Bridging behaviour of the 2-thio­barbiturate anion in its complexes with Li^I and Na^I

The structures of the Li^I and Na^I salts of 2-thio­barbituric acid (2-sulfanyl­idene-1-3-diazinane-4,6-dione, H₂TBA) have been studied. μ-Aqua-octa­aqua­bis­(μ-2-thio­barbiturato-κ²O:O′)bis(2-thio­barbiturato-κO)tetra­lithium(I) dihydrate, [Li₄(C₄H₃N₂O₂S)₄(H₂O)₉]·2H₂O, (I), crystallizes with four symmetry-independent four-coordinated Li^I cations and four independent HTBA⁻ anions. The structure contains two structurally non-equivalent Li^I cations and two non-equivalent HTBA⁻ anions (bridging and terminal). Eight of the coordinated water ligands are terminal and the ninth acts as a bridge between Li^I cations. Discrete [Li₄(HTBA)₄(H₂O)₉]·2H₂O complexes form two-dimensional layers. Neighbouring layers are connected via hydrogen-bonding inter­actions, resulting in a three-dimensional network. Poly[μ₂-aqua-tetraaqua­(μ₄-2-thio­bar­biturato-κ⁴O:O:S:S)(μ₂-thio­barbiturato-κ²O:S)disodium(I)], [Na₂(C₄H₃N₂O₂S)₂(H₂O)₅]_n, (II), crystallizes with six-coordinated Na^I cations. The octa­hedra are pairwise connected through edge-sharing by a water O atom and an O atom from the μ₄-HTBA⁻ ligand, and these pairs are further top-shared by the S atoms to form continuous chains along the a direction. Two independent HTBA⁻ ligands integrate the chains to give a three-dimensional network.