Self-assembly of supramolecular structures from palladium chloride and guanidinium salts of pyridinecarboxylic acids - A dramatic change on passing from the para- to the meta-substituted acid

Supramolecular structures 1 and 2 were obtained in the solid state from the reaction between palladium chloride and guanidinium salts of p- and m-pyridinecarboxylic acid, respectively. The pyridinecarboxylate anions were trans-coordinated to palladium dichloride through nitrogen, and the carboxylate groups formed hydrogen bonds with guanidinium cations. The present paper describes a remarkable change in the stoichiometry and structural organization of the solid 3 derived from the meta-substituted acid 2, triggered by the elimination of one guanidine molecule as hydrochloride per molecule of palladium chloride, during crystallization from methanol. The corresponding isonicotinate 1 structure appears to be stable under the same conditions. As shown by the analysis of the crystal structures, the guanidinium nicotinate organic salt 4 turns out to be preorganized to host palladium chloride both in 2 and 3. © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.