4N)[FeIIFeIII(C2O4)3] is certainly a result of strong magnetic anisotropy and an occurrence of a “magnetic compensation point”, i.e. a crossing in FeII and FeIII sub-lattice magnetization curves.