Sorption of Xenon, Methane, and Organic Solvents by a Flexible Microporous Polymer Catena-Bis(Dibenzoylmethanato)-(4,4‘-bipyridyl)nickel(II)

The title polymeric complex, [Ni(bipy)(DBM) 2 ] (bipy = 4,4‘-bipyridyl; DBM = PhCOCHCOPh -, dibenzoylmethanate), absorbs considerable quantities of gases and organic solvents. This material presents special problems for characterization, as single crystals of suitable size could not be grown, and paramagnetism interferes with the usual NMR spectroscopic applications. To define the material adequately, an approach of structural analogy, along with the examination of the adsorbed guests by appropriate NMR techniques, was employed. The sorption of xenon follows an isotherm characteristic of microporous solids, with a plateau at 1:2 host-to-xenon molar ratio (68 mL of xenon per 1 g of sorbent) at ∼60 atm. The interaction with methane (>100 atm) results in an uptake of up to 0.8 mol methane (27 mL/g). Under ambient conditions the title compound absorbs a wide range of organic solvents, up to two moles, either from the vapor or by direct contact with liquids. Structural changes range from minor adjustments to total reorganization of the polymer crystal structure. The basic structural features of the [Ni(bipy)(DBM) 2 ]*2(chlorobenzene) inclusion compound are anticipated to be the same as those determined by an X-ray single-crystal study of its isostructural Zn-analogue. The DBM ligands chelate the Zn centers forming equatorial planes and the bipy ligands bridge the flat Zn(DBM) 2 units into linear polymeric chains to form a “wheel-and-axle” host motif, with guest species in the residual space. Deuterium NMR of the inclusion compound with benzene- d 6 gives direct evidence that it is an included guest in the crystalline lattice of [Ni(bipy)(DBM) 2 ].