Chair−Boat Form Transformation of Piperazine-Containing Ligand toward the Preparation of Dirhenium Metallacycles

A new generation of a flexible bipyridine-based ligand, 1,4-bis(4-pyridyl)-piperazine, with two main stable states (chair and twist-boat forms) was employed in the construction of unusual dirhenium metallacycles

Dissolution/Reorganization toward the Destruction/Construction of Porous Cobalt(II)− and Nickel(II)−Carboxylate Coordination Polymers

The alkali-metal-cation-induced structural transformation of porous coordination polymers (CPs), {A2[M3(btec)2(H2O)4]}n (1, A = K, M = Co; 2, A = K, M = Ni; 3, A = Cs, M = Co; and 4, A = Cs, M = Ni; btec = benzene-1,2,4,5-tetracarboxylate), occurred via a unique dissolution/reorganization process in the presence of an alkali chloride (LiCl, NaCl) in water. Treatment of 1 or 2 in an aqueous solution of LiCl resulted in the formation of new metal−carboxylate species [Co2(btec)(H2O)10]·H2O (5·H2O) and {Li2[Ni3(btec)2(H2O)10]·3.5H2O}n (6·3.5H2O), respectively. When NaCl was used in place of LiCl under similar reaction conditions, similar dissolution/reorganization processes were observed. The cobalt species 1 and 3 were converted into the metal−carboxylate product [Na2Co(btec)(H2O)8]n (7), whereas the nickel−carboxylate frameworks 2 and 4 were transformed into {[Na4Ni2(btec)2(H2O)18]·3H2O}n (8·3H2O). Single-crystal X-ray diffraction analysis revealed that 5·H2O is a discrete molecule, which extends to a hydrogen-bonded 3D porous supramolecular network including tetrameric water aggregates. Compound 6·3.5H2O adopts a 3D polymeric structure with a novel (2,4,4)-connected net on the basis of a 4-connecting organic node of a btec ligand, a square-planar 4-connecting metallic trans-Ni(O2C)4(H2O)2 node, and a 2-connecting octahedral metallic trans-Ni(O2C)2(H2O)4 hinge. Compound 7 possesses a 3D polymeric structure comprised of two types of intercrossed (4,4)-layers, a [CoII(btec)]-based layer and a [NaI(btec)]-based layer, in a nearly perpendicular orientation (ca. 87°). Compound 8·3H2O adopted a 2D sheet network by utilizing heterometallic trinuclear clusters of Na2Ni(O2C)5(H2O)9 as secondary building units. Each sheet is hydrogen-bonded to neighboring units, giving a 3D supramolecular network. It is noteworthy that the dissolution/reorganization process demonstrates the cleavage and reformation of metal−carboxylate bonds, leading to a destruction/construction structural transformation of CPs

Dissolution/Reorganization toward the Destruction/Construction of Porous Cobalt(II)− and Nickel(II)−Carboxylate Coordination Polymers

The alkali-metal-cation-induced structural transformation of porous coordination polymers (CPs), {A2[M3(btec)2(H2O)4]}n (1, A = K, M = Co; 2, A = K, M = Ni; 3, A = Cs, M = Co; and 4, A = Cs, M = Ni; btec = benzene-1,2,4,5-tetracarboxylate), occurred via a unique dissolution/reorganization process in the presence of an alkali chloride (LiCl, NaCl) in water. Treatment of 1 or 2 in an aqueous solution of LiCl resulted in the formation of new metal−carboxylate species [Co2(btec)(H2O)10]·H2O (5·H2O) and {Li2[Ni3(btec)2(H2O)10]·3.5H2O}n (6·3.5H2O), respectively. When NaCl was used in place of LiCl under similar reaction conditions, similar dissolution/reorganization processes were observed. The cobalt species 1 and 3 were converted into the metal−carboxylate product [Na2Co(btec)(H2O)8]n (7), whereas the nickel−carboxylate frameworks 2 and 4 were transformed into {[Na4Ni2(btec)2(H2O)18]·3H2O}n (8·3H2O). Single-crystal X-ray diffraction analysis revealed that 5·H2O is a discrete molecule, which extends to a hydrogen-bonded 3D porous supramolecular network including tetrameric water aggregates. Compound 6·3.5H2O adopts a 3D polymeric structure with a novel (2,4,4)-connected net on the basis of a 4-connecting organic node of a btec ligand, a square-planar 4-connecting metallic trans-Ni(O2C)4(H2O)2 node, and a 2-connecting octahedral metallic trans-Ni(O2C)2(H2O)4 hinge. Compound 7 possesses a 3D polymeric structure comprised of two types of intercrossed (4,4)-layers, a [CoII(btec)]-based layer and a [NaI(btec)]-based layer, in a nearly perpendicular orientation (ca. 87°). Compound 8·3H2O adopted a 2D sheet network by utilizing heterometallic trinuclear clusters of Na2Ni(O2C)5(H2O)9 as secondary building units. Each sheet is hydrogen-bonded to neighboring units, giving a 3D supramolecular network. It is noteworthy that the dissolution/reorganization process demonstrates the cleavage and reformation of metal−carboxylate bonds, leading to a destruction/construction structural transformation of CPs

[Cd^II(bpdc)·H₂O]<i>_n</i>: A Robust, Thermally Stable Porous Framework through a Combination of a 2-D Grid and a Cadmium Dicarboxylate Cluster Chain (H₂bpdc = 2,2‘-Bipyridyl-4,4‘-dicarboxylic Acid)

The synthesis and characterization of a cadmium(II) coordination polymer, [Cd(C12H6N2O4)·H2O]n (1), is reported. A single-crystal X-ray analysis shows that compound 1 presents a noninterpenetrating three-dimensional porous host containing one-dimensional hydrophilic channels, where guest water molecules reside. The strategy in designing the 3-D framework architecture is based on a combination of two building subunits:  a porous two-dimensional grid of (4,4) topology and a metal dicarboxylate cluster chain. Both subunits are assembled from the coordination of a cadmium ion with a three-connecting organic modular ligand, 2,2‘-bipyridyl-4,4‘-dicarboxylic acid (H2bpdc). The results of thermogravimetric analysis and powder X-ray diffraction study show that the framework rigidity of compound 1 remains intact upon the removal of guest molecules, and maintains the thermal stability up to 440 °C. The second-row transition-metal ions are capable of engaging higher coordination modes (e.g., hepta- and octacoordination) because of their atomic sizes and intrinsic electron configurations. Our results show that the heptacoordinated cadmium center plays an important role in the overall framework rigidity and high thermal stability of compound 1. Crystal data for 1:  Cd(C12H6N2O4)·H2O, triclinic, space group P1̄, a = 6.7843(5) Å, b = 9.3299(7) Å, c = 9.4439(7) Å, α = 104.629(1)°, β = 92.324(1)°, γ = 100.416(1)°, Z = 2

An Unprecedentedly Huge Square-Grid Copper(II)−Organic Framework Material Built from a Bulky Pyrene-Derived Elongated Cross-Shaped Scaffold

A new bulky pyrene-derived elongated cross-shaped organic scaffold was successfully incorporated into a highly porous, noninterpenetrated square-grid copper(II)−organic framework material with the unprecedentedly huge dimensions of 25.5 × 25.5 Å2, while the layer-to-layer NH···N interaction leads to a unique hydrogen-bonded 64.82-nbo net

[Cd^II(bpdc)·H₂O]<i>_n</i>: A Robust, Thermally Stable Porous Framework through a Combination of a 2-D Grid and a Cadmium Dicarboxylate Cluster Chain (H₂bpdc = 2,2‘-Bipyridyl-4,4‘-dicarboxylic Acid)

The synthesis and characterization of a cadmium(II) coordination polymer, [Cd(C12H6N2O4)·H2O]n (1), is reported. A single-crystal X-ray analysis shows that compound 1 presents a noninterpenetrating three-dimensional porous host containing one-dimensional hydrophilic channels, where guest water molecules reside. The strategy in designing the 3-D framework architecture is based on a combination of two building subunits:  a porous two-dimensional grid of (4,4) topology and a metal dicarboxylate cluster chain. Both subunits are assembled from the coordination of a cadmium ion with a three-connecting organic modular ligand, 2,2‘-bipyridyl-4,4‘-dicarboxylic acid (H2bpdc). The results of thermogravimetric analysis and powder X-ray diffraction study show that the framework rigidity of compound 1 remains intact upon the removal of guest molecules, and maintains the thermal stability up to 440 °C. The second-row transition-metal ions are capable of engaging higher coordination modes (e.g., hepta- and octacoordination) because of their atomic sizes and intrinsic electron configurations. Our results show that the heptacoordinated cadmium center plays an important role in the overall framework rigidity and high thermal stability of compound 1. Crystal data for 1:  Cd(C12H6N2O4)·H2O, triclinic, space group P1̄, a = 6.7843(5) Å, b = 9.3299(7) Å, c = 9.4439(7) Å, α = 104.629(1)°, β = 92.324(1)°, γ = 100.416(1)°, Z = 2

Spin-Canting Magnetization in an Unusual Co₄ Cluster-Based Layer Compound from a 2,3-Dihydroxyquinoxaline Ligand

The self-assembly of Co­(O2CPh)2 with a 2,3-dihydroxyquinoxaline (H2dhq) linker has revealed a new two-dimensional cluster-based compound, [Co4(OMe)2(O2CPh)2(dhq)2(MeOH)2]n, which shows spin-canted magnetization and a definite magnetic hysteresis loop

Spin-Canting Magnetization in an Unusual Co₄ Cluster-Based Layer Compound from a 2,3-Dihydroxyquinoxaline Ligand

The self-assembly of Co­(O₂CPh)₂ with a 2,3-dihydroxyquinoxaline (H₂dhq) linker has revealed a new two-dimensional cluster-based compound, [Co₄(OMe)₂(O₂CPh)₂(dhq)₂(MeOH)₂]_<i>n</i>, which shows spin-canted magnetization and a definite magnetic hysteresis loop

Unusual Robust Luminescent Porous Frameworks Self-Assembled from Lanthanide Ions and 2,2‘-Bipyridine-4,4‘-dicarboxylate

Three lanthanide(III) coordination polymers, [{Ln2(bpdc)3(H2O)3}·H2O]n (Ln = Sm, 1; Eu, 2; Tb, 3), were self-assembled from 2,2‘-bipyridine-4,4‘-dicarboxylic acid (H2bpdc) and corresponding lanthanide(III) salts under hydrothermal conditions. The compounds were found to be isomorphous and isostructural. Single-crystal X-ray diffraction studies show that compounds 1−3 present a three-dimensional network with one-dimensional hydrophilic microchannels that are occupied by guest water molecules. An edge-sharing dinuclear polyhedral [Ln2O14] was found to be the building unit of the network, in which two eight-coordinated LnO8 cores exhibit distinct coordination environments, that is, one is in a dicapped trigonal prism and the other is in a dodecahedron. Surprisingly, the bpdc ligand exhibits four different types of bonding characteristics in a framework, including the bis(monodentate), bis(syn,syn-bridging bidentate), bis(syn,anti-bridging bidentate), and bis(chelating-bridging bidentate) modes. The pyridyl nitrogen atoms of the 2,2‘-bipyridyl unit in the bpdc ligand are uncoordinated in an anti conformation along the central C−C bond of the ligand, resulting from the high oxophilic nature of lanthanide(III) ions. A thermogravimetric analysis of 1 showed a high thermal stability (decomposing under N2 at T > 470 °C), indicating that the coordination habit of the metal ions with the bpdc ligand has a profound effect on the overall rigidity of the framework and the thermal stability of the compound. Photoluminescence measurements indicate that europium compound 2 and terbium compound 3 are strong red and green emitters, respectively