Iodine Release and Recovery, Influence of Polyiodide Anions on Electrical Conductivity and Nonlinear Optical Activity in an Interdigitated and Interpenetrated Bipillared-Bilayer Metal–Organic Framework

{[Cu₆(pybz)₈(OH)₂]·I₅^–·I₇^–}_<i>n</i> (<b>1</b>), obtained hydrothermally by using iodine molecules as a versatile precursor template, consists of a cationic framework with two types of zigzag channels, which segregate I₅^– and I₇^– anions. The framework exhibits the first observed bipillared-bilayer structure featuring both interdigitation and interpenetration. <b>1</b> displays high framework stability in both acidic (HCl) and alkaline (NaOH) solutions. <b>1</b> slowly releases iodine in dry methanol to give [Cu₆(pybz)₈(OH)₂]­(I^–)₂·3.5CH₃OH (<b>1</b>′) and partially recovers iodine from cyclohexane to form [Cu₆(pybz)₈(OH)₂]­(I^–)₂·<i>x</i>I₂ (<b>1</b>″). Differences of up to 100 times in electrical conductivity and of 4 times in nonlinear optical activity (NLO) have been measured between <b>1</b> and <b>1</b>′. This compound is one of few displaying multifunctionality, electrical conductivity, NLO, and crystal–crystal stability upon release and recovery of iodine. It is also unique in the iodine release from polyiodide anions in a metal–organic framework

Iodine Release and Recovery, Influence of Polyiodide Anions on Electrical Conductivity and Nonlinear Optical Activity in an Interdigitated and Interpenetrated Bipillared-Bilayer Metal–Organic Framework

{[Cu₆(pybz)₈(OH)₂]·I₅^–·I₇^–}_<i>n</i> (<b>1</b>), obtained hydrothermally by using iodine molecules as a versatile precursor template, consists of a cationic framework with two types of zigzag channels, which segregate I₅^– and I₇^– anions. The framework exhibits the first observed bipillared-bilayer structure featuring both interdigitation and interpenetration. <b>1</b> displays high framework stability in both acidic (HCl) and alkaline (NaOH) solutions. <b>1</b> slowly releases iodine in dry methanol to give [Cu₆(pybz)₈(OH)₂]­(I^–)₂·3.5CH₃OH (<b>1</b>′) and partially recovers iodine from cyclohexane to form [Cu₆(pybz)₈(OH)₂]­(I^–)₂·<i>x</i>I₂ (<b>1</b>″). Differences of up to 100 times in electrical conductivity and of 4 times in nonlinear optical activity (NLO) have been measured between <b>1</b> and <b>1</b>′. This compound is one of few displaying multifunctionality, electrical conductivity, NLO, and crystal–crystal stability upon release and recovery of iodine. It is also unique in the iodine release from polyiodide anions in a metal–organic framework

Ligand Effect on the Single-Molecule Magnetism of Tetranuclear Co(II) Cubane

A clear dependence on the ligand has been observed for the magnetic properties of a closely related series of Co­(II) cubane structures, viz. [Co₄(<i>mbm</i> or <i>bm</i>)₄(ROH)₄Br₄] (<b>1-MeOH</b>, <b>1-EtOH</b>, <b>2-MeOH</b>, and <b>2-EtOH</b>, where <b>1</b> = [Co₄(<i>mbm</i>)₄Br₄], <b>2</b> = [Co₄(<i>bm</i>)₄Br₄], <i>bm</i> = (1<i>H</i>-benzo­[<i>d</i>]­imidazol-2-yl)­methanolate. and <i>mbm</i> = 1-Me-<i>bm</i>.) The [Co₄(OR)₄] cubane core consists of an octahedral Co^II center chelated by the alkoxide oxygen and imidazole nitrogen atoms from monoanionic <i>bm</i> or <i>mbm</i> and coordinated by methanol/alcohol and bromine. Interestingly, electrospray ionization mass spectrometry (ESI-MS) indicates that <b>1-MeOH</b> and <b>2-MeOH</b> are unstable in methanol and transformed to the butterfly [Co₄L₆]²⁺ but that <b>1-EtOH</b> and <b>2-EtOH</b> are stable in ethanol. Their magnetic susceptibilities suggest ferromagnetic coupling between the nearest cobalt centers to give a theoretical <i>S</i> = 4 × 3/2 ground state with considerable magneto-crystalline behavior. The packing and intermolecular interactions appear to influence the geometry of the cubes and thus the anisotropy of cobalt, which leads to different blocking temperatures (<i>T</i>_B). Consequently, the compounds with <i>mbm</i>, <b>1-MeOH</b> and <b>1-EtOH</b>, exhibit <i>T</i>_B > 2 K as shown by the relaxation of magnetization in zero applied dc field where the barriers <i>U</i>_eff/<i>k</i>_B are respectively 27 and 21 K and relaxation times are τ₀ = 1.3 × 10^–9 and 9.7 × 10^–9 s. However, the compounds with <i>bm</i>, <b>2-MeOH</b> and <b>2-EtOH</b>, remain paramagnetic above 2 K and do not show nonlinear response of the ac susceptibilities. These findings reaffirm the subtle dependence of single-molecule magnetism on coordination geometry and intermolecular interaction

A Porous 4‑Fold-Interpenetrated Chiral Framework Exhibiting Vapochromism, Single-Crystal-to-Single-Crystal Solvent Exchange, Gas Sorption, and a Poisoning Effect

The synthesis and characterization of a 4-fold-interpenetrated pseudodiamond metal–organic framework (MOF), Co^II(pybz)₂·2DMF [pybz = 4-(4-pyridyl)­benzoate], are reported. <i>N</i>,<i>N</i>-Dimethylformamide (DMF) of the channels can be removed to give the porous framework, and it can also be exchanged for methanol, ethanol, benzene, and cyclohexane. It is a rare example of a stable MOF based on a single octahedral building unit. The single-crystal structures of Co^II(pybz)₂·2DMF, Co^II(pybz)₂, Co^II(pybz)₂·4MeOH, and Co^II(pybz)₂·2.5EtOH have been successfully determined. In all of them, the framework is marginally modified and contains a highly distorted and strained octahedral node of cobalt with two pyridine nitrogen atoms and two chelate carboxylate groups. In air, the crystals of Co^II(pybz)₂·2DMF readily change color from claret red to light pink. Thermogravimetric analysis and Raman spectroscopy indicate a change in coordination, where the carboxylate becomes monodentate and an additional two water molecules are coordinated to each cobalt atom. In a dry solvent, this transformation does not take place. Tests show that Co^II(pybz)₂ may be a more efficient drying agent than silica gel and anhydrous CuSO₄. The desolvated Co^II(pybz)₂ can absorb several gases such as CO₂, N₂, H₂, and CH₄ and also vapors of methanol, ethanol, benzene, and cyclohexane. If Co^II(pybz)₂ is exposed to air and followed by reactivation, its sorption capacity is considerably reduced, which we associate with a poisoning effect. Because of the long distance between the cobalt atoms in the structure, the magnetic properties are those of a paramagnet

Porous Supramolecular Networks Constructed of One-Dimensional Metal–Organic Chains: Carbon Dioxide and Iodine Capture

In search of porous materials for selective sorption and iodine inclusion, we have found two networks made of chains with a kink at the metal nodes held together by supramolecular interactions (H-bond and π···π stacking). The solvent can be removed and replaced reversibly without loss of crystallinity, as demonstrated by single-crystal-to-single-crystal crystallography. In contrast, iodine uptake degrades the crystallinity to amorphous, and it regains its crystalline state after removal of the iodine at 200 °C. Slight differences in behavior of the sorption and inclusion properties between the tetrahedral metal nodes, Zn and Co, are associated with the size of the nodes. An important feature is the extent of iodine that can be included between the chains that is doubled with temperature from 30 to 100 °C and exceeds the weight in mass of the compounds

Tracking the Formation of a Polynuclear Co₁₆ Complex and Its Elimination and Substitution Reactions by Mass Spectroscopy and Crystallography

We present the syntheses and structures of the biggest chiral cobalt coordination cluster, [Co₁₆(L)₄­(H₃L)₈­(N₃)₆]­(NO₃)₂·​16H₂O·​2CH₃OH (<b>1</b>, where H₄L = <i>S,S</i>-1,2-bis­(1<i>H</i>-benz­imidazol-2-yl)-1,2-ethane­diol). <b>1</b> consists of two Co₄O₄ cubes (Co₄(L)₂­(H₃L)₂) alternating with Co₂(EO-N₃)₂Co₂ (Co₄(L)₂­(H₃L)₂­(N₃)₂), bridged by the benzimidazole and azide nitrogen atoms to form a twisted ring. The ligand adopts both <i>cis</i> and <i>trans</i> forms, and all the rings have the same chiralilty. ESI-MS of <b>1</b> from a methanol solution of crystals reveals the fragment [Co₁₆(L)₄­(H₃L)₈­(N₃)₆+2H]⁴⁺, suggesting the polynuclear core is stable in solution. ESI-MS measurements from the reaction solution found smaller fragments, [Co₄­(H₃L)₄–H]³⁺, [Co₄­(H₃L)₄–2H]²⁺, [Co₄­(H₃L)₄­(N₃)₂]²⁺, and [Co₂­(H₃L)₂]²⁺, and ESI-MS from a methanol solution of the solid deposit found in addition the Co₁₆ core. These results and the dependence on the synthesis time allow us to propose the process for the formation of <b>1</b>, which opens up a new way for the direct observation of the ligand-controlled assembly of clusters. In addition, the isolation of [Co₄­(H₃L)₄]­(NO₃)₄·​4H₂O (<b>2</b>) consisting of separate Co₄O₄ cubes with the ligands being only <i>cis</i> in crystalline form supports the proposal. Interestingly, N₃^ is replaced by either CH₃O^– or OH^–, and this is the first time that high-resolution ESI-MS is successfully utilized to examine both the step-by-step elimination and substitution of inner bridging ligands in such a high nuclear complex. Increasing the voltage results in stepwise elimination of azide from the parent cluster. The preliminary magnetic susceptibility of <b>1</b> indicates ferromagnetic cubes antiferromagnetically coupled to the squares within the cluster, though in a field of 2.5 kOe, weak and slow relaxation is observed below 4 K

Tracking the Formation of a Polynuclear Co₁₆ Complex and Its Elimination and Substitution Reactions by Mass Spectroscopy and Crystallography

We present the syntheses and structures of the biggest chiral cobalt coordination cluster, [Co₁₆(L)₄­(H₃L)₈­(N₃)₆]­(NO₃)₂·​16H₂O·​2CH₃OH (<b>1</b>, where H₄L = <i>S,S</i>-1,2-bis­(1<i>H</i>-benz­imidazol-2-yl)-1,2-ethane­diol). <b>1</b> consists of two Co₄O₄ cubes (Co₄(L)₂­(H₃L)₂) alternating with Co₂(EO-N₃)₂Co₂ (Co₄(L)₂­(H₃L)₂­(N₃)₂), bridged by the benzimidazole and azide nitrogen atoms to form a twisted ring. The ligand adopts both <i>cis</i> and <i>trans</i> forms, and all the rings have the same chiralilty. ESI-MS of <b>1</b> from a methanol solution of crystals reveals the fragment [Co₁₆(L)₄­(H₃L)₈­(N₃)₆+2H]⁴⁺, suggesting the polynuclear core is stable in solution. ESI-MS measurements from the reaction solution found smaller fragments, [Co₄­(H₃L)₄–H]³⁺, [Co₄­(H₃L)₄–2H]²⁺, [Co₄­(H₃L)₄­(N₃)₂]²⁺, and [Co₂­(H₃L)₂]²⁺, and ESI-MS from a methanol solution of the solid deposit found in addition the Co₁₆ core. These results and the dependence on the synthesis time allow us to propose the process for the formation of <b>1</b>, which opens up a new way for the direct observation of the ligand-controlled assembly of clusters. In addition, the isolation of [Co₄­(H₃L)₄]­(NO₃)₄·​4H₂O (<b>2</b>) consisting of separate Co₄O₄ cubes with the ligands being only <i>cis</i> in crystalline form supports the proposal. Interestingly, N₃^ is replaced by either CH₃O^– or OH^–, and this is the first time that high-resolution ESI-MS is successfully utilized to examine both the step-by-step elimination and substitution of inner bridging ligands in such a high nuclear complex. Increasing the voltage results in stepwise elimination of azide from the parent cluster. The preliminary magnetic susceptibility of <b>1</b> indicates ferromagnetic cubes antiferromagnetically coupled to the squares within the cluster, though in a field of 2.5 kOe, weak and slow relaxation is observed below 4 K

A Porous 4‑Fold-Interpenetrated Chiral Framework Exhibiting Vapochromism, Single-Crystal-to-Single-Crystal Solvent Exchange, Gas Sorption, and a Poisoning Effect

The synthesis and characterization of a 4-fold-interpenetrated pseudodiamond metal–organic framework (MOF), Co^II(pybz)₂·2DMF [pybz = 4-(4-pyridyl)­benzoate], are reported. <i>N</i>,<i>N</i>-Dimethylformamide (DMF) of the channels can be removed to give the porous framework, and it can also be exchanged for methanol, ethanol, benzene, and cyclohexane. It is a rare example of a stable MOF based on a single octahedral building unit. The single-crystal structures of Co^II(pybz)₂·2DMF, Co^II(pybz)₂, Co^II(pybz)₂·4MeOH, and Co^II(pybz)₂·2.5EtOH have been successfully determined. In all of them, the framework is marginally modified and contains a highly distorted and strained octahedral node of cobalt with two pyridine nitrogen atoms and two chelate carboxylate groups. In air, the crystals of Co^II(pybz)₂·2DMF readily change color from claret red to light pink. Thermogravimetric analysis and Raman spectroscopy indicate a change in coordination, where the carboxylate becomes monodentate and an additional two water molecules are coordinated to each cobalt atom. In a dry solvent, this transformation does not take place. Tests show that Co^II(pybz)₂ may be a more efficient drying agent than silica gel and anhydrous CuSO₄. The desolvated Co^II(pybz)₂ can absorb several gases such as CO₂, N₂, H₂, and CH₄ and also vapors of methanol, ethanol, benzene, and cyclohexane. If Co^II(pybz)₂ is exposed to air and followed by reactivation, its sorption capacity is considerably reduced, which we associate with a poisoning effect. Because of the long distance between the cobalt atoms in the structure, the magnetic properties are those of a paramagnet

Tracking the Formation of a Polynuclear Co₁₆ Complex and Its Elimination and Substitution Reactions by Mass Spectroscopy and Crystallography

We present the syntheses and structures of the biggest chiral cobalt coordination cluster, [Co₁₆(L)₄­(H₃L)₈­(N₃)₆]­(NO₃)₂·​16H₂O·​2CH₃OH (<b>1</b>, where H₄L = <i>S,S</i>-1,2-bis­(1<i>H</i>-benz­imidazol-2-yl)-1,2-ethane­diol). <b>1</b> consists of two Co₄O₄ cubes (Co₄(L)₂­(H₃L)₂) alternating with Co₂(EO-N₃)₂Co₂ (Co₄(L)₂­(H₃L)₂­(N₃)₂), bridged by the benzimidazole and azide nitrogen atoms to form a twisted ring. The ligand adopts both <i>cis</i> and <i>trans</i> forms, and all the rings have the same chiralilty. ESI-MS of <b>1</b> from a methanol solution of crystals reveals the fragment [Co₁₆(L)₄­(H₃L)₈­(N₃)₆+2H]⁴⁺, suggesting the polynuclear core is stable in solution. ESI-MS measurements from the reaction solution found smaller fragments, [Co₄­(H₃L)₄–H]³⁺, [Co₄­(H₃L)₄–2H]²⁺, [Co₄­(H₃L)₄­(N₃)₂]²⁺, and [Co₂­(H₃L)₂]²⁺, and ESI-MS from a methanol solution of the solid deposit found in addition the Co₁₆ core. These results and the dependence on the synthesis time allow us to propose the process for the formation of <b>1</b>, which opens up a new way for the direct observation of the ligand-controlled assembly of clusters. In addition, the isolation of [Co₄­(H₃L)₄]­(NO₃)₄·​4H₂O (<b>2</b>) consisting of separate Co₄O₄ cubes with the ligands being only <i>cis</i> in crystalline form supports the proposal. Interestingly, N₃^ is replaced by either CH₃O^– or OH^–, and this is the first time that high-resolution ESI-MS is successfully utilized to examine both the step-by-step elimination and substitution of inner bridging ligands in such a high nuclear complex. Increasing the voltage results in stepwise elimination of azide from the parent cluster. The preliminary magnetic susceptibility of <b>1</b> indicates ferromagnetic cubes antiferromagnetically coupled to the squares within the cluster, though in a field of 2.5 kOe, weak and slow relaxation is observed below 4 K

Mn(II)-Based Porous Metal–Organic Framework Showing Metamagnetic Properties and High Hydrogen Adsorption at Low Pressure

A Mn­(II)-based homometallic porous metal–organic framework, Mn₅(btac)₄(μ₃-OH)₂(EtOH)₂·DMF·3EtOH·3H₂O (<b>1</b>, btac <b>=</b> benzotriazole-5-carboxylate), has been solvothermally synthesized and structurally characterized by elemental analysis, thermogravimetric analysis, and X-ray crystallographic study. <b>1</b> is a 3D neutral framework featuring 1D porous channels constructed by {Mn–OH–Mn}_<i>n</i> chains and btac linkers. Magnetic studies show that <b>1</b> is a 3D metamagnet containing 1D {Mn–OH–Mn}_<i>n</i> ferrimagnetic chains. High-pressure H₂ adsorption measurement at 77 K reveals that activated <b>1</b> can absorb 0.99 wt % H₂ at 0.5 atm and reaches a maximum of 1.03 wt % at 5.5 atm. The steep H₂ absorption at lower pressure (98.2% of the storage capacity at 0.5 atm) is higher than the corresponding values of some MOFs (MIL-100 (16.1%), MOF-177 (57.1%), and MOF-5 (22.2%)). Furthermore, activated <b>1</b> can adsorb CO₂ at room temperature and 275 K. The adsorption enthalpy is 22.0 kJ mol^–1, which reveals the high binding ability for CO₂. Detailed gas sorption implies that the exposed Mn­(II) coordination sites in the activated <b>1</b> play an important role to improve its adsorption capacities