Hydrothermal synthesis, structure, stability and magnetism of Na2Co2(C2O4)3(H2O)2:: a new metal oxalate ladder

Purple crystals of the compound Na2Co2(C2O4)(3)(H2O)(2) 1 were synthesized in high yielding hydrothermal reactions. The room temperature crystal structure reveals an anionic cobalt oxalate network with a 2-leg ladder topology. The ladder frameworks run parallel to the a axis and are held together by both hydrogen bonding and electrostatic interactions. The magnetism of 1 was studied as a function of temperature and field. The susceptibility shows a broad maximum at about 21 K which is associated with short-range correlations, and a phase transition to a long range ordered Neel state at about 9 K. Above T-N the data are fitted by a range of models which suggests the intra-ladder couplings are of the order -4 to -5 cm(-1) and the inter-ladder coupling is approximately 0.2 cm(-1). Themogravimetric analysis shows 1 to be stable up to 350 degrees C, where water of crystallisation is lost. A second decomposition episode is seen at 400 degrees C.