Study of the two-dimensional [MM′(C3H2O4)2(H2O)4] (M = Ba, Sr and M′ = Cu, Mn) systems:: Synthesis, structure, magnetic properties, and thermal decomposition

Compounds with the general formula [MM'(C3H2O4)(2)(H2O)(4)] (M = Ba, Sr; M' = Cu, Mn; C3H2O4 = malonate) have been synthesized and characterized. Single-crystal X-ray diffraction study on the [SrCu(C3H2O4)(2)(H2O)(4)] compound indicates that it crystallizes in the orthorhombic space group, Peen, Z = 4, with unit cell parameters a = 6.719(2), b = 18.513(7), and c = 9.266(4) Angstrom. The structure consists of distorted octahedral copper(II) species which are extended along the ac plane forming a two-dimensional structure; The geometry of the alkaline-earth;ions resembles a distorted antiprism. The other compounds are isostructural. The EPR spectra of the [MCu-(C3H2O4)(2)(H2O)(4)] (M = Ba, Sr) compounds show an orthorhombic g tensor as consequence of a linear combination of the axial symmetry and the exchange interactions between magnetically different centers, but crystallographically equivalent. For the manganese compounds, the EPR spectra of polycrystalline samples show that the intensity of the signal increases with decreasing temperature down to 20 K, and at lower temperatures the intensity decreases, becoming silent below 7 K. Magnetic measurements show two-dimensional (2D) ferromagnetic and antiferromagnetic interactions for the copper and manganese phases, respectively. in all cases, the susceptibility data were fitted by the expression for a Heisenberg square-planar system. The obtained J/k values are 1.44 and 1.15 K, for the SrCu and BaCu compounds, respectively, and -0.65 and -0.59 K for the SrMn and BaMn compounds, respectively. For the manganese compounds, magnetic measurements show a magnetic ordering below 5 K which confirms the presence of a weak ferromagnetism. Thermal analyses of the phases show three different decomposition steps: dehydration, ligand pyrolysis, and evolution of the inorganic residue for all compounds. Taking these results into account, we performed further thermal treatments to obtain mixed oxides. These were obtained at short reaction times and at temperatures lower than those of the conventional ceramic method.