Chasing Weak Forces: Hierarchically Assembled Helicates as a Probe for the Evaluation of the Energetics of Weak Interactions

London
dispersion forces are the weakest interactions between molecules.
Because of this, their influence on chemical processes is often low,
but can definitely not be ignored, and even becomes important in cases
of molecules with large contact surfaces. Hierarchically assembled
dinuclear titanium­(IV) helicates represent a rare example in which
the direct observation of London dispersion forces is possible in
solution even in the presence of strong cohesive solvent effects.
Hereby, the dispersion forces do not unlimitedly support the formation
of the dimeric complexes. Although they have some favorable enthalpic
contribution to the dimerization of the monomeric complex units, large
flexible substituents become conformationally restricted by the interactions
leading to an entropic disadvantage. The dimeric helicates are entropically
destabilized.