pKa‐Directed Host–Guest Assemblies: Rational Analysis of Molecular Adducts of 2,4‐Diamino‐6‐methyl‐1,3,5‐triazine with Various Aliphatic Dicarboxylic Acids

Molecular adducts of 2,4-diamino-6-methyl-1,3,5-triazine (1) have been prepared with various aliphatic dicarboxylic acids. The molecular complexes (1 a-1 i) thus formed by co-crystallizing 1 with oxalic, malonic, succinic, fumaric, acetylene dicarboxylic, glutaric, thiodiglycolic, diglycolic, and adipic acids have been found to give two types of host-guest assemblies that have voids or channels in a three-dimensional arrangement. The different types of host-guest arrangement appear to result from differences in the acidity of the dicarboxylic acids, that is, acids with pK(a)<3.0 give host networks that consist of 1 and the corresponding acid with water or solvent molecules of crystallization present as guests, whereas acids with pK(a)>3.0 exist as guests in voids in a host network formed by 1. The former arrangement is observed in adducts 1 a, 1 b, 1 e, and 1 h and the latter arrangement is found in adducts 1 c, 1 d, 1 f, 1 g, and 1 i.