One-pot mechanosynthesis with three levels of molecular self-assembly: Coordination bonds, hydrogen bonds and host-guest inclusion

Liquid-assisted grinding (LAG) was used to combine three levels of molecular self-assembly into a one-pot mechanochemical approach for the construction of metal–organic materials. The approach was applied for the construction of three adducts of cobalt(II) dibenzoylmethanate with isonicotinamide, nicotinamide and imidazole, to screen for their inclusion compounds. The one-pot process consists of: i) The coordination-driven binding of addends to the equatorially-protected metal ion, resulting in “wheel-and-axle”-shaped complexes; ii) self-assembly of resulting complexes by way of hydrogen-bonded synthons to form metal–organic inclusion hosts; iii) in situ inclusion of the grinding liquid in the resulting host. This approach provided quantitatively and within 20 min the known inclusion compounds of the bis(isonicotinamide) adduct in a single synthetic step. Changing the liquid phase in LAG was used to explore the inclusion behaviour of new wheel-and-axle adducts with nicotinamide and imidazole, revealing several inclusion compounds, as well as two polymorphs, of the bis(nicotinamide) host. Preliminary results suggest that one-pot LAG is superior to solution synthesis in screening for metal–organic inclusion compounds. The difference between the methods is rationalised in terms of reactant solubility and solvent competition. In contrast to the nicotinamide adduct, the bis(imidazole) adduct did not form inclusion compounds. The difference in the inclusion properties of the two adducts is rationalised by structural information gathered by single crystal and powder X-ray diffraction.