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

The structures of the LiI and NaI 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 LiI cations and four independent HTBA− anions. The structure contains two structurally non-equivalent LiI 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 LiI 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 NaI 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.