Insertion of Functional Groups into a Nd³⁺ Metal–Organic Framework via Single-Crystal-to-Single-Crystal Coordinating Solvent Exchange

Single-crystal-to-single-crystal (SCSC) transformations represent some of the most fascinating phenomena in chemistry. They are not only intriguing from a basic science point of view but also provide a means to modify or tune the properties of the materials via the postsynthetic introduction of suitable guest molecules or organic functional groups into their structures. Here, we describe <b>UCY-2</b>, a new flexible Nd³⁺ metal–organic framework (MOF), which exhibits a unique capability to undergo a plethora of SCSC transformations with some of them being very uncommon. These structural alterations involve the replacement of coordinating solvent molecules of <b>UCY-2</b> by terminally ligating solvents and organic ligands with multiple functional groups including −OH, −SH, −NH–, and −NH₂ or their combinations, chelating ligands, anions, and two different organic compounds. The SCSC coordinating solvent exchange is thus demonstrated as a powerful method for the functionalization of MOFs

[Mn₁₂O₁₂(OMe)₂(O₂CPh)₁₆(H₂O)₂]^2- Single-Molecule Magnets and Other Manganese Compounds from a Reductive Aggregation Procedure

A new synthetic procedure has been developed in Mn cluster chemistry involving reductive aggregation of permanganate (MnO4-) ions in MeOH in the presence of benzoic acid, and the first products from its use are described. The reductive aggregation of NBun4MnO4 in MeOH/benzoic acid gave the new 4MnIV, 8MnIII anion [Mn12O12(OMe)2(O2CPh)16(H2O)2]2-, which was isolated as a mixture of two crystal forms (NBun4)2[Mn12O12(OMe)2(O2CPh)16(H2O)2]·2H2O·4CH2Cl2 (1a) and (NBun4)2[Mn12O12(OMe)2(O2CPh)16(H2O)2]·2H2O·CH2Cl2 (1b). The anion of 1 contains a central [MnIV4(μ3-O)2(μ-O)2(μ-OMe)2]6+ unit surrounded by a nonplanar ring of eight MnIII atoms that are connected to the central Mn4 unit by eight bridging μ3-O2- ions. This compound is very similar to the well-known [Mn12O12(O2CR)16(H2O)4] complexes (hereafter called “normal Mn12”), with the main difference being the structure of the central cores. Longer reaction times (∼2 weeks) led to isolation of polymeric [Mn(OMe)(O2CPh)2]n (2), which contains a linear chain of repeating [MnIII(μ-O2CPh)2(μ-OMe)MnIII] units. The chains are parallel to each other and interact weakly through π-stacking between the benzoate rings. When KMnO4 was used instead of NBun4MnO4, two types of compounds were obtained, [Mn12O12(O2CPh)16(H2O)4] (3), a normal Mn12 complex, and [Mn4O2(O2CPh)8(MeOH)4]·2MeOH (4·2MeOH), a new member of the Mn4 butterfly family. The cyclic voltammogram of 1 exhibits three irreversible processes, two reductions and one oxidation. One-electron reduction of 1 by treatment with 1 equiv of I- in CH2Cl2 gave (NBun4)[Mn12O12(O2CPh)16(H2O)3]·6CH2Cl2 (5·6CH2Cl2), a normal Mn12 complex in a one-electron reduced state. The variable-temperature magnetic properties of 1, 2, and 5 were studied by both direct current (dc) and alternating current (ac) magnetic susceptibility measurements. Variable-temperature dc magnetic susceptibility studies revealed that (i) complex 1 possesses an S = 6 ground state, (ii) complex 2 contains antiferromagnetically coupled chains, and (iii) complex 5 is a typical [Mn12]- cluster with an S = 19/2 ground state. Variable-temperature ac susceptibility measurements suggested that 5 and both isomeric forms of 1 (1a,b) are single-molecule magnets (SMMs). This was confirmed by the observation of hysteresis loops in magnetization vs dc field scans. In addition, 1a,b, like normal Mn12 clusters, display both faster and slower relaxing magnetization dynamics that are assigned to the presence of Jahn−Teller isomerism

New Zn²⁺ Metal Organic Frameworks with Unique Network Topologies from the Combination of Trimesic Acid and Amino-Alcohols

A series of new Zn²⁺-trimesate (btc^3‑) metal organic frameworks (MOFs) has been isolated in the presence of various amino-alcohols under solvothermal conditions. Thus, the reaction of ZnCl₂ with trimesic acid (H₃btc) and the amino-alcohols triethanolamine (teoa), 2-(hydroxymethyl)­piperidine (hmpip), <i>N</i>-<i>tert</i>-butyldiethanolamine (tbdeoa), 1,4-bis­(2-hydroxyethyl)­piperazine (bhep), <i>N</i>-methyldiethanolamine (mdeoa), or 4-(2-hydroxyethyl)­morpholine (hem) in a 1.6:1:5.6 molar ratio in DMF afforded compounds (teoaH)₂[Zn­(btc)_1.33] (<b>MOAAF-1</b>) (MOAAF = metal organic amino-alcohol framework), (NH₂Me₂)₂(hmpipH)­[Zn₃(btc)₃] (<b>MOAAF-2</b>), (NH₂Me₂)­(tbdmaH)₂[Zn₃(btc)₃] (<b>MOAAF-3</b>) (tbdma = <i>N</i>-<i>tert</i>-butyl-dimethylamine), (NH₂Me₂)­(bhepH₂)­[Zn₃(btc)₃] (<b>MOAAF-4</b>), (NH₂Me₂)­[Zn₄(btc)₃(mdeoa)₂] (<b>MOAAF-5</b>), and (NH₂Me₂)­[Zn₄(btc)₃(hem)₂] (<b>MOAAF-6</b>), respectively. The compounds display 3D structures with relatively large cavities (4–10 Å) and high potential solvent-accessible areas (38–68% of the unit cell volumes). A number of novel structural features are revealed in the reported MOFs, such as unprecedented dinuclear [Zn₂(COO)₅]⁻¹ secondary building units (SBUs) and unique network topologies (e.g., in compounds <b>MOAAF-2</b>, <b>MOAAF-3</b>, <b>MOAAF-5</b>, and <b>MOAAF-6</b>). The amino-alcohols employed played a key role for the appearance of such novel structural features in <b>MOAAF 1</b>–<b>6</b> since they were found to act as bases responsible for the deprotonation of H₃btc, templates, and chelating ligands. Specifically, most of the compounds synthesized were shown to be templated by protonated amino-alcohols that are involved in hydrogen bonding interactions with the frameworks, whereas in two cases (compounds <b>MOAAF-5</b> and <b>MOAAF-6</b>) the amino-alcohols acted as chelating ligands affecting significantly the underline topology of the MOFs. The thermal stability and photoluminescence properties of the MOFs are also discussed. This work represents the initial systematic investigation on the use of combination of amino-alcohols and polycarboxylate ligands for the synthesis of new MOFs, demonstrating it as a powerful synthetic strategy for the isolation of novel MOFs

Template Synthesis and Single-Molecule Magnetism Properties of a Complex with Spin <i>S</i> = 16 and a [Mn₈O₈]⁸⁺ Saddle-Like Core

The compound [CeIVMnIII8O8(O2CMe)12(H2O)4]·4H2O (1·4H2O) has been obtained from a template synthesis involving the reaction of the chain polymer {[MnIII(OH)(O2CMe)2] ·(MeCO2H)·(H2O)}n (3) with Ce(IV). Compound 1 contains a MnIII8 loop inside which is held the Ce(IV) ion by the bridging oxide ions. Magnetization and magnetic susceptibility studies establish that 1 has an S = 16 spin ground state, the largest yet for a Mn cluster, and displays the slow magnetization relaxation and hysteresis behavior of a single-molecule magnet (SMM). It is thus the highest spin Mn SMM discovered to date

Insertion of Functional Groups into a Nd³⁺ Metal–Organic Framework via Single-Crystal-to-Single-Crystal Coordinating Solvent Exchange

Single-crystal-to-single-crystal (SCSC) transformations represent some of the most fascinating phenomena in chemistry. They are not only intriguing from a basic science point of view but also provide a means to modify or tune the properties of the materials via the postsynthetic introduction of suitable guest molecules or organic functional groups into their structures. Here, we describe <b>UCY-2</b>, a new flexible Nd³⁺ metal–organic framework (MOF), which exhibits a unique capability to undergo a plethora of SCSC transformations with some of them being very uncommon. These structural alterations involve the replacement of coordinating solvent molecules of <b>UCY-2</b> by terminally ligating solvents and organic ligands with multiple functional groups including −OH, −SH, −NH–, and −NH₂ or their combinations, chelating ligands, anions, and two different organic compounds. The SCSC coordinating solvent exchange is thus demonstrated as a powerful method for the functionalization of MOFs

High-Nuclearity Ce/Mn and Th/Mn Cluster Chemistry: Preparation of Complexes with [Ce₄Mn₁₀O₁₀(OMe)₆]¹⁸⁺ and [Th₆Mn₁₀O₂₂(OH)₂]¹⁸⁺ Cores

The syntheses, structures, and magnetic properties are reported of the mixed-metal complexes [Ce4Mn10O10(OMe)6(O2CPh)16(NO3)2(MeOH)2(H2O)2] (1) and [Th6Mn10O22(OH)2(O2CPh)16-(NO3)2(H2O)8] (2), which were both prepared by the reaction of (NBun4)[Mn4O2(O2CPh)9(H2O)] (3) with a source of the heterometal in MeCN/MeOH. Complexes 1 and 2 crystallize in the monoclinic space group C2/c and the triclinic space group P1̄, respectively. Complex 1 consists of 10 MnIII, 2 CeIII, and 2 CeIV atoms and possesses a very unusual tubular [Ce4Mn10O10(OMe)6]18+ core. Complex 2 consists of 10 MnIV and 6 ThIV atoms and possesses a [Th6Mn10O22(OH)2]18+ core with the metal atoms arranged in layers with a 2:3:6:3:2 pattern. Peripheral ligation around the cores is provided by 16 bridging benzoates, 2 chelating nitrates, and either (i) 2 each of terminal H2O and MeOH groups in 1 or (ii) 8 terminal H2O groups in 2. Complex 1 is the largest mixed-metal Ce/Mn cluster and the first 3d/4f cluster with mixed-valency in its lanthanide component, while complex 2 is the first Th/Mn cluster and the largest mixed transition metal/actinide cluster to date. Solid-state dc and ac magnetic susceptibility measurements on 1 and 2 establish that they possess S = 4 and 3 ground states, respectively. Ac susceptibility studies on 1 revealed nonzero frequency-dependent out-of-phase (χM‘ ‘) signals at temperatures below 3 K; complex 2 displays no χM‘ ‘ signals. However, single-crystal magnetization vs dc field scans at variable temperatures and variable sweep-rates down to 0.04 K on 1 revealed no noticeable hysteresis loops, except very minor ones at 0.04 K assignable to weak intermolecular interactions propagated by hydrogen bonds involving CeIII-bound ligands. Complex 1 is thus concluded not to be a single-molecule magnet (SMM), and the combined results thus represent a caveat against taking such ac signals as sufficient proof of a SMM

New Zn²⁺ Metal Organic Frameworks with Unique Network Topologies from the Combination of Trimesic Acid and Amino-Alcohols

A series of new Zn²⁺-trimesate (btc^3‑) metal organic frameworks (MOFs) has been isolated in the presence of various amino-alcohols under solvothermal conditions. Thus, the reaction of ZnCl₂ with trimesic acid (H₃btc) and the amino-alcohols triethanolamine (teoa), 2-(hydroxymethyl)­piperidine (hmpip), <i>N</i>-<i>tert</i>-butyldiethanolamine (tbdeoa), 1,4-bis­(2-hydroxyethyl)­piperazine (bhep), <i>N</i>-methyldiethanolamine (mdeoa), or 4-(2-hydroxyethyl)­morpholine (hem) in a 1.6:1:5.6 molar ratio in DMF afforded compounds (teoaH)₂[Zn­(btc)_1.33] (<b>MOAAF-1</b>) (MOAAF = metal organic amino-alcohol framework), (NH₂Me₂)₂(hmpipH)­[Zn₃(btc)₃] (<b>MOAAF-2</b>), (NH₂Me₂)­(tbdmaH)₂[Zn₃(btc)₃] (<b>MOAAF-3</b>) (tbdma = <i>N</i>-<i>tert</i>-butyl-dimethylamine), (NH₂Me₂)­(bhepH₂)­[Zn₃(btc)₃] (<b>MOAAF-4</b>), (NH₂Me₂)­[Zn₄(btc)₃(mdeoa)₂] (<b>MOAAF-5</b>), and (NH₂Me₂)­[Zn₄(btc)₃(hem)₂] (<b>MOAAF-6</b>), respectively. The compounds display 3D structures with relatively large cavities (4–10 Å) and high potential solvent-accessible areas (38–68% of the unit cell volumes). A number of novel structural features are revealed in the reported MOFs, such as unprecedented dinuclear [Zn₂(COO)₅]⁻¹ secondary building units (SBUs) and unique network topologies (e.g., in compounds <b>MOAAF-2</b>, <b>MOAAF-3</b>, <b>MOAAF-5</b>, and <b>MOAAF-6</b>). The amino-alcohols employed played a key role for the appearance of such novel structural features in <b>MOAAF 1</b>–<b>6</b> since they were found to act as bases responsible for the deprotonation of H₃btc, templates, and chelating ligands. Specifically, most of the compounds synthesized were shown to be templated by protonated amino-alcohols that are involved in hydrogen bonding interactions with the frameworks, whereas in two cases (compounds <b>MOAAF-5</b> and <b>MOAAF-6</b>) the amino-alcohols acted as chelating ligands affecting significantly the underline topology of the MOFs. The thermal stability and photoluminescence properties of the MOFs are also discussed. This work represents the initial systematic investigation on the use of combination of amino-alcohols and polycarboxylate ligands for the synthesis of new MOFs, demonstrating it as a powerful synthetic strategy for the isolation of novel MOFs

Fine Tuning the Hydrophobicity of a New Three-Dimensional Cu²⁺ MOF through Single Crystal Coordinating Ligand Exchange Transformations

The synthesis, characterization, and single–crystal–to–single–crystal (SCSC) exchange reactions of a new 3D Cu2+ MOF based on 5-aminoisophthalic acid (H2AIP), [Cu6(μ3-ΟΗ)3(ΑΙΡ)4(HΑΙΡ)]n·6nDMF·nH2O - UCY-16·6nDMF·nH2O, are reported. It exhibits a 3D structure based on two [Cu4(μ3–OH)2]6+ butterfly–like secondary building units, differing in their peripheral ligation, bridged through HAIP–/AIP2– ligands. This compound displays the capability to exchange the coordinating ligand(s) and/or guest solvent molecules through SCSC reactions. Interestingly, heterogeneous reactions of single crystals of UCY-16·6nDMF·nH2O with primary alcohols resulted not only in the removal of the lattice DMF molecules but also in an unprecedented structural alteration that involved the complete or partial replacement of the monoatomic bridging μ3–OH– anion(s) of the [Cu4(μ3–OH)2]6+ butterfly structural core by various alkoxy groups. Similar crystal-to-crystal exchange reactions of UCY-16·6nDMF·nH2O with long-chain aliphatic alcohols (CxH2x+1OH, x = 8–10, 12, 14, and 16) led to analogues containing fatty alcohols. Notably, the exchanged products with the bulkier alcohols UCY-16/n-CxH2x+1OH·S′ (x = 6–10, 12, 14, and 16) do not mix with H2O being quite stable in this solvent, in contrast to the pristine MOF, and exhibit a hydrophobic/superhydrophobic surface as confirmed from the investigation of their water contact angles and capability to remove hydrophobic pollutants from aqueous media

High-Nuclearity Ce/Mn and Th/Mn Cluster Chemistry: Preparation of Complexes with [Ce₄Mn₁₀O₁₀(OMe)₆]¹⁸⁺ and [Th₆Mn₁₀O₂₂(OH)₂]¹⁸⁺ Cores

The syntheses, structures, and magnetic properties are reported of the mixed-metal complexes [Ce4Mn10O10(OMe)6(O2CPh)16(NO3)2(MeOH)2(H2O)2] (1) and [Th6Mn10O22(OH)2(O2CPh)16-(NO3)2(H2O)8] (2), which were both prepared by the reaction of (NBun4)[Mn4O2(O2CPh)9(H2O)] (3) with a source of the heterometal in MeCN/MeOH. Complexes 1 and 2 crystallize in the monoclinic space group C2/c and the triclinic space group P1̄, respectively. Complex 1 consists of 10 MnIII, 2 CeIII, and 2 CeIV atoms and possesses a very unusual tubular [Ce4Mn10O10(OMe)6]18+ core. Complex 2 consists of 10 MnIV and 6 ThIV atoms and possesses a [Th6Mn10O22(OH)2]18+ core with the metal atoms arranged in layers with a 2:3:6:3:2 pattern. Peripheral ligation around the cores is provided by 16 bridging benzoates, 2 chelating nitrates, and either (i) 2 each of terminal H2O and MeOH groups in 1 or (ii) 8 terminal H2O groups in 2. Complex 1 is the largest mixed-metal Ce/Mn cluster and the first 3d/4f cluster with mixed-valency in its lanthanide component, while complex 2 is the first Th/Mn cluster and the largest mixed transition metal/actinide cluster to date. Solid-state dc and ac magnetic susceptibility measurements on 1 and 2 establish that they possess S = 4 and 3 ground states, respectively. Ac susceptibility studies on 1 revealed nonzero frequency-dependent out-of-phase (χM‘ ‘) signals at temperatures below 3 K; complex 2 displays no χM‘ ‘ signals. However, single-crystal magnetization vs dc field scans at variable temperatures and variable sweep-rates down to 0.04 K on 1 revealed no noticeable hysteresis loops, except very minor ones at 0.04 K assignable to weak intermolecular interactions propagated by hydrogen bonds involving CeIII-bound ligands. Complex 1 is thus concluded not to be a single-molecule magnet (SMM), and the combined results thus represent a caveat against taking such ac signals as sufficient proof of a SMM

Characterization and Magnetic Properties of a “Super Stable” Radical 1,3-Diphenyl-7-trifluoromethyl-1,4-dihydro-1,2,4-benzotriazin-4-yl

1,3-Diphenyl-7-trifluoromethyl-1,4-dihydro-1,2,4-benzotriazin-4-yl (4), prepared in high yield via the catalytic oxidation of the corresponding amidrazone 5 by using Pd/C (1.6 mol %) and 1,8-diazabicyclo[5.4.0]undec-7-ene (0.1 equiv) in air, is stable in dichloromethane solutions in the presence of MnO2 and KMnO4. Furthermore, radical 4 is thermally stable well past its melting point (160−161 °C) with a decomposition onset temperature of 288 °C. X-ray studies show that radical 4 packs in equidistant slipped π-stacks along the a axis. Cyclic voltammetry shows two fully reversible waves, corresponding to the −1/0, 0/+1 processes. EPR studies indicate that the spin density is mainly delocalized on the triazinyl fragment of the heterocycle. Magnetic susceptibility measurements in the 5−300 K region showed that the radical obeys Curie−Weiss behavior down to 10 K (C = 0.376 emu·K·mol−1 and θ = +1.41 K) consistent with weak ferromagnetic interactions between S = 1/2 radicals. Subsequent fitting of the magnetic data to a 1D ferromagnetic chain model provided an excellent fit (g = 2.00, J/k = +1.49 K) down to 10 K but failed to reproduce the subsequent decrease in χT at lower temperatures, which has been ascribed to the onset of weaker antiferromagnetic interactions between ferromagnetic chains