Inclusion ability of 4-phenylpyridine-extended nickel(II) dibenzoylmethanate, a new metal-complex host

A new host complex, [Ni(4-PhPY)(2)(DBM)(2)], has been prepared by modification of nickel dibenzoylmethanate (Ni(DBM)(2); DBM = C6H5COCHCOC6H5-) with 4-phenylpyridine (4PhPy). Of 17 organic solvents that were tested as guest candidates, 6 inclusion compounds were isolated, mostly as bulk products. All compounds were characterized with XRD methods. With benzene, fluoro-, chloro-, and bromobenzenes, toluene, and o-xylene, 1: 1 inclusions form; they are all green, relatively stable, and isostructural (triclinic, P (1) over bar, Z = 2). The guest species accommodate flattened cages formed upon van der Waals packing of host molecules. The guest inclusion influences the distortion in the bischelate fragment of the host molecule, as the dihedral angle between two chelate rings ranges up to 12degrees. This distortion is probably responsible for the green color of these phases. The series of inclusions exhibits an order of thermal stability opposite to that which would be expected from the volativity of the neat guests; the order indicates strong preference of the inclusion matrix to benzenes with smaller substituents. With benzene, one more inclusion phase was isolated as a metastable product, with a host-to-guest ratio of 1:4; it is brown and of a distinct structural type (triclinic, P (1) over bar, Z = 1). The guest species are found in alternating layers of closely packed host molecules. The guest-free host phase is brown; its crystal structure (triclinic, P (1) over bar, Z = 1) is different from the inclusion compounds. In all the materials studied the host molecule is a transconfigured octahedral complex with two DBMs chelating the nickel(II) center in an equatorial plane and two 4-PhPy ligands coordinating axially.