Self-assembly of polymer and sheet structures in palladium(II) complexes containing carboxylic acid substituents

A series of complexes trans-[PdCl2L2] has been prepared by the reaction of [PdCl2(PhCN)(2)] and/or Na-2[PdCl4] with L = pyridine or quinoline ligands having one or two carboxylic acid groups. These complexes can form 1-D polymers through O-(HO)-O-... hydrogen bonding between the carboxylic acid groups, as demonstrated by structure determinations of [PdCl2(NC5H4-4-COOH)(2)], [PdCl2(NC5H4-3-COOH)(2)], and [PdCl2(2-Ph-NC9H5-4-COOH)(2)]. In some cases, solvation breaks down the O-(HO)-O-... hydrogen-bonded structures, as in the structures of [PdCl2(NC5H4-3-COOH)(2)](.)2DMSO and [PdCl2(2-Ph-NC9H5-4-COOH)(2)](.)4DMF, while pyridine-2-carboxylic acid underwent deprotonation to give the chelate complex [Pd(NC5H4-2-C(O)O)(2)]. The complexes trans-[PdCl(2)L2], L = pyridine-3,5-dicarboxylic acid or 2,6-dimethyl pyridine-3,5-dicarboxylic acid, self-assembled to give 2-D sheet structures, with hydrogen bonding between the carboxylic acid groups mediated by solvate methanol or water molecules. In the cationic complexes [PdL'L-2(2)](2+) (L'(2) = Ph2PCH2PPh2, Ph2P(CH2)(3)PPh2; L = pyridine carboxylic acid; anions X- = CF3SO3-), hydrogen bonding between the carboxylic acid groups and anions or solvate acetone molecules occurred, and only in one case was a polymeric complex formed by self-assembly.