par Jones, Andrew 
;Wilson, Chick C.C.;Thomas, Lynne L.H.;Leech, Charlotte C.K.;McIntyre, Garry G.J.
Référence CrystEngComm, 16, 35, page (8177-8184)
Publication Publié, 2014-09
;Wilson, Chick C.C.;Thomas, Lynne L.H.;Leech, Charlotte C.K.;McIntyre, Garry G.J.Référence CrystEngComm, 16, 35, page (8177-8184)
Publication Publié, 2014-09
Article révisé par les pairs
| Résumé : | 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. This journal is © the Partner Organisations 2014. |
