Adeline Y. Robin

Of Chains and Rings: Synthetic Strategies and Theoretical Investigations for Tuning the Structure of Silver Coordination Compounds and Their Applications

Varying the polyethyleneglycol spacer between two (iso)-nicotinic groups of the ligand systems, a large structural variety of silver coordination compounds was obtained, starting with zero-dimensional ring systems, via one-dimensional chains, helices and double-helices to two-dimensional polycatenanes. Theoretical calculations help to understand their formation and allow predictions in some cases. These structures can be tuned by careful design of the ligand, the use of solvent and the counter ions, influencing also other important properties such as light stability and solubility. The latter is important in the context of biomedical applications, using silver compounds as antimicrobial agents.

Structural relationship of two coordination polymers of Cu(I) with the ligand ethanediyl bis(isonicotinate)

The flexible ligand ethanediyl bis(isonicotinate), L, is used as linking unit for Cu(I) ions in a coordination polymer. Two different structures of one-dimensional chains can be obtained, mainly depending on the co-crystallising solvent. Weak interactions such as hydrogen bonding and pi–stacking, and the exclusion of solvent molecules are responsible for the slow transformation of one compound into the other in the mother liquor.

How many structures are there for {[AgL](NO3)(H2O)n}? Water-content dependent variations in the structure of {[AgL](NO3)(H2O)n}, n= 0, 1, 2; L = ethanediyl bis(isonicotinate)

Three compounds of the composition [AgL](NO3)(H2O)n, n = 0 (1), 1 (2), 2 (3) have been obtained with different structures each. Whereas 1 builds single chains of ...–Ag–L–Ag–L–... crosslinked by NO3− anions to form two-dimensional layers, the conformation of L changes from anti to syn in 2, yielding pairs of chains with close Ag–Ag contacts. The anti conformation of the ligand L is again adopted in 3, and pairs of chains are now arranged in a parallel fashion. Calculations give a qualitative understanding of involved forces.

On the coordination behaviour of NO3- in coordination compounds with Ag+

The influence of the solubility of AgNO3 in three solvent systems is studied for the reaction between AgNO3 and the ligand L (= ethanediyl bis(isonicotinate)). Three solid state structures are obtained, differing in the relative ratio Ag : L in the first case, and in polymorphism in the second. The Ag–O(NO3−) distance correlates strongly with the solubility of AgNO3 in the used solvent. Solution studies prove indeed the existence of close ion contact pairs in the less good solvents, where as ion solvation is observed in good solvents for AgNO3. The three different structures are compared to two solvated structures in which H2O demonstrates coordination to the nitrate anion via H-bonding.

Concomitant crystallization of two polymorphs—a ring and a helix: concentration effect on supramolecular isomerism

For the first time in Ag coordination chemistry, two supramolecular isomers, a ring and a helix, are isolated from the same mother liquor as a result of concentration effects.