Stages of Kitaigorodsky Aufbau Principle Detached in the Cocrystals of Cp₂MX₂(M = Ti, Zr; X = Cl, Br, I) with σ- And π-Hole Donors

Organometallic halogenides Cp2MX2 (M = Ti, Zr; X = Cl, Br, I) were utilized as σ- and π-hole acceptors in interaction with deficient perfluoroarenes. The chain assembly of Cp2MX2 molecules stabilized by H-X hydrogen bonds, characteristic for their native crystals, recur unchanged in their 1:1 cocrystals with 1,4-DITFB. The arrangement between the Cp2MX2 and 1,4-DITFB chains in the cocrystals clearly depends on the directionality of lone electron pairs of halogen X. These series of cocrystals let us speak about the supramolecular dissolution, which is reverse to the Kitaigorodsky's Aufbau Principle, used for the analysis and prediction of molecular crystal packing. The latter suggests four stages of aggregation on the way from individual molecules (stage 0) to the 3D crystal lattice (stage 3). Two stages, which are in between, operate with 1D molecular stacks and 2D molecular layers, which are more like representations rather than real entities in the crystal. However, in the process of supramolecular dissolution, these feebly associated molecules, chains, and layers appear as detached, individual, and quite objective entities.