Chasing weak forces: hierarchically assembled helicates as a probe for the evaluation of the energetics of weak interactions
D. Van Craen, W.H. Rath, M. Huth, L. Kemp, C. Räuber, J. Wollschläger, C.A. Schalley, A. Valkonen, K. Rissanen, M. Albrecht – 2017
London dispersion forces are the weakest interactions between molecules. Due to this , their influence on chemical processes is often low, but can definitely not be ignored and even becomes important in case 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 besides 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. Thus, besides the enthalpic benefit of London dispersion, the entropy loss becomes significant in case of long alkyl substituents and results in an entropic destabilization of the dimeric helicates.