Analogous Chain Selenite Chlorides Ba₂M(SeO₃)₂Cl₂ (M = Cu²⁺, Ni²⁺, Co²⁺, Mn²⁺) and Pb₂Cu(SeO₃)₂Cl₂ with Tunable Spin S: Syntheses and Characterizations

A series of analogous chain selenite chlorides Ba₂M(SeO₃)₂Cl₂ (M = Cu 1, Ni 2, Co 3, Mn 4) and Pb₂Cu(SeO₃)₂Cl₂ 5 with tunable spin S from S = 1/2 to S = 5/2 have been hydrothermally synthesized and characterized. These analogues crystallized in the orthorhombic Pnnm space group (monoclinic P2₁/n space group for 5) all containing M²⁺-SeO₃-M²⁺ spin chains, which are further separated by the Ba²⁺ ions (Pb²⁺ for 5). The magnetic susceptibility results of 1, 2, and 5 show broad maxima around 80.0, 18.9, and 78.0 K, respectively, indicating good one-dimensional (1D) magnetism. Meanwhile, no long-range order (LRO) is observed down to 2 K for both 1 and 5, while the isostructural compounds 2, 3, and 4 exhibit LRO at 3.4 K, 10.8 K, and 5.7 K, respectively, which are further confirmed by the heat capacity and electron spin resonance results, as well as the observed spin-flop transitions in the M-H curves measured at 2 K below T_N. The magnetizations of 1-5 at 7 T are still far from saturation. In addition, thermal stability and FT-IR and UV-vis-NIR spectroscopy of 1-5 are reported.