Cyanuric acid-melamine barbiturate

The self-assembly behaviour and complexing properties of several strapped porphyrin-incorporated melamine-cyanuric or melamine-barbiturate-based rosette supramolecules in chloroform-d has produced some intriguing structures. The almost perfect H-bonding complementarity of the constituent units, amphfied by their multiphcity, results in particularly stable structures whose integrity is maintained in solution [42]. Strapped porphyrin cyanuric acid 40a and its Zn (II) complex 40b were designed to combine with melamine derivatives 41 to afford stable porphyrin rosettes 42. The new porphyrin rosettes 42 could efficiently complex tripyridyl derivative 43 through intermolecular, cooperative coordination between Zn (II) and pyridine to form the stable rosette 44. 

Figures 5.2 and 6.2), the complex involving hydrogen-bonded barbiturate that should serve as sensor (Figure 6.9) and 234 have been presented earlier. The Whitesides rosette 3a [ 1 ], tapes 3b [2] and 109, crinkled tape 3c [ 1 ] (Figure 1.1) formed by melamine 1 and cyanuric acid 2 also shown earlier as well as... 

The complex between melamine and cyanuric acid (1 1) was reported in the literature in the late 1970s, but it was only in the early 1990s that the contributions from Whitesides and the concept of self-assembly popularized these systems [45]. Whitesides and co-workers reported the formation of tapes (Fig. 11.11), crinkled tapes and cyclic hexamers (rosettes) formed between barbituric acid and N,N -bis(p-substituted phenyl)melamine [46], In this they effectively blocked one face of melamine and, by manipulating substituents at the para position, different structures were obtained. Whiteside s putative suggestion that melamine/cyanuric acid formed an extended array (Fig. 11.12) was confirmed recently by Rao et al. with the crystal structure [47]. Hamilton and coworkers reported the crystal structure of a 5-substituted isophthalic acid derivative, which forms a cyclic aggregate held together with six pairs of hydrogen bonds, which in a way resembles the trimesic acid (Fig. 11.13) [48]. 

A classical two-component hydrogen-bonded system in self-assembly is represented by the melamine-barbituric/cyanuric acid complex. Whitesides and Lehn have exploited the complementarity of this interaction in the preferential formation of cyclic aggregates over the corresponding linear forms [69-71]. Cocrystals of 36 with 37, 38 and 39 indicate that the size of the substituent on the melamine component is essential in controlling the final supramolecular architecture (see Fig. 21). When relatively small substituents are present on the melamine subunit, one-dimensional tapes are formed. However, bulkier substituents enhance the formation of cyclic aggregates. 

Examples of cocrystals containing chains, ribbons, and other infinite ID motifs (Scheme 8) include bipyridine dihydroxybenzene, melamine cyanuric acid, bipyridine (fluorinated)dibromobenzene, 2-aminopyridine dicar-boxylic acids, triaminopyrimidine barbituric acid, 2-aminopyrimidine dicarboxylic acid, " 1,2,3-trihydroxy-benzeneihexamethylenetetramine, diols diamines, bis-benzimidazole dicarboxylic acids, and 2-amino-5-nitro-pyrimidine 2-amino-3-nitropyridine." ... 

Figure 3.20 Continued) (c) Formation of toroidal aggregates via assembly of barbituric acid/2,4,6-triamino-1,3,5-triazine building blocks. (Reproduced with permission from S. Yagai, S. Mahesh, Y. Kikkawa et aL, Toroidal nanoobjects from rosette assemblies of melamine-linked oligo(p-phenyleneethynylene)s and cyanurates., Angewandte Chemie International Edition, 2008, 47, 4691-4694. Wiley-VCH Verlag GmbH Co. KGaA.)...

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