From Simple Palladium(II) Monomers to 2D Heterometallic Sodium–Palladium(II) Coordination Networks with 2‑Halonicotinates

The 2D heterometallic sodium–palladium(II) coordination
polymers with 2-halonicotinates [2-chloropyridine-3-carboxylate (2-chloronicotinate),
2-Clnic– and 2-bromopyridine-3-carboxylate (2-bromonicotinate),
2-Brnic–], {[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 prepared in aqueous solutions under
the presence of NaHCO3, while palladium(II) monomers with
the neutral 2-chloronicotinic and 2-bromonicotinic acid ligands, [PdCl2(2-ClnicH-N)2]·2DMF (3) and [PdCl2(2-BrnicH-N)2]·2DMF (4), were prepared in DMF/water mixtures
(DMF = N,N′-dimethylformamide).
The zigzag chains of water-bridged sodium ions are in turn bridged
by [PdCl2(2-Clnic)2]2– moieties
in 1 or by [PdBr2(2-Brnic)2]2– moieties in 2, leading to the formation
of the infinite 2D coordination networks of 1 or 2. The DFT calculations showed the halosubstituents type (Cl vs Br) does not have an influence on the formation of either trans or cis isomers. The trans isomers were found in all reported compounds; being more stable
for about 10 to 15 kJ mol–1. The 2D coordination
networks 1 and 2 are more stabilized by
the formation of Na–Ocarboxylate bonds, comparing
to the stabilization of palladium(II) monomers 3 and 4 by hydrogen-bonding with DMF molecules. The difference in
DFT calculated energy stabilization for 1 and 2 is ascribed to the type of halosubstituents and to the presence/absence
of lattice water molecules in 1 and 2. The
compounds show no antibacterial activity toward reference strains
of Escherichia coli and Staphylococcus aureus bacteria and no antiproliferative
activity toward bladder (T24) and lung (A549) cancer cell lines.