Engineering short, strong hydrogen bonds in urea di-carboxylic acid complexes
Engineering short, strong hydrogen bonds in urea di-carboxylic acid complexes
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DOI：
10.1039/c4ce00587b
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发表时间：
2014-08
期刊：
影响因子：
3.1
通讯作者：
Andrew O. F. Jones;Charlotte K. Leech;G. McIntyre;Chick C. Wilson;L. Thomas
中科院分区：
文献类型：
--
作者：
Andrew O. F. Jones;Charlotte K. Leech;G. McIntyre;Chick C. Wilson;L. Thomas
一系列的七个2：本文报道了脲（U）和甲基脲（A）与二元羧酸（A）的分子配合物，并沿着了用变温衍射法研究它们的结果。它们都含有短的、强的O-H-O氢键和形成U-A-U双离子的重复性酸N-异二聚体。尽管二羧酸的连接C-C基团的饱和度和尿素的N原子之一的单或双甲基取代存在差异，但在五种络合物中，堆积排列非常相似;例外是N-甲基脲草酸和N，N-二甲基脲富马酸。五个相似的分子复合物都表现出一个单位晶胞参数的收缩，由于较弱的相互作用，保持在一起的U-A-U单元的重排增加温度。短而强的O-H-O氢键的强度被证明与酸的羧酸基团之间的连接桥的长度以及两个组分之间的ΔpKa值有关。
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.