Characterization of persistent intramolecular C-H⋅⋅⋅X(N,O) bonds in solid state and solution

The formation of intramolecular CH⋅⋅⋅X(N,O) bonds and their persistence in solution were studied by X-ray crystallography and NMR techniques in two different rotamers of a molecule containing the ortho-carborane cage, an amide group and a quinoline ring. Experimental data were confirmed by theoretical ab initio calculations. From the resolved structure of the two forms of this potentially active drug for boron neutron capture therapy, accurate bonding and geometric parameters were extracted for this non-classic hydrogen interaction, and their strength was calculated. These findings provided new insight in the theory of CH⋅⋅⋅X bonds, which appear stronger and less rare than it was previously thought.