cg500634y_si_001.pdf (1.09 MB)
Paddle-Wheel Shaped Copper(II)-Adenine Discrete Entities As Supramolecular Building Blocks To Afford Porous Supramolecular Metal–Organic Frameworks (SMOFs)
journal contribution
posted on 2014-08-06, 00:00 authored by Jintha Thomas-Gipson, Garikoitz Beobide, Oscar Castillo, Michael Fröba, Frank Hoffmann, Antonio Luque, Sonia Pérez-Yáñez, Pascual RománThe
present work assesses the ability of [Cu2(μ-adenine)4(X)2]2+ and [Cu2(μ-adenine)2(μ-X)2(X)2] (X: Cl– or Br–) metal-nucleobase dinuclear
entities to build up supramolecular metal–organic frameworks
(SupraMOFs) based on the complementary hydrogen bonding interactions
established by the Watson–Crick and Hoogsteen faces of adjacent
adenine moieties. The noncoplanar disposition of these synthons in
the [Cu2(μ-adenine)4(X)2]2+ building unit leads to an open framework with one-dimensional
(1D) channels of ca. 6 Å in compounds [Cu2(μ-adenine)4(Cl)2]Cl2·∼2MeOH (1, SMOF-1) and [Cu2(μ-adenine)4(Br)2]Br2·∼2 MeOH
(2, SMOF-2) sustained through the hydrogen
bonding base pairing interactions among the Watson–Crick faces.
In the case of the second building unit, [Cu2(μ-adenine)2(μ-X)2(X)2], the coplanar
arrangement of the two adenines in the dimeric unit does not allow
a three-dimensional (3D) supramolecular architecture based only on
the complementary hydrogen bonding interactions between the nucleobases.
Therefore, other supramolecular interactions involving the halide
ions and solvent molecules are crucial for determining the features
of the crystal packing. In compound [Cu2(μ-adenine)2(μ-Cl)2(Cl)2]·2MeOH
(3, SMOF-3), base pairing interactions between
adjacent adenines produce 1D supramolecular ribbons of dinuclear entities.
These ribbons establish additional hydrogen bonds between the Hoogsteen
face and the chloride anions of adjacent ribbons that are also reinforced
by the presence of π–π stacking interactions among
the adenines leading to a rigid synthon that gives rise to a robust
3D skeleton with the presence of micropores occupied by solvent molecules.
In the case of the bromide analogue, the weaker hydrogen acceptor
capacity of the bromide allows the solvent molecules to disrupt the
self-assembly process of the dinuclear entities and prevents the formation
of an open-framework supramolecular structure leading to the nonporous
[Cu2(μ-adenine)2(μ-Br)2(Br)2]·2PrOH (4)
compound. According to gas adsorption studies, SMOF-1, SMOF-2, and SMOF-3 present a surface
instability that creates a diffusion barrier that can be permeated
only by strong interacting adsorbate molecules with high kinetic energy
such as CO2 but not N2, H2, and CH4. This feature makes them attractive for selective gas adsorption
and separation technologies.
