Link between Isostructurality, Polymorphism, and Weak Interactions in Palladacycle Crystals: Chemical Insight

A series of organopalladium salts of the general formula, LPdX {L = phenyl azo-thioether based tridentate (C, N, S) ligand with different substituent and X = Cl, Br, I, NO3, ClO4}, have been synthesized with an objective to investigate the reliability of auxiliary C–H···X synthons in dictating the crystal packing of these molecules. The compounds were characterized both in solution and solid state by spectroscopic and X-ray diffraction methods. Crystal structures of these solids show that the presence of two phenyl rings with almost planar configuration enforces stacking between the molecules through π···π and C–H···π interactions. The nature of the stacking, however, varied depending on the relative strength of C–H···X interactions. Methyl substituted ligand resulted in isostructural solids for all halo salts. The unsubstituted and chloro substituted ligands yielded isostructures only for chloride and bromide salts. The chloride salt of chloro-substituted ligand led to a pair of concomitant polymorphs. The salts based on polyatomic anions, namely, nitrate and perchlorate resulted in different crystal packing because of dominant C–H···O interactions. The paper highlights the influence of auxiliary C–H···X interactions in dictating isostructures and polymorphs among a series of palladacycle crystals.