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The 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.

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The present work provides the basis to obtain three-dimensional (3D) extended porous supramolecular assemblies named supramolecular metal−organic frameworks (SMOFs). This goal can be achieved by considering three key factors: (i) the use of rigid building units, (ii) the establishment of predictable and rigid synthons between the building units, and (iii) the non-coplanarity of functional groups involved in the predictable synthons. Throughout this report we demonstrate the suitability of this synthetic strategy supported by six new SMOFs based on metal-nucleobase entities which fulfill the stated requirements: [Co(ThioG) 3 ] (SMOF-4; ThioG = thioguaninato), [Co(Hade) 2 X 2 ] (SMOF-5, SMOF-6; Hade = adenine and X = Cl − , Br − ), [Cu 8 (μ 3 -OH) 4 (μ 4 -OH) 4 (ade) 4 (μ-ade) 4 (μ-Hade) 2 ] (SMOF-7; ade = adeninato), [Cu 4 (μ 3 -ade) 4 (μade) 2 (pentylNH 2 ) 2 (CH 3 OH) 2 (CO 3 ) 2 (H 2 O) 2 ] (SMOF-8; pentylNH 2 = 1-pentylamine), and [Cu 2 (μ-ade) 2 (ade)(μ-OH)(H 2 O)(CH 3 OH)] n (SMOF-9). SMOF-4 is built up from monomeric entities in which bidentate thioguaninato ligands establish complementary hydrogen bonding interactions in non-coplanar directions leading to supramolecular layers that are further connected resulting in a porous structure with one-dimensional (1D) channels. The hydrogen bonding interactions among Watson−Crick and sugar edges of monomeric entities in SMOF-5 give rise to a triply interpenetrated supramolecular framework. Octameric clusters in SMOF-7 are self-assembled by hydrogen bonding to yield a porous 3D network. SMOF-8 is built up from tetranuclear units that are linked via base pairing interactions involving Watson−Crick faces to afford layers whose assembly generates a twodimensional pore system. SMOF-9 is in between pure MOFs and SMOFs since it consists of 1D infinite coordination polymers held together by complementary hydrogen bonding interactions into a 3D supramolecular porous structure.

Five new compounds of cytosine with first-row transition metals, (H 2 Cyt) 2 [CoCl 4 ]·2(HCyt) (1), [CoBr 2 (HCyt) 2 ] (2), [ZnCl 2 (HCyt) 2 ] (3), [CuCl 2 (HCyt) 2 ] (4), and [CuBr 2 (HCyt) 2 ] (5) (in which HCyt = cytosine, H 2 Cyt = cytosinium cation), are reported. In 1, the protonation of one of the cytosine molecules facilitates base pairing with the neutral cytosine, instead of the expected coordination to the metal center. In all other compounds, neutral cytosine molecules are coordinated to the M II centers through N3 positions, forming monomeric entities. The supramolecular crystal structure of 1 is sustained by the basepairing interactions between the 1H,3H-cytosinium cation and [a]