Designing Multifunctional 5‑Cyanoisophthalate-Based Coordination Polymers as Single-Molecule Magnets, Adsorbents, and Luminescent Materials

Detailed structural, magnetic, and photoluminescence characterization of a family of new compounds based on 5-cyanoisophthalate (CNip) ligand and several transition metal or lanthanide ions, namely, [Cu₃(μ₃-CNip)₂(μ-H₂O)₂(μ₃-OH)₂]_<i>n</i> (<b>1</b>), {[Co₃(μ₄-CNip)₃(DMF)₄]·∼2DMF}_<i>n</i> (<b>2</b>), [Cd­(μ₄-CNip)­ (DMF)]_<i>n</i> (<b>3</b>), {[Ln₂(μ₄-CNip)­(μ₃-CNip)₂(DMF)₄]·∼DMF·H₂O}_<i>n</i> (<b>4-Ln</b>) (with Ln^III = Tb, Dy, and Er), {[Gd₆(μ₃-CNip)₅(μ₄-CNip)₃(μ-form)₂(H₂O) (DMF)₁₀]·∼3DMF·3H₂O}_<i>n</i> (<b>5</b>), {[Zn₃₂(μ₄-CNip)₁₂(μ-CNip)₁₂(μ₄-O)₈(H₂O)₂₄]·∼12DMF}_<i>n</i> (<b>6</b>) (where DMF = dimethylformamide, form = formate), is reported. The large structural diversity found in the system may be explained mainly in terms of the coordination characteristics that are inherent to the employed metal ions, the coordination versatility of the dicarboxylic ligand and the synthetic conditions. Interestingly, some crystal structures (three-dimensional (3D) frameworks of <b>4-Ln</b> and <b>5</b> and 3D network of <b>6</b>) exhibit open architectures containing large solvent-occupied void systems, among which <b>5</b> reveals permanent porosity as confirmed by N₂ adsorption measurements at 77 K. Magnetic direct current (dc) susceptibility data on compounds <b>1</b>, <b>2</b>, and <b>5</b> were measured. Moreover, compounds <b>2</b>, <b>4-Dy</b>, <b>4-Er</b>, and <b>5</b> show slow magnetic relaxation, from which it is worth highlighting the effective energy barrier of 44 K at zero dc field for the dysprosium counterpart. Compound <b>5</b> also deserves to be mentioned given the few 3D Gd-organic frameworks reported examples. Photophysical properties were also accomplished at different temperatures, confirming both the fluorescent emission of 5-cyanoisophthalate ligands when coordinated to cadmium ions in <b>3</b> and their capacity to sensitize the long-lived fluorescence of the selected lanthanide ions in <b>4-Ln</b>. Broken symmetry and time-dependent density functional theory computational calculations support the experimental luminescence and magnetic properties

Directing the Formation of Adenine Coordination Polymers from Tunable Copper(II)/Dicarboxylato/Adenine Paddle-Wheel Building Units

Coordination polymers containing paddle-wheel shaped building units of general formula [Cu₂(μ-adeninato)₂(μ-carboxylato)₂] (<b>1</b>–<b>3</b>) and [Cu₂(μ-carboxylato)₄(methyladenine)₂] (<b>4</b>–<b>6</b>) are reported. The copper­(II) centers of the compounds {[Cu₂(μ₃-adeninato)₂(μ-Hglut)₂]·2H₂O}_<i>n</i> (<b>1</b>), {[Cu₂(μ₃-adeninato)₂(μ-Hadip)₂]}_<i>n</i> (<b>2</b>), and {[Cu₂(μ₃-adeninato)₂(μ-Hpime)₂]}_<i>n</i> (<b>3</b>) (where glut: glutarato; adip: adipato; and pime: pimelato) are bridged by tridentate <i>N3,N7,N9</i>-adeninato ligands to give a similar covalent three-dimensional network in which the dicarboxylate anions act as bidentate μ-κ<i>O1</i>:κ<i>O2</i> ligands with a free hydrogencarboxylic group placed within the channels present in the crystal structures. In <b>2</b>–<b>3</b>, the −COOH group of the pendant aliphatic chain is hydrogen bonded to the Watson–Crick face (N6H/N1) of an adenine nucleobase placed at the opposite side of the channel, whereas in <b>1</b>, the shorter aliphatic chain precludes this interaction and crystallization water molecules are placed between the hydrogencarboxylic group and the nucleobase. Compounds {[Cu₂(μ₄-glut)₂(3Meade)₂]·4H₂O}_<i>n</i> (<b>4</b>), {[Cu₂(μ₄-glut)₂(9Meade)₂]}_<i>n</i> (<b>5</b>), and {[Cu₂(μ₄-pime)₂(9Meade)₂]·2H₂pime}_<i>n</i> (<b>6</b>) (where 3Meade: 3-methyladenine and 9Meade: 9-methyladenine) contain neutral chains where the paddle-wheel motifs are doubly bridged by tetratopic dicarboxylate anions. The supramolecular architecture of <b>4</b> and <b>5</b> is essentially knitted by hydrogen bonding interactions between the Watson–Crick faces of adjacent adenines, whereas compound <b>6</b> shows the inclusion of guest pimelic molecules which are anchored to the polymeric chains through fork-like hydrogen bonding interactions between one of the carboxylic groups and the peripheral adenine moieties, affording a supramolecular layered structure. The magnetic data of all the compounds show the occurrence of an antiferromagnetic behavior which is dominated by the orbital complementarity of the adenine and carboxylato bridging ligands in compounds <b>1</b>–<b>3</b>

Structure-Directing Effect of Organic Cations in the Assembly of Anionic In(III)/Diazinedicarboxylate Architectures

We report herein the synthesis and physicochemical characterization of seven new indium–pyrazine-2,5-dicarboxylato (pzdc) and pyridazine-3,6-dicarboxylato (pddc) compounds: (dma)₆[In₆(μ-pzdc)₁₂]·<i>x</i>H₂O (<b>1</b>), (dea)₆[In₆(μ-pzdc)₁₂]·<i>x</i>H₂O (<b>2</b>), {(tma)­[In­(μ-pzdc)₂]·2H₂O}_<i>n</i> (<b>3</b>), {(dea)­[In­(μ-pzdc)₂]·2H₂O}_<i>n</i> (<b>4</b>), {(dma)­[In­(μ-pddc)₂]·<i>x</i>H₂O}_<i>n</i> (<b>5</b>), {(dma)­[In­(μ-pddc)₂]}_<i>n</i> (<b>6</b>), and (dma)₄[In₈(μ-pddc)₁₂(H₂O)₈(OH)₄]·<i>x</i>H₂O (<b>7</b>) (where dma = dimethylammonium, dea = diethylammonium, tma = tetramethylammonium). Two types of In­(III)/pzdc structures have been obtained. The first one (<b>1</b> and <b>2</b>) is comprised of discrete hexanuclear anionic assemblies held together by hydrogen bonding interactions through the organic cations generated by the thermal hydrolysis of the amide solvents. The second one (<b>3</b> and <b>4</b>) consists of an anionic three-dimensional (3D) framework with channels that are occupied by the counterions and solvent molecules. The first type of structure seems to be the kinetically preferred one since it is obtained when using relatively soft solvothermal conditions (120 °C) and counterions that are able to establish relatively strong hydrogen bonding interactions. The 3D frameworks crystallize when the organic counterion is unable to establish hydrogen bonding interactions or when employing a higher temperature (150 °C). The metal–organic assemblies obtained in the In­(III)/pddc system range from two-dimensional (2D) sheets (<b>5</b> and <b>6</b>) to discrete octameric entities (<b>7</b>) depending on the amount of water in the reaction mixture. It is worth noting that the open lamellar crystal structure of compound <b>5</b> undergoes a solid state transformation accompanied by the release of water molecules, rendering the solvent free 2D architecture of <b>6</b> that exhibits a different connectivity. Surprisingly, a prolonged exposure of <b>6</b> to a water saturated atmosphere does not revert to <b>5</b> but promotes a partial and reversible transformation to give a new unidentified In-pddc compound

Directing the Formation of Adenine Coordination Polymers from Tunable Copper(II)/Dicarboxylato/Adenine Paddle-Wheel Building Units

Coordination polymers containing paddle-wheel shaped building units of general formula [Cu₂(μ-adeninato)₂(μ-carboxylato)₂] (<b>1</b>–<b>3</b>) and [Cu₂(μ-carboxylato)₄(methyladenine)₂] (<b>4</b>–<b>6</b>) are reported. The copper­(II) centers of the compounds {[Cu₂(μ₃-adeninato)₂(μ-Hglut)₂]·2H₂O}_<i>n</i> (<b>1</b>), {[Cu₂(μ₃-adeninato)₂(μ-Hadip)₂]}_<i>n</i> (<b>2</b>), and {[Cu₂(μ₃-adeninato)₂(μ-Hpime)₂]}_<i>n</i> (<b>3</b>) (where glut: glutarato; adip: adipato; and pime: pimelato) are bridged by tridentate <i>N3,N7,N9</i>-adeninato ligands to give a similar covalent three-dimensional network in which the dicarboxylate anions act as bidentate μ-κ<i>O1</i>:κ<i>O2</i> ligands with a free hydrogencarboxylic group placed within the channels present in the crystal structures. In <b>2</b>–<b>3</b>, the −COOH group of the pendant aliphatic chain is hydrogen bonded to the Watson–Crick face (N6H/N1) of an adenine nucleobase placed at the opposite side of the channel, whereas in <b>1</b>, the shorter aliphatic chain precludes this interaction and crystallization water molecules are placed between the hydrogencarboxylic group and the nucleobase. Compounds {[Cu₂(μ₄-glut)₂(3Meade)₂]·4H₂O}_<i>n</i> (<b>4</b>), {[Cu₂(μ₄-glut)₂(9Meade)₂]}_<i>n</i> (<b>5</b>), and {[Cu₂(μ₄-pime)₂(9Meade)₂]·2H₂pime}_<i>n</i> (<b>6</b>) (where 3Meade: 3-methyladenine and 9Meade: 9-methyladenine) contain neutral chains where the paddle-wheel motifs are doubly bridged by tetratopic dicarboxylate anions. The supramolecular architecture of <b>4</b> and <b>5</b> is essentially knitted by hydrogen bonding interactions between the Watson–Crick faces of adjacent adenines, whereas compound <b>6</b> shows the inclusion of guest pimelic molecules which are anchored to the polymeric chains through fork-like hydrogen bonding interactions between one of the carboxylic groups and the peripheral adenine moieties, affording a supramolecular layered structure. The magnetic data of all the compounds show the occurrence of an antiferromagnetic behavior which is dominated by the orbital complementarity of the adenine and carboxylato bridging ligands in compounds <b>1</b>–<b>3</b>

Structural Diversity in a Copper(II)/Isophthalato/9-Methyladenine System. From One- to Three-Dimensional Metal-Biomolecule Frameworks

The synthesis, X-ray single crystal structure analyses, and physicochemical characterization of copper­(II)-isophthalato coordination polymers containing the 9-methyladenine nucleobase {[Cu­(μ-iso)­(9Meade)­(H₂O)₂]}_<i>n</i> (<b>1</b>), {[Cu­(μ-iso)­(μ-9Meade)]}_<i>n</i> (<b>2</b>), {[Cu₂(μ₄-iso)₂­(9Meade)₂]­·2H₂iso}_<i>n</i> (<b>3</b>), {[Cu₂(μ₃-iso)₂­(μ-9Meade)­(H₂O)]·H₂O}_<i>n</i> (<b>4</b>), and {[Cu₂(μ₃-iso)₂­(μ-9Meade)­(H₂O)₂]­·1.5H₂O}_<i>n</i> (<b>5</b>) (where iso = isophthalato and 9Meade = 9-methyladenine) are reported. Compound <b>1</b> contains neutral chains in which the isophthalato dianion acts as a bridging ligand, while the methylated nucleobase behaves as N7-coordinated terminal ligand. Compound <b>2</b> exhibits a two-dimensional network in which the aromatic dicarboxylate ligand and the nucleobase act as bidentate bridging ligands. Compound <b>3</b> is based on dimeric paddle-wheel shaped entities in which the copper­(II) atoms are bridged by means of four isophthalato ligands to give a NO₄ chromophore with the N7 nitrogen atom of the 9-methyladenine filling the axial position. The linkage of the dimeric entities through the second carboxylate group of the dianions leads to covalent layers that are further connected to give a supramolecular three-dimensional pillared structure by means of hydrogen bonding and π–π interactions involving noncoordinated isophthalic acid molecules. Compounds <b>4</b> and <b>5</b> contain paddle-wheel [Cu₂(μ-iso)₄­(9Meade)₂] entities and [Cu­(H₂O)] or [Cu­(H₂O)₂] units connected by means of the isophthalate and 9-methyladenine bidentate bridging ligands

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

Porous Supramolecular Architectures Based on π‑Stacking Interactions between Discrete Metal-Adenine Entities and the Non-DNA Theobromine/Caffeine Nucleobases

This work is aimed at the analysis of the π–π stacking interactions as the driving force to develop porous supramolecular metal–organic frameworks (SMOFs) as an alternative to more directional hydrogen bonding interactions. Four compounds based on the interaction between rigid copper/adenine entities and theobromine/caffeine molecules have been synthesized: [Cu₇(μ-ade)₆­(μ₃-OH)₆­(μ-H₂O)₆]­(theo)₂­·<b>∼</b>28H₂O (<b>1</b>), [Cu₂(μ-ade)₄­(H₂O)₂]­·3Htheo­·<b>∼</b>7H₂O (<b>2</b>), [Cu₂(μ-ade)₄­(H₂O)₂]­·2Htheo­·<b>∼</b>18H₂O (<b>3</b>), and [Cu₂(μ-ade)₄­(H₂O)₂]­·(caf)­·∼6H₂O (<b>4</b>). The blue compound <b>1</b> is formed by wheel-shaped cationic heptameric units where the copper atoms are bridged by hydroxide anions, water molecules, and adeninato ligands with a μ-κ<i>N3</i>:κ<i>N9</i> coordination mode. The assembly of the heptameric entities and the theobrominate anions takes place mainly through π–π stacking interactions involving the adeninato ligands and theobrominate moieties. Although compound <b>1</b> exhibits an open-framework with voids representing 37% of the unit cell, the plasticity of the π–π interactions causes a reversible shrinkage of the porous system upon activation that precludes the adsorption of gas molecules. Dark purple compounds <b>2</b>–<b>4</b> contain neutral windmill units in which two copper atoms are bridged by four μ-κ<i>N3</i>:κ<i>N9</i> adeninato ligands. Their final crystal structure highly depends on the supramolecular interactions of the theobromine and caffeine molecules. In compound <b>2</b>, two theobromine molecules are hydrogen bonded to the Hoogsteen face of two trans-arranged adeninato ligands, whereas a third theobromine molecule is joined to the Watson–Crick face of one of the previous adeninato ligands. In compound <b>3</b>, with a lower amount of theobromine, the Watson–Crick interaction is not present. In both compounds, the three-dimensional (3D) crystal structure requires the additional presence of π–π stacks between the theobromine molecules. In compound <b>4</b>, as the methyl groups of the caffeine molecule do not allow hydrogen bond interactions, the adeninato ligands are hydrogen bonded among them to generate, together with π-stacking interactions, two-dimensional supramolecular sheets containing rectangular windows in which the caffeine molecules are located. Only compound <b>4</b> showed permanent porosity, adsorbing a significant amount of CO₂ (0.88 mmol of CO₂/g at 5 bar and 273 K). The magnetic characterization of these compounds indicates a ferrimagnetic behavior for <b>1</b> and strong intradimeric antiferromagnetic interactions in compounds <b>2</b> and <b>4</b>

Combining Polycarboxylate and Bipyridyl-like Ligands in the Design of Luminescent Zinc and Cadmium Based Metal–Organic Frameworks

Detailed structural characterization and photoluminescence properties of four new metal–organic frameworks (MOFs) based on zinc­(II) or cadmium­(II) metal ions, di- or tricarboxylic aromatic ligands, and bipyridyl-like elongated ancillary linkers, namely, {[Zn₂(μ₄-bdc)₂­(μ-pbptz)]­·2DMF­·3H₂O}_<i>n</i> (<b>1</b>), {[Cd­(μ₃-bdc)­(μ-pbptz)]­·3DMF}_<i>n</i> (<b>2</b>), {[Cd₃(μ₅-btc)₂­(μ-pbptz)]­·2DMF}_<i>n</i> (<b>3</b>), and {[Zn₂(μ-dhbdc)₂­(μ-pbptz)­(DMF)₄]­·2DMF·H₂O}_<i>n</i> (<b>4</b>) (where bdc = benzene-1,4-dicarboxylato, btc = benzene-1,3,5-tricarboxylato, dhbdc = 2,5-dihydroxobenzene-1,4-dicarboxylato, pbptz = 3,6-bis­(4-pyridyl)-1,2,4,5-tetrazine, DMF = <i>N</i>,<i>N</i>-dimethylformamide) are reported. The occurrence of large accessible volumes and structural and topological diversity are a constant for crystal structures of these compounds, which is a result of the connectivity established among the metal-carboxylato building units formed in each case. Three-dimensional (3D) <b>pcu</b> frameworks of compounds <b>1</b> and <b>2</b> are built from the linkage of dimeric cores (established by the coordination of dicarboxylato bdc ligands) into two-dimensional networks that are further joined together by ancillary ligands, whereas the novel <b>jcr7</b> topological 3D framework is achieved in <b>3</b> owing to the presence of the tricarboxylic btc ligand. Two-dimensional layers are generated in <b>4</b> given the bidentate coordination of both dhbdc and pbptz ligands. Interestingly, most crystal structures (3D frameworks of <b>1</b>, <b>2</b>, and <b>3</b>) exhibit open architectures containing large solvent-occupied void systems that account for high relative void volumes. A deep analysis of the photophysical properties has been also accomplished for all compounds, confirming an overall blue emission under UV excitation in the steady state. Compound <b>3</b> is characterized with a strong phosphorescent emission that lasts a few seconds and is observed by the naked eye, which constitutes an infrequent photoluminescent behavior for metal–organic materials

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