Stabilization of guest-free forms of metal dibenzoylmethanate host type through self-inclusion of a ligand fragment into the intramolecular pocket

A derivative of the metal dibenzoylmethanate (DBM) host type, accomplished through the chemical modification of the DBM ligand, is reported for the first time. The new ligand, (1-naphthoyl)benzoylmethanate (NBM) differs from the parent DBM by an additional phenylene ring. Three new complexes [NiA₂(NBM)₂], with pyridine (Py), 4-methylpyridine (4-MePy) and 4-phenylpyridine (4-PhPy) is A, were synthesized and studied for host properties. Complexes with Py and 4-MePy were isolated as solvent-free forms and did not show any ability to form inclusion compounds with ten solvents tested. Single-crystal XRD study revealed van der Waals type of crystal structure of the complexes. The nickel atom is octahedrally coordinated by two chelating NBMs in the equatorial plane and two terminal pyridines. Naphthyl ligands turn almost perpendicular to the equatorial plane of the complex filling the pocket space which usually accommodates guest species in metal DBM analogues. This ‘self-inclusion’ of its own fragment, that the molecule demonstrates, explains the inability of the complexes to entrap guest solvents. The complex with 4-PhPy forms inclusion compounds with chloroform, benzene, tetrahydrofuran and acetone, the compounds have 1:2 host to guest ratio and are isostructural. A possible explanation of such a difference is the larger size of the pocket which now cannot be completely filled with the naphthyl fragment.