Tetra-n-butylammonium orotate monohydrate: knowledge-based comparison of the results of accurate and lower-resolution analyses and a non-routine disorder refinement

Abstract

The title hydrated molecular salt (systematic name: tetra-n-butylammonium 2,6-dioxo-1,2,3,6-tetrahydropyrimidine-4-carboxylate monohydrate), C16H36N+·C5H3N2O4−·H2O, crystallizes with N—H...O and O—H...O hydrogen-bonded double-stranded antiparallel ribbons consisting of the hydrophilic orotate monoanions and water molecules, separated by the bulky hydrophobic cations. The hydrophobic and hydrophilic regions of the structure are joined by weaker non-classical C—H...O hydrogen bonds. An accurate structure analysis conducted at T = 100 K is compared to a lower-resolution less accurate determination using data measured at T = 295 K. The results of both analyses are evaluated using a knowledge-based approach, and it is found that the less accurate room-temperature structure analysis provides geometric data that are similar to those derived from the accurate low-temperature analysis, with both sets of results consistent with previously analyzed structures. A minor disorder of one methyl group in the cation at low temperature was found to be slightly more complex at room temperature; while still involving a minor fraction of the structure, the disorder at room temperature was found to require a non-routine treatment, which is described in detail.

Keywords

• crystal structure
• orotate
• hydrophobic–hydrophilic molecular ion pair
• hirshfeld surface analysis
• knowledge-based analysis
• mogul geometry check