Syntheses, Crystal Structures and Adsorption Properties of Ultramicroporous Coordination Polymers Constructed from Hexafluorosilicate Ions and Pyrazine

Three novel coordination polymers based on M2+ (M = Cu, Zn), pyrazine (pyz) and the SiF62- ion, [Cu(SiF6)(pyz)(H2O)(2)](n) (1a), {[Cu(SiF6)(pyz)(3)]center dot 2H(2)O}(n) (1b superset of 2H(2)O) and {[Zn(SiF6)(pyz)(2)]center dot 2MeOH}(n) (2 superset of 2MeOH), have been synthesized and characterized by single-crystal X-ray diffraction analyses. Compound la forms straight one-dimensional chains of -Cu(OH2)(2)-pyz-, which are bridged by SiF62- ions to produce two-dimensional sheets. Compound 1b superset of 2H(2)O forms straight two-dimensional sheets of -Cu(pyz)(2)-pyz- chains bridged by SiF62- ions, where perpendicularly protruding pyz planes are stacked to produce a three-dimensional framework with 2.5 x 2.2 angstrom(2) pores. In compound 2 superset of 2MeOH, grids of [Zn(pyz)(2)](n) are bridged by SiF62- ions axially coordinating to Zn2+ ions to produce an open three-dimensional framework. The 4.5 x 4.5 angstrom(2) pores in 2 superset of 2MeOH are surrounded by pyz panels, and they remain intact after removal of solvents to give [Zn(SiF6)(pyz)(2)](n) (2). The permanent porosity of 2 was characterized by adsorption studies with solvent vapours such as MeOH (kinetic diameter 3.8 angstrom), EtOH (4.3 angstrom), iPrOH (4.7 angstrom) and Me2CO (4.7 angstrom), showing a size-exclusive effect at around 4.7 angstrom. Furthermore, the H-2 adsorption/desorption isotherm of 2 at 77 K shows a sharp uptake with a slight hysteresis loop, which is attributed to both the small size of the pore and the interaction between H-2 molecules and fluorine (SiF62-) atoms that are exposed on the pore surfaces. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)