We have applied crystal engineering as a tool to study the solid-state transformation from molecular saltsto coordination complexes via mechanochemical dehydrochlorination reactions.The-(CH2)n-(n = 2,3)alkyl chains were introduced into the bibenzylamine moiety to form the two nitrogen bases N,N,N′,N′-tetrabenzylethylenediamine(L1) and N,N,N′,N′-tetrabenzylpropydiamine(L2),which were self-assembled withtetrachlorometalates to form a series of supramolecular salts through second-sphere coordination.Single crystalsof salts [L1]2H+·[CuCl4]2-·solvent(1) and [L2]2H+·[XCl4]2-·solvent(2-4;X = Cu,Hg,Zn) were obtained and theirstructures determined by single-crystal X-ray diffraction.The effect of different alkyl chains(two and three-CH2-units) on the solid-state reactivity showed that the chelating complexes resulting from the mechanochemical dehydrohalogenation reaction depend on the formation of quasi-chelating hydrogen-bonding salts,Figure 1a.Quantum-mechanical calculations have been used to gain insight in this mechanochemical dehydrohalogenationreaction,demonstrating that not only is size matching between reactants is important but also conformationalenergies,intermolecular interactions,and the symmetry of frontier molecular orbitals play an important role.