N–H…N(pyridyl) and N–H…O(urea) hydrogen bonding and molecular conformation of N-aryl-N′-pyridylureas
作者:Sreekanth K. Chandran、Naba K. Nath、Suryanarayan Cherukuvada、Ashwini Nangia
DOI:10.1016/j.molstruc.2010.01.030
日期:2010.4
Analysis of N-Ar-N'-4-pyridylureas (Ar = 4-X-phenyl, 4-py) crystal structures shows a gradual transition from urea...pyridyl N-H center dot center dot center dot N hydrogen bond in bifurcated synthon of R-2(1) (6) graph set (X = H, Me, Cl) to single N-H center dot center dot center dot O and N-H center dot center dot center dot N hydrogen bonds in X = Br, I to urea N-H center dot center dot center dot N tape synthon (R; (6) graph set) in N-phenyl-M-tetrafluoropyridylurea. Thus the two extremes of urea pyridyl N-H center dot center dot center dot N synthon in N,N'-di(4-pyridyl) urea, N-H center dot center dot center dot N tape characteristic of diphenyl urea together with an in-between state are now visualized as snap shots in the solid-state. Most remarkably, molecular conformations too show a transition: the diaryl urea molecule is in the twisted metastable conformation in N-H center dot center dot center dot N tape structures, it is coplanar in the flat stable conformation for N-H center dot center dot center dot N structures, and one NH is in-plane while the other is oriented slightly outwards in the intermediate N-H center dot center dot center dot N and N-H center dot center dot center dot N hydrogen-bonded structure of N-4-Br-phenyl-N'-4-pyridylurea. Subtle and yet observable one-to-one molecular conformation to crystal structure systematic effects are analyzed. A one-dimensional zigzag chain in the crystal structure of N,N'-di(4-pyridyl) urea is consistent with the hydrogen bonding model for organic gelators. (C) 2010 Elsevier B.V. All rights reserved.