Synthesis and thermal transformation of a neodymium(III) complex [Nd(HTBA)₂(C₂H₃O₂)(H₂O)₂]·2H₂O to non-centrosymmetric oxosulfate Nd₂O₂SO₄

<div><p>Neodymium complex [Nd(HTBA)₂(C₂H₃O₂)(H₂O)₂]_n·2nH₂O (<b>1</b>) (H₂TBA = 2-thiobarbituric acid, C₄H₄N₂O₂S) has been synthesized in an aqueous solution at 80–90 °C. The crystal structure of <b>1</b> has been determined by the Rietveld method in space group P2₁/n, <i>a</i> = 8.5939(2), <i>b</i> = 22.9953(5), <i>c</i> = 10.1832(2) Å, <i>β</i> = 112.838(1)°, <i>Z</i> = 4, and <i>R</i> = 0.0181. In <b>1,</b> the Nd(III) is coordinated by four μ₂-HTBA^– ions through O, three oxygens from two μ₂-η² : η¹-bridging CH₃COO^– anions, and two terminal waters with a tri-capped trigonal prism structure. The prisms form an edge-contact pair through two O from two acetates. The pairs are connected by HTBA^– and form a 3-D framework. The principle product of thermal decomposition of <b>1</b> at >750 °C is Nd₂O₂SO₄ (<b>2</b>). The crystal structure of <b>2</b> has been obtained in space group I222, <i>a</i> = 4.1199(4), <i>b</i> = 4.2233(4), <i>c</i> = 13.3490(12) Å, <i>Z</i> = 2, and <i>R</i> = 0.0246. The structure is related to an orthorhombic structure type of M₂O₂SO₄ (M = Ln) compounds. In <b>2</b>, the Nd³⁺ is coordinated by six oxygens in a trigonal prism. Each NdO₆ prism links with two SO₄ tetrahedra by nodes, with four other NdO₆ prisms by edges, and with four other NdO₆ prisms by nodes, and the units form the 3-D frame. In the frame, the layers of SO₄ tetrahedra are alternated by two NdO₆ prism layers.</p></div