Metal-Organic Frameworks with Hexakis(4-carboxyphenyl)benzene: Extensions to Reticular Chemistry and Introducing Foldable Nets.

ABSTRACT

Nine metal-organic frameworks have been prepared with the hexagon-shaped linker 1,2,3,4,5,6-hexakis(4-carboxyphenyl)benzene (H6cpb) by solvothermal reactions in dimethylformamide (dmf) or dimethylacetamide (dmac) with acetic acid or formic acid as modulators [Bi2(cpb)(acetato)2(dmf)2]·2dmf CTH-6 forms a rtl-net; 2(H2NMe2)[Cu2(cpb)] CTH-7 forms a kgd-net; [Fe4(cpb)(acetato)2(dmf)4] CTH-8 and [Co4(cpb)(acetato)2(dmf)4] CTH-9 are isostructural and form yav-nets; 2(HNEt3)[Fe2(cpb)] CTH-10 and the two polymorphs of 2(H2NMe2)[Zn2(cpb)]·1.5dmac, Zn-MOF-888 and CTH-11, show kgd-nets; [Cu2(cpb)(acetato)2(dmf)2]·2dmf, CTH-12, forms a mixed coordination and hydrogen-bonded sql-net; and 2(H2NMe2)[Zn2(cpb)] CTH-13, a similarly mixed yav-net. Surface area values (Brunauer-Emmett-Teller, BET) range from 34 m2 g-1 for CTH-12 to 303 m2 g-1 for CTH-9 for samples activated at 120 °C in dynamic vacuum. All compounds show normal (10-fold higher) molar CO2 versus N2 uptake at 298 K, except the 19-fold CO2 uptake for CTH-12 containing Cu(II) dinuclear paddle-wheels. We also show how perfect hexagons and triangles can combine to a new 3D topology laf, a model of which gave us the idea of foldable network topologies, as the laf-net can fold into a 2D form while retaining the local geometry around each vertex. Other foldable nets identified are cds, cds-a, ths, sqc163, clh, jem, and tfc covering the basic polygons and their combinations. The impact of this concept on "breathing" MOFs is discussed. I2 sorption, both from gas phase and from MeOH solution, into CTH-7 were studied by time of flight secondary ion mass spectrometry (ToF-SIMS) on dried crystals. I2 was shown to have penetrated the crystals, as layers were consecutively peeled off by the ion beam. We suggest ToF-SIMS to be a method for studying sorption depth profiles of MOFs.