Synthesis and Mechanism Studies of a High-Nuclear Mn72W48 Cluster

Two SiO44--Templated Ln23Ni20 Clusters with Magnetic Cooling and Stability

Assembling and studying high-nuclearity 3d-4f metal clusters represent a pregnant and challenging research hotspot. Based on anionic template and ligand-controlled hydrolytic methods, two heterometallic metal clusters, formulated as [Gd₂₃Ni₂₀(DTA)₂₀(CO₃)₄(CH₃COO)₆(SiO₄)₄(CH₃CH₂OH)₂(μ₃-OH)₃₃(μ₂-OH)₄(H₂O)₁₆]·Cl₂·30H₂O and [Eu₂₃Ni₂₀(DTA)₂₀(CO₃)₄(CH₃COO)₆(SiO₄)₄(CH₃CH₂OH)₂(μ₃-OH)₃₃(μ₂-OH)₄(H₂O)₁₆]·Cl₂·46H₂O (abbreviated as Gd₂₃Ni₂₀, Eu₂₃Ni₂₀, H₂DTA = thiodiglycolic acid), are successfully obtained, which both feature similar double-shell-shaped structures with a Ni₂₀ building unit encapsulating a Ln₂₃ aggregation. The structural analysis illustrates that the SiO₄^4- anion, serving as the anionic template in this work, is reported for the second time in 3d-4f metal clusters. In terms of the magnetic properties, large amounts of Gd³⁺ and Ni²⁺ ions contribute to the MCE of compound Gd₂₃Ni₂₀, along with 38.15 J kg^-1 K^-1 at ΔH = 7.0 T for 2.0 K. It is worth mentioning that compound Gd₂₃Ni₂₀ exhibits an excellent magnetic entropy change at low fields (-ΔS_m = 19.10 J kg^-1 K^-1 at 2.0 K for ΔH = 2.0 T). In addition, Gd₂₃Ni₂₀ exhibits preferable solvent and thermal stability.

Template-Induced {Mn2}-Organic Framework with Lewis Acid-Base Canals as a Highly Efficient Heterogeneous Catalyst for Chemical Fixation of CO2 and Knoevenagel Condensation

The target for the self-assembly of functional microporous metal-organic frameworks (MOFs) could be realized by employing ligand-directed and/or template-induced strategies, which prompted us to explore the synthetic technique of d¹⁰ secondary-building-unit-based nanoporous frameworks. Here, the exquisite combination of a paddle-wheel [Mn₂(CO₂)₆(OH₂)₂] cluster and a TDP^6- ligand contributes one robust honeycomb framework of {(Me₂NH₂)₂[Mn₂(TDP)(H₂O)₂]·3H₂O·3DMF}_n (NUC-31; DMF = N,N-dimethylformamide), whose activated state with the removal of associated aqueous molecules characterizes the outstanding physicochemical properties of nanochannels, penta- and tetracoordinated Mn²⁺ serving as highly open metal sites, rich Lewis base sites (rows of C═O groups and N_pyridine atoms), and excellent thermal stability. Moreover, it is worth mentioning that Lewis acid-base sites on the inner surface of the channels in activated NUC-31 successfully form one unprecedented canal-shaped acid-base confined space with evenly distributed open metal sites of Mn²⁺ and N_pyridine atoms as the canal bottom as well as two rows of C═O groups serving as dyke dams. Catalytic experiments displayed that activated NUC-31 could serve as an efficient heterogeneous catalyst for the chemical fixation of CO₂ with epoxides into cyclic carbonates under mild conditions. Furthermore, NUC-31 could effectively catalyze the reaction Knoevenagel condensation, which should be ascribed to the synergistic polarization effect aroused from its plentiful Lewis base sites in the confined channel space. Hence, these results demonstrate that the employment of ligand-directed and template-dependent strategies could overcome the self-assembled barriers of functional microporous MOFs and achieve unexpected frameworks.

V═O Functionalized {Tm2}-Organic Framework Designed by Postsynthesis Modification for Catalytic Chemical Fixation of CO2 and Oxidation of Mustard Gas

In terms of recently documented references, the introduction of V═O units into porous MOF/COF frameworks can greatly improve their original performance and expand their application prospects due to a change in their electronegativity. In this work, by a cation-exchange strategy, a consummate combination of separate 4f [Tm₂(CO₂)₈] SBUs and 3d [V^IVO(H₂O)₂] units generated the functionalized porous metal-organic framework {(Me₂NH₂)₂[VO(H₂O)][Tm₂(BDCP)₂]·3DMF·3H₂O}_n (NUC-11), in which [Tm₂(CO₂)₈] SBUs constitute the fundamental 3D host framework of {[Tm₂](BDCP)₂}_n along with [V^IVO(H₂O)₂] units being further docked on the inner wall of channels by covalent bonds. Significantly, NUC-11 represents the first example of V═O modified porous MOFs, in which uncoordinated carboxylic groups (-CO₂H) further grasp the functional [V^IVO(H₂O)₂] units on the initial basic skeleton along with the formation of covalent bonds as fixed ropes. Furthermore, activated samples of NUC-11 displayed a good catalytic performance for the chemical synthesis of carbonates from related epoxides and CO₂ with high conversion rate. Moreover, by employing NUC-11 as a catalyst, a simulator of mustard gas, 2-chloroethyl ethyl sulfide, could be quickly and efficiently oxidized into low-toxicity products of oxidized sulfoxide (CEESO). Thus, this study offers a brand new view for the design and synthesis of functional-units-modified porous MOFs, which could be potentially applied as an excellent candidate in the growing field of efficient catalysis.

Nanochannel-based heterometallic {ZnIIHoIII}-organic framework with high catalytic activity for the chemical fixation of CO2

The exquisite combination of ZnII and HoIII generated the highly robust [ZnHo(CO2)6(OH2)]-based heterometallic framework of {[ZnHo(TDP)(H2O)]·5H2O·3DMF} n (NUC-30, H6TDP = 2,4,6-tri(2',4'-dicarboxyphenyl)pyridine), which featured outstanding physicochemical properties, including honeycomb nanochannels, high porosity, large specific surface area, the coexistence of highly open Lewis acid-base sites, good thermal and chemical stability, and resistance to most organic solvents. Due to its extremely unsaturated metal tetra-coordinated Zn(ii) ions, hepta-coordinated Ho(iii) and high faveolate void volume (61.3%), the conversion rate of styrene oxide and CO2 into cyclic carbonates in the presence of 2 mol% activated NUC-30 and 5 mol% n-Bu4NBr reached 99% under the mild conditions of 1.0 MPa and 60 °C. Furthermore, the luminescence sensing experiments proved that NUC-30 could be used as a fast, sensitive and highly efficiency sensor for the detection of Fe3+ in aqueous solution. Therefore, these results prove that nanoporous MOFs assembled from pyridine-containing polycarboxylate ligands have wide applications, such as catalysis and as luminescent materials.

One Robust Microporous TmIII-Organic Framework for Highly Catalytic Activity on Chemical CO2 Fixation and Knoevenagel Condensation

In terms of documented references, multifunctional MOFs with high catalytic performance could be constructed from the combination of metal cations and polycarboxyl-pyridine ligands, which could efficiently endow crystallized porous frameworks with the coexisting Lewis acid-base properties. Thus, by employing a ligand-directed synthetic strategy, the exquisite combination of wave-like inorganic chains of [Tm(CO₂)₃(OH₂)]_n and mononuclear units of [Tm(CO₂)₄(OH₂)₂] with the aid of the specially designed ligand of 2,6-bis(2,4-dicarboxylphenyl)-4-(4-carboxylphenyl)pyridine (H₅BDCP) generates one highly robust microporous framework of {(Me₂NH₂)[Tm₃(BDCP)₂)(H₂O)₃]·4DMF·H₂O}_n (simplified as NUC-25), which contains near-rectangular nanochannels and large solvent-residing voids. Furthermore, the activated state of NUC-25 with the removal of associated water molecules is a rarely reported bifunctional heterogeneous catalyst due to the coexistence of Lewis acid-base sites including 6-coordinated Tm³⁺ ions, uncoordinated carboxyl oxygen atoms, and N_pyridine atoms. Just as expected, NUC-25 exhibits greatly high catalytic activity for the cycloaddition reaction of epoxides with CO₂ into alkyl cyclic carbonates under bland solvent-free conditions, which should be ascribed to the polarity of nitrogen-containing pyridine heterocycles as Lewis base sites on the inner surface of nano-caged voids except for recognized Lewis acid sites of rare earth cations. Moreover, the excellent pore-size-dependent catalytic property for Knoevenagel condensation reactions confirms that NUC-25 can be viewed as a recyclable bifunctional heterogeneous catalyst. Therefore, these results strongly demonstrate that microporous MOFs assembled from pre-designed polycarboxyl-heterocyclic ligands display better catalytic performance not only for chemical CO₂ fixation but also for Knoevenagel condensation reactions.