EFFECTS OF THE BASE AND SOLVENT ON THE FORMATION OF HETEROMETALLIC SODIUM-PALLADIUM(II) COORDINATION NETWORKS WITH 2-HALONICOTINATES

MARICEL RODRIGUEZ; FABIO DOCTOROVICH; BORIS-MARKO KUKOVEC

Mar del Plata

Congreso; XVIII Reunión Anual de la Asociación de Cristalografía Argentina; 2023

AACr

The effect of the base and solvent choice on the formation of 2D heterometallic sodium-palladium(II) coordination polymers with 2-halonicotinates (2-chloronicotinate (2-Clnic) and 2-bromonicotinate (2-Brnic)) was studied. These ligands are suitable for construction of coordination polymers due to their bridging potential. The choice of the halosubstituent type (chloride vs. bromide) in the same position (-2) on the halonicotinate pyridine ring and its influence on their dimensionality (1D vs. 2D polymers) and physical properties is also of interest [1]. The 2D coordination polymers, {[Na2(H2O)2(μ-H2O)4PdCl2(μ-2-Clnic-N:O')2]}n (1) and {[Na2(H2O)2(μ-H2O)4PdBr2(μ-2-Brnic-N:O')2]·2H2O}n (2), were formed in aqueous solution in the presence of NaHCO3, whilst the palladium(II) monomers with the same halonicotinates, [PdCl2(2-ClnicH-N)2]·2DMF (3) and [PdCl2(2-BrnicH-N)2]·2DMF (4), were obtained from DMF/water mixture. Since the carboxylic groups are deprotonated in the presence of base, the carboxylate O atoms are able to coordinate to sodium ions. Hence, the resulting 2D coordination networks of (1) and (2) are composed of the zigzag chains of water-bridged sodium ions, which are in turn bridged by [PdCl2(2-Clnic)2]2- (in (1)) or [PdBr2(2-Brnic)2]2- (in (2)) building blocks. On the contrary, the carboxylic groups are not deprotonated in the DMF/water mixture. Therefore, the carboxylic O atoms can’t coordinate to sodium ions, leading to the formation of simple palladium(II) monomers (3) and (4), which are further stabilized by O–H···O hydrogen bonds between their carboxylic groups and lattice DMF molecules. All the experimental findings were correlated and explained by DFT calculations.