Unravelling the Growth of Supramolecular Metal–Organic Frameworks Based on Metal-Nucleobase Entities

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] (<b>SMOF-4</b>; ThioG = thioguaninato), [Co­(Hade)₂X₂] (<b>SMOF-5</b>, <b>SMOF</b>-<b>6</b>; Hade = adenine and X = Cl^–, Br^–), [Cu₈(μ₃-OH)₄­(μ₄-OH)₄­(ade)₄­(μ-ade)₄­(μ-Hade)₂] (<b>SMOF-7</b>; ade = adeninato), [Cu₄(μ₃-ade)₄­(μ-ade)₂­(pentylNH₂)₂­(CH₃OH)₂­(CO₃)₂­(H₂O)₂] (<b>SMOF-8</b>; pentylNH₂ = 1-pentylamine), and [Cu₂(μ-ade)₂­(ade)­(μ-OH)­(H₂O)­(CH₃OH)]_<i>n</i> (<b>SMOF-9</b>). <b>SMOF-4</b> 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 <b>SMOF-5</b> give rise to a triply interpenetrated supramolecular framework. Octameric clusters in <b>SMOF-7</b> are self-assembled by hydrogen bonding to yield a porous 3D network. <b>SMOF-8</b> is built up from tetranuclear units that are linked via base pairing interactions involving Watson–Crick faces to afford layers whose assembly generates a two-dimensional pore system. <b>SMOF-9</b> 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

3D Magnetically Ordered Open Supramolecular Architectures Based on Ferrimagnetic Cu/Adenine/Hydroxide Heptameric Wheels

The present work provides two new examples of supramolecular metal–organic frameworks consisting of three-dimensional extended noncovalent assemblies of wheel-shaped heptanuclear [Cu₇(μ-H₂O)₆(μ₃-OH)₆­(μ-adeninato-κ<i>N</i>3:κ<i>N</i>9)₆]²⁺ entities. The heptanuclear entity consists of a central [Cu­(OH)₆]^4– core connected to six additional copper­(II) metal centers in a radial and planar arrangement through the hydroxides. It generates a wheel-shaped entity in which water molecules and μ–κ<i>N</i>3:κ<i>N</i>9 adeninato ligands bridge the peripheral copper atoms. The magnetic characterization indicates the central copper­(II) center is anti-ferromagnetically coupled to external copper­(II) centers, which are ferromagnetically coupled among them leading to an <i>S</i> = 5/2 ground state. The packing of these entities is sustained by π–π stacking interactions between the adenine nucleobases and by hydrogen bonds established among the hydroxide ligands, sulfate anions, and adenine nucleobases. The sum of both types of supramolecular interactions creates a rigid synthon that in combination with the rigidity of the heptameric entity generates an open supramolecular structure (40–50% of available space) in which additional sulfate and triethylammonium ions are located altogether with solvent molecules. These compounds represent an interesting example of materials combining both porosity and magnetic relevant features

3D Magnetically Ordered Open Supramolecular Architectures Based on Ferrimagnetic Cu/Adenine/Hydroxide Heptameric Wheels

The present work provides two new examples of supramolecular metal–organic frameworks consisting of three-dimensional extended noncovalent assemblies of wheel-shaped heptanuclear [Cu₇(μ-H₂O)₆(μ₃-OH)₆­(μ-adeninato-κ<i>N</i>3:κ<i>N</i>9)₆]²⁺ entities. The heptanuclear entity consists of a central [Cu­(OH)₆]^4– core connected to six additional copper­(II) metal centers in a radial and planar arrangement through the hydroxides. It generates a wheel-shaped entity in which water molecules and μ–κ<i>N</i>3:κ<i>N</i>9 adeninato ligands bridge the peripheral copper atoms. The magnetic characterization indicates the central copper­(II) center is anti-ferromagnetically coupled to external copper­(II) centers, which are ferromagnetically coupled among them leading to an <i>S</i> = 5/2 ground state. The packing of these entities is sustained by π–π stacking interactions between the adenine nucleobases and by hydrogen bonds established among the hydroxide ligands, sulfate anions, and adenine nucleobases. The sum of both types of supramolecular interactions creates a rigid synthon that in combination with the rigidity of the heptameric entity generates an open supramolecular structure (40–50% of available space) in which additional sulfate and triethylammonium ions are located altogether with solvent molecules. These compounds represent an interesting example of materials combining both porosity and magnetic relevant features