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)