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>

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

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

Synthetic Control to Achieve Lanthanide(III)/Pyrimidine-4,6-dicarboxylate Compounds by Preventing Oxalate Formation: Structural, Magnetic, and Luminescent Properties

Control over the synthetic conditions in many metal/diazinedicarboxylato systems is crucial to prevent oxalate formation, since dicarboxylato ligands easily undergo degradation in the presence of metal salts. We report here an efficient route to obtain oxalato-free compounds for the lanthanide/pyrimidine-4,6-dicarboxylato (pmdc) system on the basis of the reaction temperature and nonacidic pH or oxygen free atmosphere. Two different crystal architectures have been obtained: {[Ln­(μ-pmdc)_1.5(H₂O)₃]·<i>x</i>H₂O}_<i>n</i> (<b>1-Ln</b>) and {[Ln₂(μ₄-pmdc)₂(μ-pmdc)­(H₂O)₂]·H₂O}_<i>n</i> (<b>2-Ln</b>) with Ln­(III) = La–Yb, except Pm. Both crystal structures are built from distorted two-dimensional honeycomb networks based on the recurrent double chelating mode established by the pmdc. In compounds <b>1-Ln</b>, the tricapped trigonal prismatic coordination environment of the lanthanides is completed by three water molecules, precluding a further increase in the dimensionality. Crystallization water molecules are arranged in the interlamellar space, giving rise to highly flexible supramolecular clusters that are responsible for the modulation found in compound <b>1-Gd</b>. Two of the coordinated water molecules are replaced by nonchelating carboxylate oxygen atoms of pmdc ligands in compounds <b>2-Ln</b>, joining the metal–organic layers together and thus providing a compact three-dimensional network. The crystal structure of the compounds is governed by the competition between two opposing factors: the ionic size and the reaction temperature. The lanthanide contraction rejects the sterically hindered coordination geometries whereas high-temperature entropy driven desolvation pathway favors the release of solvent molecules leading to more compact frameworks. The characteristic luminescence of the Nd, Eu, and Tb centers is improved when moving from <b>1-Ln</b> to <b>2-Ln</b> compounds as a consequence of the decrease of the O–H oscillators. The magnetic properties of the compounds are dominated by the spin–orbit coupling and the ligand field perturbation, the exchange coupling being almost negligible

Synthetic Control to Achieve Lanthanide(III)/Pyrimidine-4,6-dicarboxylate Compounds by Preventing Oxalate Formation: Structural, Magnetic, and Luminescent Properties

Control over the synthetic conditions in many metal/diazinedicarboxylato systems is crucial to prevent oxalate formation, since dicarboxylato ligands easily undergo degradation in the presence of metal salts. We report here an efficient route to obtain oxalato-free compounds for the lanthanide/pyrimidine-4,6-dicarboxylato (pmdc) system on the basis of the reaction temperature and nonacidic pH or oxygen free atmosphere. Two different crystal architectures have been obtained: {[Ln­(μ-pmdc)_1.5(H₂O)₃]·<i>x</i>H₂O}_<i>n</i> (<b>1-Ln</b>) and {[Ln₂(μ₄-pmdc)₂(μ-pmdc)­(H₂O)₂]·H₂O}_<i>n</i> (<b>2-Ln</b>) with Ln­(III) = La–Yb, except Pm. Both crystal structures are built from distorted two-dimensional honeycomb networks based on the recurrent double chelating mode established by the pmdc. In compounds <b>1-Ln</b>, the tricapped trigonal prismatic coordination environment of the lanthanides is completed by three water molecules, precluding a further increase in the dimensionality. Crystallization water molecules are arranged in the interlamellar space, giving rise to highly flexible supramolecular clusters that are responsible for the modulation found in compound <b>1-Gd</b>. Two of the coordinated water molecules are replaced by nonchelating carboxylate oxygen atoms of pmdc ligands in compounds <b>2-Ln</b>, joining the metal–organic layers together and thus providing a compact three-dimensional network. The crystal structure of the compounds is governed by the competition between two opposing factors: the ionic size and the reaction temperature. The lanthanide contraction rejects the sterically hindered coordination geometries whereas high-temperature entropy driven desolvation pathway favors the release of solvent molecules leading to more compact frameworks. The characteristic luminescence of the Nd, Eu, and Tb centers is improved when moving from <b>1-Ln</b> to <b>2-Ln</b> compounds as a consequence of the decrease of the O–H oscillators. The magnetic properties of the compounds are dominated by the spin–orbit coupling and the ligand field perturbation, the exchange coupling being almost negligible

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