Inorganic compounds containing mixed anions display rich crystal chemistry and can exhibit interesting optical and magnetic properties. The combination of two anionic groups with different polarizabilities, point group symmetries, and valence states in a single material enables tunability of dimensionality and exchange interactions, leading to novel physical phenomena. In addition, the assembly of asymmetric anions with stereo-active lone pair electrons such as (SeO₃)^2- and tetrahedral anion groups such as (SO₄)^2- provides a route to noncentrosymmetric structures. Conventional synthesis of mixed anion systems usually involves mixing different reactive oxides and annealing them at high temperatures or in harsh solvent systems like HF. This approach often yields different product mixtures and impurities, preventing accurate characterization of structure and physical properties. To address this, we established new chemistry for designing mixed anion compounds, using organic molecules containing heavy main-group atoms. We developed a novel thiophene acylselenourea molecule - C₁₂H₁₀N₂OSSe as a precursor for the synthesis of new lanthanide selenite-sulfate systems - Ln₂(SeO₃)₂(SO₄)(H₂O)₂ (Ln = Sm, Dy, Yb), and characterized their crystal structure and magnetic properties by performing single crystal and powder X-ray diffraction, magnetization, and heat capacity measurements. Ln₂(SeO₃)₂(SO₄)(H₂O)₂ crystallizes in a polar chiral monoclinic lattice with space group C2. Their crystal structures feature a 3-dimensional anion network of (SeO₃)^2- trigonal pyramids and tetrahedral (SO₄)^2-. The magnetic properties of Ln₂(SeO₃)₂(SO₄)(H₂O)₂ indicate strong antiferromagnetic exchange interaction facilitated by strong spin-orbit coupling of the Ln³⁺ cations. Our results demonstrate a connection between organic and inorganic solid-state chemistry and create a new chemical pathway for making novel compounds with diverse structural architectures.

Thao Tran

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