Solids, supramolecular synthesis hydrogen bonding

In this extensive study of thiourea synthesis by coupling isothiocyanates with amines under mechanochemical conditions of neat and LAG, a total of 49 different thiourea derivatives were prepared. Since the supramolecular chemistry of simple synunetrical and nonsymmetrical diarylthiouieas had not previously been studied in detail, the information from the PXRD patterns of the milling products in this work also allowed for a systematic analysis of structural features of diarylthio-ureas. The three main self-assembly motifs were identified. A characteristic supramolecular synthon based on bifurcated N—H - S hydrogen bonds was found in most cases, whereby the individual thiourea molecules were assembled into chains aligned in a head-to-head (parallel molecular dipoles) or head-to-tail (antiparallel molecular dipoles) manner. In the case of slerically hindered thioureas, such as A -(2,6-dimethylphenyl)-A -phenylthiourea, the third motif arising from discrete cen-trosymmetric dimers based on rI(S) supramolecular synthon was found. A detailed look at the measured PXRD patterns for aU diarylthioureas revealed that solid-state structures of these compounds could be classified into two structural families, denoted as family I and family II (Fig. 1.11). 

Supramolecular interactions were also utilized in synthesis of carbon nanotube/poly-propylene composites (see chapter Applications of Ball Milling in Nanocarbon Material Synthesis). Solid-state grafting of maleated polypropylene on the surface of multiwalled carbon nanotubes (MWCNTs) employs interactions of carbonyl and carboxyl groups with maleic anhydride groups via hydrogen bonds or other dipole-dipole interactions [8]. 

In the quest for polymorphic modification of the adduct with pimelic acid, the only cocrystal containing an extended hydrogen bonded network and not a supramolecular macrocycle, vapor digestion of a mixture of solid [Fe( ] -C5H4-C5H4N)2] and solid pimelic acid HOOC(CH2)sCOOH in the presence of solvent vapors was attempted showing that the stoichiometry of the products was affected by the protic or aprotic nature of the solvent. The cocrystal with 1 1 stoichiometric ratio as observed in the grinding synthesis was obtained by exposure to... 

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