EXCHANGE INTERACTIONS AND SPIN DYNAMICS IN A [CUND2(C4O4)(4)(H2O)(16)]CENTER-DOT-2H(2)O CRYSTAL

Crystalline [CuNd2(C4O4)(4)(H2O)(16)]. 2H(2)O constructed of complexes of trivalent neodymium and divalent copper, has been synthesized and studied by EPR. The square anion groups (C4O4) enter as bridge ligands , forming chains of neodymium ions interconnected by (C4O4)Cu(C4O4) fr agments. It is found that the relaxation rate of the neodymium subsyst em at room temperature significantly exceeds the exchange interaction rate between copper and neodymium ions. Under these conditions the mag netic properties of the crystal are determined by two magnetically non equivalent chains of copper ions, which do not interact. The intrachai n exchange interaction via hydrogen bonds is estimated to be similar t o 0.1 cm(-1). As one proceeds from the high-temperature 125Q<T<300 K) to the low-temperature region (T<40 K), a substantial change in the na ture of the interaction is revealed. An unusual magnetic structure giv en in a crystal is observed at bw temperatures, which is determined by the presence of two magnetically nonequivalent ''ribbons,'' formed by the interacting copper and neodymium ions: chains of copper ions are framed on two sides by chains of neodymium ions. The magnitude of the parameter of the exchange interaction between the copper and neodymium ions is estimated as J(Cu-Nd)greater than or equal to 0.2 cm(-1). An exchange interaction between magnetically nonequivalent neodymium ions is not revealed in the EPR spectra.