Structural and magnetic properties of two-dimensional oxalate-bridged bimetallic compounds

Single crystals of (cat)(+)[(MnMIII)-M-II(C2O4)(3)] ferromagnetic (M-III=Cr -III, (cat)(+)=(n-Pr)(4), n-Bu(Ph)(3)P), and antiferromagnetic (M-III=Fe-II I, (cat)(+)= (n-Bu)(4)N, (Ph)(4)P) compounds have been synthesized in order to further elucidate the correlations between their structural and magneti c properties. Single crystal X-ray structural as well as Fe-57 Mossbauer st udies are reported here. In all these compounds, assigned to a space group R3c, Z=6, alternating [(MnMIII)-M-II(C2O4)(3)](n)(n) - 2D honeycomb-like ne tworks, comprise [M-III(C2O4)(3)](3-) building units of both kinds of chira lity. It has been established that previously reported crystal data for ((n -Bu)(4)N)[(MnFeIII)-Fe-II(C2O4)(3)] (Space group P6(3), Z=2)([1]) represent a polymorph structure with similar metallo-oxalate layers containing [Fem( C2O4)(3)](3-) units of the same kind of chirality (Lambda or Delta). An acc ount for twinning effects in crystallization allow us to locate carbon atom s of the (cat)(+) in unit cell. Zero- and high-field 57Fe Mossbauer spectro scopy of the polycrystalline compounds as a function of temperature reveale d that: (i) ((n-Pn)(4)N)[Mn(II)e(III) (C2O4)(3)] is a weak ferromagnet rath er than a ferrimagnet, (ii) most of the {(MnFeIII)-Fe-II} and {(FeFeIII)-Fe -II} compositions are planar (XY) magnets exhibiting unusual magnetic relax ation well below T-c, and (iii) the negative magnetization previously obser ved([2]) in ((n-Pn)(4)N)[(FeFeIII)-Fe-II(C2O4)(3)] is certainly a result of strong magnetic anisotropy and an occurrence of a "magnetic compensation p oint", i.e. a crossing in Fe-II and Fe-III sub-lattice magnetization curves .