Crystal structures of cesium and rubidium 2-thiobarbiturates

The crystal structures of cesium 2-thiobarbiturate C₄H₃CsN₂O₂S (I) and rubidium 2-thiobarbiturate C₄H₃N₂O₂RbS (II) (C₄H₄N₂O₂S is 2-thiobarbituric acid, H₂TBA) have been determined. Isostructural crystals are monoclinic; a = 7.9609(3) Å,b = 11.8474(3) Å, c = 7.7317(2) Å, β = 101.285(3)°, V = 715.13(4) ų, space group C2/m, Z = 4 for I and a = 7.6369(2) Å, b = 11.7690(3) Å, c = 7.5568(2) Å, β = 100.212(1)°, V = 668.44(3) ų, space group C2/m, Z = 4 for II. Each metal ion in complexes I and II is bonded to four oxygen atoms and two sulfur atoms at the vertices of a six-vertex polyhedron. N-H…O hydrogen bonds link HTBA-ions into chains. The structure is also stabilized by the “head-to-tail” π-π interaction of HTBA-ions.