Redox-Active Cobalt(II/III) Metal–Organic Framework for Selective Oxidation of Cyclohexene

We report herein a new cobalt­(II/III) mixed-valence metal–organic framework formulated as [Co^IICo₂^III(μ₃-O)­(bdc)₃(tpt)]·guest <b>1</b>, where bdc = benzene-1,4-dicarboxylate and tpt = 2,4,6-tri­(4-pyridinyl)-1,3,5-triazine, which can be used as a redox-active heterogeneous catalyst for selective oxidation of cyclohexene on the allylic position without destroying the adjacent double bond. Two oxidants were chosen to demonstrate this result. For using <i>tert</i>-butyl hydroperoxide, the conversion rate is 63% and only allylic oxidation products (<i>tert</i>-butyl-2-cyclohexenyl-1-peroxide, 86%; 2-cyclohexen-1-one, 14%) are found, whereas if using O₂ as oxidant, a total conversion of 38% is achieved and also only the allylic oxidation products (cyclohexenyl hydroperoxide, 72%; 2-cyclohexen-1-one, 20%; and cyclohex-2-en-1-ol, 8%) are found. The absence of any adduct on the double bond may be due to the unique radical chain mechanism triggered by the mixed-valent [Co^IICo₂^III(μ₃-O)] centers

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

Redox-Active Cobalt(II/III) Metal–Organic Framework for Selective Oxidation of Cyclohexene

We report herein a new cobalt­(II/III) mixed-valence metal–organic framework formulated as [Co^IICo₂^III(μ₃-O)­(bdc)₃(tpt)]·guest <b>1</b>, where bdc = benzene-1,4-dicarboxylate and tpt = 2,4,6-tri­(4-pyridinyl)-1,3,5-triazine, which can be used as a redox-active heterogeneous catalyst for selective oxidation of cyclohexene on the allylic position without destroying the adjacent double bond. Two oxidants were chosen to demonstrate this result. For using <i>tert</i>-butyl hydroperoxide, the conversion rate is 63% and only allylic oxidation products (<i>tert</i>-butyl-2-cyclohexenyl-1-peroxide, 86%; 2-cyclohexen-1-one, 14%) are found, whereas if using O₂ as oxidant, a total conversion of 38% is achieved and also only the allylic oxidation products (cyclohexenyl hydroperoxide, 72%; 2-cyclohexen-1-one, 20%; and cyclohex-2-en-1-ol, 8%) are found. The absence of any adduct on the double bond may be due to the unique radical chain mechanism triggered by the mixed-valent [Co^IICo₂^III(μ₃-O)] centers

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

Structure Tunable Organic–Inorganic Bismuth Halides for an Enhanced Two-Dimensional Lead-Free Light-Harvesting Material

Structure Tunable Organic–Inorganic Bismuth Halides for an Enhanced Two-Dimensional Lead-Free Light-Harvesting Materia

Cobalt(II) Magnetic Metal–Organic Framework with an Effective Kagomé Lattice, Large Surface Area, and High Spin-Canted Ordering Temperature

To make a porous material with high magnetic ordering temperature is challenging because the low density of the material is adverse to the dense magnetic moment, a prerequisite to high-performance magnets. Herein, we report a hollow magnetic metal–organic framework (MMOF) [Co₃(bpdc)₃(tpt)_0.66] <b>1</b> (H₂bpdc = 4,4′-biphenyldicarboxylic acid) with a Langmuir surface area of 1118 m²/g and spin-canted long-range magnetic ordering up to 22 K. Such a high performance is owing to the unique antiferromagnetic Kagomé lattice made of ferromagnetic Co₃ clusters and conjugated 2,4,6-tri­(4-pyridinyl)-1,3,5-triazine (tpt) ligands, which is closely coupled with each other via double-interpenetration of the porous networks. Moreover, a parameter defined as the product of magnetic ordering/blocking temperature and the surface area for measuring the performance of porous molecular magnets is proposed

Cobalt(II) Magnetic Metal–Organic Framework with an Effective Kagomé Lattice, Large Surface Area, and High Spin-Canted Ordering Temperature

To make a porous material with high magnetic ordering temperature is challenging because the low density of the material is adverse to the dense magnetic moment, a prerequisite to high-performance magnets. Herein, we report a hollow magnetic metal–organic framework (MMOF) [Co₃(bpdc)₃(tpt)_0.66] <b>1</b> (H₂bpdc = 4,4′-biphenyldicarboxylic acid) with a Langmuir surface area of 1118 m²/g and spin-canted long-range magnetic ordering up to 22 K. Such a high performance is owing to the unique antiferromagnetic Kagomé lattice made of ferromagnetic Co₃ clusters and conjugated 2,4,6-tri­(4-pyridinyl)-1,3,5-triazine (tpt) ligands, which is closely coupled with each other via double-interpenetration of the porous networks. Moreover, a parameter defined as the product of magnetic ordering/blocking temperature and the surface area for measuring the performance of porous molecular magnets is proposed