Novel 4-vinylpyridine-extended metal-dibenzoylmethanate host frameworks: structure, polymorphism, and inclusion properties.

In this contribution we show that host materials based on metal dibenzoylmethanates (DBM) can be extended in a versatile way by decreasing the packing efficiency of the simpler metal DBM's reported earlier. Specifically, this can be accomplished by coordinating two 4-vinylpyridines (4-ViPy) to the metal (Ni or Co) DBM units to give [M(4-ViPy)2(DBM)2] host complexes. These display a remarkable polymorphism and an ability to form inclusion compounds with a large variety of organic species. Five non-clathrate phases representing three polymorphic types and twenty-eight inclusion compounds with nineteen guests, representing five structural types were isolated and studied in varying degrees of detail. The inclusion compounds can be prepared by recrystallization or by interaction of the solid host with guest vapor. In the latter case, the process realization, kinetics and final product strongly depend on the host polymorph chosen as starting material. Kinetic studies executed with powder XRD suggest that transient formation of inclusion compounds may occur even during solvent vapor induced transformation of one guest-free polymorph to another. The beta polymorph of the Ni-host reveals the strongest clathratogenic ability as well as a high selectivity towards certain homologues and isomers. Its properties give insight into the concept of "flexible zeolite mimics", or "apohosts", as this empty host form is energetically and structurally predisposed towards inclusion processes. In all eleven (three host and eight clathrate) structures studied by single crystal X-ray diffraction the [M(4-Vi-Py)2(DBM)2] complex molecule is transconfigured. In most, the host molecules show effective packing in one dimension by forming parallel chains. Guest species are located between the chains in cages or channels formed by combining voids in the host molecules belonging to adjacent chains. The corresponding Ni and Co versions of the compounds studied were similar.