Synthesis, structure and magnetic properties of two new spin-chain compounds Ca2Ni(HSeO3)2(SeO3)2 and Na2Cu(SeO3)2·2H2O.

Two new selenite compounds Ca2Ni(HSeO3)2(SeO3)2 (CaNi) and Na2Cu(SeO3)2·2H2O (NaCu) were obtained by a hydrothermal method. Both compounds crystallize in the triclinic system of space group P1̄, featuring a selenite-bridged one-dimensional (1D) spin-chain structure running along the a-axis. Magnetic measurements indicate that CaNi undergoes a long-range antiferromagnetic order (LRO) at TN = ∼3.8 K, while NaCu does not exhibit a LRO down to 2 K but the onset of a short-range correlation at TM = ∼30 K. The intrachain exchange coupling J/kB = -2.59 K for CaNi and J/kB = -47.13 K for NaCu can be estimated by a fit using the 1D spin-chain model. The thermogravimetric analyses show that both compounds are stable below 130 °C. The UV-vis diffuse reflectance spectra indicate that the band gaps of CaNi and NaCu are 4.38 eV and 3.18 eV, respectively.