Issue 35, 2014

Engineering short, strong hydrogen bonds in urea di-carboxylic acid complexes

Abstract

A series of seven 2 : 1 molecular complexes of urea (U) and methyl ureas with di-carboxylic acids (A) are reported, along with the results of their study by variable temperature diffraction. These all contain short, strong O–H⋯O hydrogen bonds and a recurring acid⋯amide heterodimer forming U–A–U synthons. Despite differences in the degree of saturation of the linking C–C groups of the di-carboxylic acids and the single or double methyl substitution of one of the N atoms of the urea, the packing arrangements are remarkably similar in five of the complexes; the exceptions being N-methylurea oxalic acid and N,N-dimethylurea fumaric acid. The five similar molecular complexes all show contraction of one unit cell parameter on increasing temperature due to rearrangements of the weaker interactions which hold together the U–A–U units. The strength of the short, strong O–H⋯O hydrogen bond is shown to be linked both to the length of the connecting bridge between the carboxylic acid groups of the acid, and to the ΔpKa values between the two components.

Graphical abstract: Engineering short, strong hydrogen bonds in urea di-carboxylic acid complexes

Supplementary files

Article information

Article type
Paper
Submitted
21 mar. 2014
Accepted
17 abr. 2014
First published
17 abr. 2014

CrystEngComm, 2014,16, 8177-8184

Author version available

Engineering short, strong hydrogen bonds in urea di-carboxylic acid complexes

A. O. F. Jones, C. K. Leech, G. J. McIntyre, C. C. Wilson and L. H. Thomas, CrystEngComm, 2014, 16, 8177 DOI: 10.1039/C4CE00587B

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