Hydrogen-bond directed structural selectivity in asymmetric heterocyclic cations

The notion that the best hydrogen-bond donor preferentially interacts with the best hydrogen-bond acceptor has been explored in the synthesis and structural characterization of 12 salts based on asymmetric 2-aminopyrimidinium cations: 2-amino-4-methoxy-6-methylpyrimidinium 2-fluorobenzoate, 2-amino-4-methoxy-6-methylpyrimidinium 3-chlorobenzoate, 2-amino-4-methoxy-6-methylpyrimidinium 3-nitrobenzoate, 2-amino-4-methoxy-6-methylpyrimidinium benzoate, 2-amino-4-methoxy-6-methylpyrimidinium 3-N,N'(dimethyl)aminobenzoate, 2-amino-4-methoxy-6-methylpyrimidinium methylene-hydrogensuccinate hydrate, bis(2-amino-4-methylpyrimidinium) fumarate, 2-amino-4-methylpyrimidinium 3-fluorobenzoate, 2-amino-4-methylpyrimidinium nitrate, 2-amino-4-methylpyrimidinium 3-chlorobenzoate, 2-amino-4-methylpyrimidinium 2-methyl-hydrogenmaleate, and 2-amino-4-chloro-6-methylpyrimidinium 3,5-dinitrobenzoate toluene(0.4). In each structure, the -COO- acceptor consistently seeks out the -N-H+ donor generating the most important intermolecular interaction throughout this family of compounds. This exclusive recognition process can tolerate the presence of several other hydrogen-bond donors, which makes it a reliable structure-directing tool.