Structure and Thermal Decomposition of Nd(III), Gd(III) and Tb(III) 2-Thiobarbiturates

Complexes [Ln₂(H₂O)₆(μ₂-Htba−O,O')₄(Htba−O)₂]_n (Ln = Tb (I), Gd (II), Nd (III); and H₂tba is thiobarbituric acid) have been synthesized. According to single-crystal X-ray diffraction, monoclinic crystals of I–III are isostructural. They contain three independent Htba^– ions (one terminal and two bridging) and two independent Ln³⁺ ions. Six Htba^– ligands (two terminal and four O,O'-bridging) and two water molecules are coordinated to one Ln³⁺ ion, and four O,O'-bridging Htba^– ions and four water molecules are coordinated to the other Ln³⁺ ion to form square antiprisms. The antiprisms are bound by Htba^– bridging ions into layers. Numerous hydrogen bonds and π–π interactions stabilize the structures of the compounds. Thermal decomposition of complexes I and II performed in air results in mixtures of oxides and oxysulfates, whereas complex III forms Nd₂O₂SO₄.