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

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.