Chunlin Lv

Polyoxometalatocyclophanes: Controlled Assembly of Polyoxometalate-Based Chiral Metallamacrocycles from Achiral Building Blocks

The first polyoxometalatocyclophanes have been synthesized by the covalent linkage of a hexamolybdate cluster and bisarylimido ligands containing flexible chains. These metallamacrocycles are chiral, and some of them can undergo spontaneous resolution. The work provides a new protocol for preparing chiral polyoxometalates (POMs) and chiral metallamacrocycles from achiral building blocks by fastening both ends of a flexible chain onto an achiral POM to remove the symmetric center and mirror.

χ‐Octamolybdate [MoV4MoVI4O24]4−: An Unusual Small Polyoxometalate in Partially Reduced Form from Nonaqueous Solvent Reduction

The first mixed-valent octamolybdate anion [Mo(V)(4)Mo(VI)(4)O(24)](4-), termed χ-octamolybdate due to its shape, was obtained by partial reduction of α-(Bu(4)N)(4)-[Mo(8)O(26)] in dry acetonitrile. Single-crystal X-ray structure analysis revealed that the anion includes an unusual Mo(V)(4)O(8) cubane-like cluster core, whose four side faces are capped by four MoO(4) units to form a crosslike cluster. X-ray photoelectron spectroscopy (XPS) and bond valence sum (BVS) calculations were carried out to validate the presence of mixed-valent Mo centers.

From 0D dimer to 2D Network—Supramolecular Assembly of Organic Derivatized Polyoxometalates with Remote Hydroxyl via Hydrogen Bonding

A series of remote hydroxyl functionalized organoimido derivatives of hexamolybdate, (Bu(4)N)(2)[Mo(6)O(18)(Cres)] (1) (Cres = 4-amino-m-cresol), (Bu(4)N)(2)[Mo(6)O(17)(Cres)(2)] x H(2)O (2), (Bu(4)N)(2)[Mo(6)O(18)(Phen)] x i-PrOH (Phen = p-aminophenol)(3), (Bu(4)N)(2)[Mo(6)O(18)(Phen)] x EtOH (4), (Bu(4)N)(2)[Mo(6)O(17)(Phen)(2)] (5), (Bu(4)N)(2)[Mo(6)O(18)(Naph)] (Naph = 5-amino-1-napheynyl) (6), and (Bu(4)N)(2)[Mo(6)O(18)(Chex)] x 1.5 H(2)O (Chex = trans-4-aminocyclohexanol) (7) were synthesized and characterized by single crystal X-ray diffraction, FT-IR spectra, UV-vis spectra, elemental analysis, (1)H NMR, and cyclic voltammetry. X-ray structural study reveals that intermolecular and intramolecular hydrogen bonding plays an important role in their supramolecular assembly; it is found that (i) bridged oxo ligands of hexamolybdate cluster are more inclined to form hydrogen bonds as acceptors than terminal oxo ligands in this system; (ii) small solvent molecules with hydrogen bonding donor and acceptor, such as water, i-PrOH, and EtOH, usually act as hydrogen bonding bridge in their supramolecular assembly; (iii) hydrogen bonding has an important influence on their anion conformation besides cell packing; (iv) the hydrogen bonding supramolecular assembly of compounds 1-7 demonstrate an interesting change from dimer (3), to 1D infinite single chain (4), to 1D infinite double chain (2), and to 2D network (1, 5, 6, and 7) owing to the alteration of the grafting organic ligand, the substituted number, and the crystallized solvent molecule. To explore their potential application in conductivity, the optical band gap of compounds 1-7 were determined upon their solid state reflectance spectra. Our current study not only surveys systematically hydrogen bonding interaction and supramolecular assembly of remote hydroxyl functionalized organoimido-derivatized hexamolybdates but also provides some available precursors for further modification including esterification.

Organoimido-Derivatized Hexamolybdates with a Remote Carboxyl Group: Syntheses and Structural Characterizations

Four novel organoimido derivatives of hexamolybdate containing a remote carboxyl group have been synthesized: [Bu4N]2[Mo6O18(N-C6H4-3-COOH)] (1), [Bu4N]2[Mo6O18(N-C6H4-2-CH3-4-COOH)] (2), [Bu4N]2[Mo6O18(N-C6H4-2-CH3-5-COOH)] (3), and [Bu4N]2[Mo6O18(N-C6H4-2-CH3-3-COOH)] (4) with 3-aminobenzoic acid, 4-amino-3-methylbenzoic acid, 3-amino-4-methylbenzoic acid, and 3-amino-2-methylbenzoic acid as the imido-releasing agents, respectively. Their structures have been characterized by IR, UV-vis, (1)H NMR, ESI-MS, and single-crystal X-ray diffraction techniques. Hydrogen bonding interactions play an important role in the supramolecular assemblies of these compounds in the solid state. Although the incorporated organic ligands are similar to each other, their supramolecular assembly behaviors are quite different. For compound 1, the dimer structure is formed via hydrogen bonding between the carboxyl group and the POM cluster of two neighboring cluster anions. For compound 2, the 1D chain structure is formed via hydrogen bonding between the carboxyl groups and the POM clusters of the cluster anions. For compound 3, the 2D plane structure is formed via two types of hydrogen bonding between the aromatic rings and the POM clusters of the cluster anions. For compound 4, the 1D plus 2D structures are formed via three types of hydrogen bonding between the aromatic rings and the POM clusters of the two types of cluster anions with different orientations.

Theoretical investigation of the mechanism of primary amines reacting with hexamolybdate: an insight into the organoimido functionalization and related reactions of polyoxometalates.

The functionalization of polyoxometalates (POMs), especially with an amino group to yield organonitrogenous derivatives of POMs, is an efficient approach to the enrichment of their structures and the diversification of their properties for various applications. The mechanism for the formation of organonitrogenous-derivatized hexamolybdates was explored by investigating the monofunctionalization of the [Mo(6)O(19)](2-) ion with methylamine using the density functional theory (DFT) method. The calculations show that the direct imidoylization of hexamolybdate with methylamine is both kinetically and thermodynamically unfavorable. However, this imidoylization was found to take place readily in the presence of dimethylcarbodiimide (DMC), for which the free-energy barrier was calculated to be +32.5 kcal mol(-1) in acetonitrile. Moreover, various factors controlling the efficiency of the imidoylization were examined. The calculations show that [W(5)MoO(19)](2-) has a relatively lower reactivity than [Mo(6)O(19)](2-), and that the imidoylization of [W(6)O(19)](2-) is an unfavorable process. With respect to the effect of carbodiimides, it is found that the catalytic activity is directly proportional to the electron-withdrawing effects of the substituents. As to the reactivity of R-NH(2) , the computation results indicate that the free-energy barriers of the substitution reactions are linearly correlated with the basicity constants (pK(b)) of the amino groups. It is noteworthy that the introduction of the proton dramatically decreases the free-energy barrier of the imidoylization of [Mo(6)O(19)](2-) catalyzed by DMC to 24.3 kcal mol(-1) in acetonitrile.

Pd3 cluster catalysis: Compelling evidence from in operando spectroscopic, kinetic, and density functional theory studies

Identification of metal cluster catalysis is a topic that is being investigated since a long time. Here, we report a Pd3 metal cluster catalytic reaction investigated by means of operando studies. We discovered that atomically defined tri-nuclear palladium (Pd3) is a surprisingly active catalyst for the cycloisomerization of 2-phenylethynylaniline. Operando 1H NMR spectroscopy and X-ray extended absorption fine structure (EXAFS) measurements have indicated that the structural integrity of such a catalyst remains intact throughout the reaction, which has also been confirmed by an ex situ X-ray photoelectron spectroscopy (XPS) study and catalyst recycling experiments. Kinetic data derived from operando IR spectroscopy measurements have shown that Pd3 is the active catalytic species. Density functional theory calculations have revealed a reaction pathway consistent with the kinetic data, further supported by NMR titration and X-ray crystal structure studies. Overall, the present study presents a clear example of metal cluster catalysis.

Rational Control of the Selectivity of a Ruthenium Catalyst for Hydrogenation of 4‐Nitrostyrene by Strain Regulation

Tuning the selectivity of metal catalysts is of paramount importance yet a great challenge. A new strategy to effectively control the selectivity of metal catalysts, by tuning the lattice strain, is reported. A certain amount of Co atoms is introduced into Ru catalysts to compress the Ru lattice, as confirmed by aberration-corrected high-resolution transmission electron microscopy (HRTEM) and X-ray absorption fine structure (XAFS) measurements. We discover that the lattice strain of Ru catalysts can greatly affect their selectivity, and Ru with 3 % lattice compression exhibits extremely high catalytic selectivity for hydrogenation of 4-nitrostyrene to 4-aminostyrene compared to pristine Ru (99 % vs. 66 %). Theoretical studies confirm that the optimized lateral compressive strain facilitates hydrogenation of the nitro group but impedes the hydrogenation of the vinyl group. This study provides a new guideline for designing metal catalysts with high selectivity.

Reversible proton-switchable fluorescence controlled by conjugation effect in an organically-functionalized polyoxometalate.

A novel monosubstituted organoimido hexamolybdate containing 6-nitroquinoline moiety has been successfully synthesized. This organically-functionalized polyoxometalate exhibits proton-induced switchable fluorescence property in aqueous acetonitrile solution at room temperature. Experimental and theoretical investigations of this reversible “on” and “off” switching mechanism have been carried out, and it is found that the protonation and deprotonation at the heterocyclic nitrogen atom within quinoline fragment leads to the breaking and reformation of the conjugation through strong d-π interaction between the hexamolybdate anionic cluster and the quinoline moiety, resulting in “on” and “off” luminescence signal.

Injectable nanohydroxyapatite-chitosan-gelatin micro-scaffolds induce regeneration of knee subchondral bone lesions

Subchondral bone has been identified as an attractive target for KOA. To determine whether a minimally invasive micro-scaffolds could be used to induce regeneration of knee subchondral bone lesions, and to examine the protective effect of subchondral bone regeneration on upper cartilage, a ready-to-use injectable treatment with nanohydroxyapatite-chitosan-gelatin micro-scaffolds (HaCGMs) is proposed. Human-infrapatellar-fat-pad-derived adipose stem cells (IPFP-ASCs) were used as a cellular model to examine the osteo-inductivity and biocompatibility of HaCGMs, which were feasibly obtained with potency for multi-potential differentiations. Furthermore, a subchondral bone lesion model was developed to mimic the necrotic region removing performed by surgeons before sequestrectomy. HaCGMs were injected into the model to induce regeneration of subchondral bone. HaCGMs exhibited desirable swelling ratios, porosity, stiffness, and bioactivity and allowed cellular infiltration. Eight weeks after treatment, assessment via X-ray imaging, micro-CT imaging, and histological analysis revealed that rabbits treated with HaCGMs had better subchondral bone regeneration than those not treated. Interestingly, rabbits in the HaCGM treatment group also exhibited improved reservation of upper cartilage compared to those in other groups, as shown by safranin O-fast green staining. Present study provides an in-depth demonstration of injectable HaCGM-based regenerative therapy, which may provide an attractive alternative strategy for treating KOA.