Self-Assembly of Multinuclear Coordination Species with Chiral Bipyridine Ligands: Silver Complexes of 5,6-CHIRAGEN(o,m,p-xylidene) Ligands and Equilibrium Behaviour in Solution

Abstract

The complexation reactions between Ag- and a series of enantiopure ligands belonging to the CHIRAGEN (from CHIRAlity GENerator) family (L1, L2, L3, based on (-)-5,6-pinene bipyridine) have been studied in solution. It has been shown that the length of the bridge plays a fundamental role in the self-assembly processes leading to different compounds: mononuclear complexes (with L3), mixtures of polynuclear complexes (with L2) and circular helicates (with L 1). Although the absolute configuration of the chiral centres in all three ligands is the same, the metal-centred chirality of L3 (delta) is inverted with respect to that in the other two complexes with L1 and L2 (delta). The metal configuration is thus opposite in the mononuclear complex with respect to the polynuclear species. Detailed thermodynamic studies were carried out for the Ag+ and L1 ligand system by 1H and 109Ag NMR spectroscopy (as a function of concentration, temperature and pressure). At low temperature and high pressure, the [Ag6L1(6)]6+ hexanuclear circular helicate forms a tetranuclear circular helicate [Ag4L1(4)]4+: 2[Ag6L1(6)]6+ <=> 3 [Ag4L1(4)]4+. The thermodynamics parameters, obtained by temperature and pressure variation, have the following values: K298 = (8.7 +/- 0.7) x 10(-5) mol x kg(-1), deltaHo = -15.65 +/- 0.8 kJ x mol(-1), deltaSo = -130.2 +/- 3 J x mol(-1) x K(-1) and deltaVo(256 K)= -160 +/- 12 cm3 x mol(-1). The reaction volume calculated according to Connolly's method indicates that the calculated structure of [Ag4L1(4)]4+ is plausible. Both the signs and large magnitudes of deltaSo and deltaVo are counterintuitive, yet can be understood by modelling methods.

Hydrostatic Pressure on Toroidal Interaction and Propeller Chirality of Hexaarylbenzenes: Explicit Solvent Effects on Differential Volumes in Methylcyclohexane and Hexane

“…The Δ V value of +195 cm 3 mol −1 was reported for the calix[5]arene/fullerene complex, where two solvent (toluene) molecules are displaced upon complexation . The silver complex of chiral bipyridine ligands also exhibited the large Δ V of −160 cm 3 mol −1 , reflecting the transformation from a tetramer to a hexamer . In other typical complex formation processes, the Δ V values are at least one order of magnitude smaller and are expressively varied depending on the complex composition, nature of interaction, and other factors such as solvation and other environmental variants.…”

Self‐Assembly of Cyclohelicate [M3L3] Triangles Over [M4L4] Squares, Despite Near‐Linear Bis‐terdentate L and Octahedral M

“…This observation may provide some insight into some previously puzzling results, where larger cyclohelicate assemblies were reported to be entropically favored, a result described by those authors as counterintuitive, but one which might be explained by low frequency vibrational modes tipping the overall entropy in favor of the larger molecular assemblies. That is, the dominance of the vibrational contribution to the overall entropy, as shown herein, indicates that the different vibrational properties of the different sized cyclohelicates may influence the entropic preference to such an extent that particle counting arguments are not sufficient to explain the observed product.…”

Maßgeschneiderte Moleküle für Selbstorganisationsreaktionen: gezielte Herstellung zweier chiraler, selbstorganisierter Spezies mit vorherbestimmter Konfiguration

“…Die negative Reaktionsentropie dagegen ist nur schwer verständlich, da sowohl die Teilchenzahl, als auch die Zahl der stereochemischen Realisierungsmöglichkeiten bei der Bildung des Trimers zunimmt. Das gleiche unerwartete Verhalten wurde kürzlich für das Gleichgewicht zwischen der hexameren und der tetrameren Form eines silberhaltigen Circularhelicates beschrieben 5…”