Classical hydrogen bonding and weaker C–H⋯O interactions in complexes of uracil-5-carboxylic acid with the alkali metals Na–Cs

Reaction of uracil-5-carboxylic acid with M2CO3 or M(OH) (M = Na–Cs) gave five new polymeric coordination compounds: [Na(C5H3N2O4)(H2O)]∞ (1); [K(C5H3N2O4)(C5H4N2O4)]∞ (2); [Rb{H(C5H3N2O4)2} · 2H2O]∞ (3); [Rb(C5H3N2O4)(H2O)]∞ (4); [Cs{H(C5H3N2O4)2}(H2O)2]∞ (5). Characterisation by single-crystal X-ray diffraction using both standard laboratory equipment and high-flux synchrotron radiation revealed that very different hydrogen bonding networks are formed in each case. Hydrogen-bonded chains (1), sheets (2 and 5) and tapes (3 and 4) are all found in these compounds. All except 3 additionally contain C–H⋯O interactions as an integral part of the hydrogen bonding motifs formed. Compounds 3 and 5 also feature centrosymmetric hydrogen bonds as a result of partial deprotonation, whereby a single hydrogen atom is shared equally between two carboxylate groups.

Five alkali metal complexes of the organic acid uracil-5-carboxylic acid, all synthesised from aqueous solution, are presented. Crystal structure analysis showed that hydrogen bonding is important in all compounds, with chain, sheet and tape motifs being formed. C–H⋯O hydrogen bonding, although weaker, also has a major role to play in most of the structures.Figure optionsDownload as PowerPoint slide