Five pseudopolymorphs of 6-amino-2-thio­uracil: absence of N—H...S hydrogen bonds

In order to study the preferred hydrogen-bonding pattern of 6-amino-2-thio­uracil, C₄H₅N₃OS, (I), crystallization experiments yielded five different pseudopolymorphs of (I), namely the dimethyl­formamide disolvate, C₄H₅N₃OS·2C₃H₇NO, (Ia), the dimethyl­acetamide monosolvate, C₄H₅N₃OS·C₄H₉NO, (Ib), the dimethyl­acetamide sesquisolvate, C₄H₅N₃OS·1.5C₄H₉NO, (Ic), and two different 1-methyl­pyrrolidin-2-one sesquisolvates, C₄H₅N₃OS·1.5C₅H₉NO, (Id) and (Ie). All structures contain R₂¹(6) N—H...O hydrogen-bond motifs. In the latter four structures, additional R₂²(8) N—H...O hydrogen-bond motifs are present stabilizing homodimers of (I). No type of hydrogen bond other than N—H...O is observed. According to a search of the Cambridge Structural Database, most 2-thio­uracil derivatives form homodimers stabilized by an R₂²(8) hydrogen-bonding pattern, with (i) only N—H...O, (ii) only N—H...S or (iii) alternating pairs of N—H...O and N—H...S hydrogen bonds.

An approach to creating novel anions: silylated triel compounds with -CH₂- and -O- linkers, [InCl₂{O(HO)Si(t-Bu)₂}]₂ and Li[B(CH₂SiMe₃)₄]

Bis­[[mu]-di-tert-butyl­(hy­droxy)­silanol­ato]­bis­[chlorido­indium(III)], [In₂(C₈H₁₉O₂Si)₂Cl₄], (I), is a centrosymmetric two-centre indium complex featuring a system of three annulated four-membered rings; the structure is the first example of an In₂O₂ ring which is annulated with two Si-O units to form a ring system composed of three rings. The coordination environment of the In centres is a distorted trigonal bipyramid. The crystal packing of (I) is characterized by chains of mol­ecules connected by O-H...Cl hydrogen bonds. The crystal of (I) was a nonmerohedral twin. There is no known example of an In₂O₂ ring in which the In atoms carry any two halogen ligands. The structure of tetra­kis­(tetra­hydro­furan)­lithium tetra­kis­[(tri­methyl­silyl)­methyl]­borate, [Li(C₄H₈O)₄](C₁₆H₄₄BSi₄), (II), is composed of discrete cations and anions. The coordination geometries of the Li and B centres is tetra­hedral. The cations and anions lie in planes parallel to the ab plane. There are no short contacts between the cations and anions. Compound (II) is the first example of a B centre bonded to four -CH₂Si units.

Three new pseudopolymorphs of 6-amino­uracil

The structures of two 6-amino­uracil di­methyl­acetamide monosolvates and a 1-methyl­pyrrolidin-2-one monosolvate display N-H...O hydrogen-bonding patterns that link the uracil mol­ecules to their respective solvent mol­ecules. The formation of (8) N-H...O hydrogen-bond motifs between 6-amino­uracil mol­ecules can only be found in two-dimensional frameworks, whereas (14) N-H...O patterns are present when zigzag chains of 6-amino­uracil mol­ecules are formed.