Double Cation−π Directed Two-Dimensional Metallacycle-Based Hierarchical Self-Assemblies for Dual-Mode Catalysis

Hierarchical self-assembly of Pt­(II) metallacycles for the construction of functional materials has received considerable research interest, owing to their potential to meet increasing complexity and functionality demands while being based on well-defined scaffolds. However, the fabrication of long-range-ordered Pt­(II) metallacycle-based two-dimensional hierarchical self-assemblies (2D HSAs) remains a challenge, primarily because of the limitations of conventional orthogonal noncovalent interaction (NCI) motifs and the intrinsic characteristics of Pt­(II) metallacycles, making the delicate self-assembly processes difficult to control. Herein, we prepare well-regulated Pt­(II)-metallacycle-based 2D HSAs through a directed strategy involving double cation−π interactions derived from C3-symmetric hexagonal Pt­(II) metallacycles and C2-symmetric sodium phenate monomers. Spatially confined arrays of planar Pt­(II) metallacycles and the selective growth of self-assemblies at desired locations are achieved by employing strong cation−π driving forces with well-defined directionality as the second orthogonal NCI, realizing the bottom-up, three-stage construction of Pt­(II)-metallacycle-based 2D HSAs. The resultant 2D HSAs are applied as dual-mode catalysis platforms, which are loaded with two different nanocatalysts, one promoting catalytic oxidation and the other promoting photocatalytic reduction

Self-Assembly of a CsCl-like 3D Supramolecular Network from [Zn₆(HL)₆(H₂L)₆]⁶⁺ Metallamacrocycles and (H₂O)₂₀ Clusters (H₂L = 4-(2-Pyridyl)-6-(4-pyridyl)-2-aminopyrimidine)

The reaction of Zn(NO3)2·6H2O with multifunctional ligand 4-(2-pyridyl)-6-(4-pyridyl)-2-aminopyrimidine (H2L) leads to a circular hexanuclear zinc complex [Zn6(HL)6(H2L)6](NO3)6·26H2O (1), confirmed by single-crystal X-ray diffraction. In the [Zn6(HL)6(H2L)6]6+ cation, six zinc centers are arranged in a chairlike conformation and 12 ligands fulfill bridging and terminal functions, respectively. The particular interest of complex 1 is the formation of a unique water cluster (H2O)26 composed of a clathrate (H2O)20 core and six dangling water molecules, and the clathrate (H2O)20 core is structurally similar to the famous “Bucky water” (H2O)20. Furthermore, the water molecules and the nitrate ions are assembled into an interesting negative three-dimensional (3D) framework through hydrogen bonds, and the [Zn6(HL)6(H2L)6]6+ cations just locate in the cavities of the anionic 3D network. To gain insight into the stability of (H2O)20 observed in complex 1, we isolate the water cluster from its environments and compare its stability with “Bucky water” (H2O)20 by a theoretical calculation method. Complex 1 displays room temperature photoluminescence

Hexaniobate as a Recyclable Solid Base Catalyst to Activate C–H Bonds in Lignin Linkage Boosting the Production of Aromatic Monomers

The targeting cleavage of lignin into value-added aromatic monomers has attracted increasing attention. Although the base-catalyzed depolymerization of lignin has been developed, the use of excess corrosive bases and their poor recyclability limit their industrial implementation. Herein, a catalytic amount of solid base K7HNb6O19 (KNb6) coupled with copper-modified graphitic carbon nitride (Cu/C3N4) shows enhanced catalytic performance for the oxidative cleavage of β-O-4 lignin linkages using molecular oxygen. Due to the synergetic effect between KNb6 and Cu/C3N4, 96% of the β-O-4 ketone model was converted under relatively mild conditions, and phenol (yield: 90%) and other aromatic monomers (yield: 90%) were obtained. Moreover, KNb6–Cu/C3N4 is robust, and its catalytic activity is basically maintained after five cycles. Experimental and theoretical studies (spectroscopic analysis, control experiments, kinetic study, density functional theory calculations, etc.) reveal that the surface basic O atoms of KNb6 can simultaneously activate the Cβ–H bond of β-O-4 ketone to promote the insertion of molecular oxygen, and subsequently, Cu/C3N4 catalyzes the selective cleavage of the Cα–Cβ bond. The catalysts were also active for the oxidative cleavages of other lignin models and oxidized organosolv lignin

Self-Assembly of a CsCl-like 3D Supramolecular Network from [Zn₆(HL)₆(H₂L)₆]⁶⁺ Metallamacrocycles and (H₂O)₂₀ Clusters (H₂L = 4-(2-Pyridyl)-6-(4-pyridyl)-2-aminopyrimidine)

The reaction of Zn(NO3)2·6H2O with multifunctional ligand 4-(2-pyridyl)-6-(4-pyridyl)-2-aminopyrimidine (H2L) leads to a circular hexanuclear zinc complex [Zn6(HL)6(H2L)6](NO3)6·26H2O (1), confirmed by single-crystal X-ray diffraction. In the [Zn6(HL)6(H2L)6]6+ cation, six zinc centers are arranged in a chairlike conformation and 12 ligands fulfill bridging and terminal functions, respectively. The particular interest of complex 1 is the formation of a unique water cluster (H2O)26 composed of a clathrate (H2O)20 core and six dangling water molecules, and the clathrate (H2O)20 core is structurally similar to the famous “Bucky water” (H2O)20. Furthermore, the water molecules and the nitrate ions are assembled into an interesting negative three-dimensional (3D) framework through hydrogen bonds, and the [Zn6(HL)6(H2L)6]6+ cations just locate in the cavities of the anionic 3D network. To gain insight into the stability of (H2O)20 observed in complex 1, we isolate the water cluster from its environments and compare its stability with “Bucky water” (H2O)20 by a theoretical calculation method. Complex 1 displays room temperature photoluminescence

Controllable Assembly of Vanadium-Containing Polyoxoniobate-Based Three-Dimensional Organic–Inorganic Hybrid Compounds and Their Photocatalytic Properties

The controllable synthesis of two vanadium-containing polyoxoniobate-based three-dimensional organic–inorganic hybrid compounds, [Co­(pn)₂]₄[HPNb₁₀V^IV₂O₄₀(V^IVO)₄]·17H₂O (<b>1</b>) and [Co­(pn)₂]₅[PNb₁₂O₄₀(V^IVO)₆]­(OH)₇·15H₂O (<b>2</b>), where pn = 1,2-diaminopropane, is realized by changing the hydrothermal temperature or adding <i>N</i>-(aminoethyl)­piperazine as an additive. Both compounds <b>1</b> and <b>2</b> are structurally characterized by single-crystal/powder X-ray diffraction and IR and X-ray photoelectron spectroscopy. Compound <b>1</b> features a new divanadium-substituted Keggin polyoxoniobate capped by four vanadyl groups, and the polyanion in <b>2</b> exhibits the highest coordination number (10-connected) in polyoxoniobate chemistry. Moreover, the photocatalytic activities of <b>1</b> and <b>2</b> for hydrogen evolution are preliminarily assessed

Synthesis and Pharmacokinetic Study of Three Gemfibrozil Salts: An Exploration of the Structure–Property Relationship

Three salts, [H₃N­(CH₂)₂NH₃)]­[gem]₂ (<b>1</b>), [H₃N­(CH₂)₃NH₃)]­[gem]₂·2H₂O (<b>2</b>), and [H₃N­(CH₂)₄NH₃)]­[gem]₂­·2H₂O (<b>3</b>) of the minimally soluble drug gmfibrozil (Hgem), used for the treatment of hyperlipidemia have been synthesized by using a series of diamine with different carbon chain lengths and characterized by single crystal/powder X-ray diffraction, Fourier transform infrared spectroscopy, and ¹H nuclear magnetic resonance. In the three salts, two protons of two gmfibrozil molecules transfer to one diamine, and the resulting organic diammonium cation and gmfibrozil anion are assembled by hydrogen bond interactions into a two-dimensional layer. Although the apparent solubility of salts <b>1</b>–<b>3</b> is obviously improved compared to that of the original gemfibrozil, pharmacokinetic studies in rats indicate the enhancement of absorption is limited with the relative bioavailability of 104% for <b>1</b>, 154% for <b>2</b>, and 108% for <b>3</b>. It is notable that the rapid dissolution behavior of salt <b>1</b>–<b>3</b> leads to the increase of maximal plasma concentration (<i>C</i>_max) and the dramatic shortening of the time required to reach the <i>C</i>_max. The investigation of the structure–property relationship shows that there is little correlation of solubility with the carbon chain length of cation which is different from previous observations, and we speculate that both electrostatic attraction and hydrogen bond interaction contribute to the solubility order (<b>2</b> > <b>1</b> > <b>3</b>)

Structural Diversity of Diosgenin Hydrates: Effect of Initial Concentration, Water Volume Fraction, and Solvent on Crystallization

Four hemihydrates (HH-I, HH-II, HH-III, and HH-IV) and two monohydrates (MH-I, MH-II) of diosgenin, a steroid sapogenin, have been prepared. Hydrates HH-I, HH-III, HH-IV, MH-I, and MH-II have been thoroughly characterized by single-crystal X-ray diffraction, powder X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetry, and differential scanning calorimetry. Although in these cases diosgenin has a similar conformation, hydrogen bonding interactions connect diosgenin and the lattice water molecule into different supermolecular structures. More importantly, three controlling factors, including initial concentration, water volume fraction, and solvent, have been investigated in the crystallization of diosgenin hydrates. The control experiments in ethanol display that as the initial concentration increases, HH-III, HH-I, and HH-II appear in order, and with the increase of water content, HH-I, HH-III, MH-I, and MH-II are obtained correspondingly. When acetone is used as solvent, HH-IV was synthesized. Moreover, we observed that stick-like crystals of HH-III gradually transform to plate-like ones of MH-I in solution at ambient conditions. This transformation is prevented by lowering temperature and is accelerated by adding water

Sodium Salts and Solvate of Rebamipide: Synthesis, Structure, and Pharmacokinetic Study

Two sodium salts (Na­(CH₃CH₂OH) (HReb) (<b>1</b>) and Na₂(H₂O)₄(Reb) (<b>2</b>)), one methanol solvate (H₂Reb·CH₃OH (<b>3</b>)), and one methyl ester (<b>4</b>) of the minimally soluble drug, rebamipide (H₂Reb), used for the treatment of gastric ulcers and gastritis have been synthesized. For the first time the structure of rebamipide has been determined by single crystal X-ray diffraction. Although salts <b>1</b> and <b>2</b> were prepared under the similar conditions, their structures are different. In <b>1</b>, rebamipide loses the proton of the carboxyl group to interact with the sodium ion, but in <b>2</b> the drug molecule converts to its prototropic tautomer and then simultaneously loses the protons of the carboxyl and hydroxyl groups to form salt. Control experiments show that reaction temperature is the key factor influencing the formation of salts. Although all methanol was used in the synthesis of <b>3</b> and <b>4</b>, in <b>3</b> methanol acts as solvent involved in the lattice, while in <b>4</b> it reacts with rebamipide to form ester. By analyzing the mass spectra of the reaction solution, we speculate that the crystallization of <b>3</b> and <b>4</b> is controlled by the product’s solubility. Dissolution studies indicate that both the maximum solubility and dissolution rate of <b>1</b>–<b>4</b> in simulated succus gastricus are improved. Furthermore, pharmacokinetic behavior of compounds <b>1</b>–<b>4</b> was investigated in rats and the results indicate that the bioavailability of <b>1</b>, <b>3</b>, and <b>4</b> upon oral administration is enhanced compared to that of API

Three Candesartan Salts with Enhanced Oral Bioavailability

Three new salts, [H₃N­(CH₂)₂NH₃]­[can]·2H₂O (<b>1</b>), [H₃N­(CH₂)₃NH₃]­[can]·2H₂O (<b>2</b>), and [NH₄]­[Hcan] (<b>3</b>), of the minimally soluble antihypertensive drug, Candesartan (H₂can), have been prepared by solvent-assisted grinding. Salts <b>1–3</b> also have been thoroughly characterized by single-crystal X-ray diffraction, powder X-ray diffraction, Fourier transform infrared spectroscopy, ¹H nuclear magnetic resonance, thermogravimetry, and differential scanning calorimetry. In the case of <b>1</b> and <b>2</b>, two protons of carboxyl and tetrazole groups of Candesartan transfer to the diamine, resulting in salts where both hydrogen bonding and electrostatic interactions that link the Candesartan and diamine (diammonium) units into a one-dimensional supramolecular ribbon. However, unlike the case in <b>1</b> and <b>2</b>, only one proton from the carboxyl group of Candesartan transfers to ammonia in <b>3</b> and ionic components now assemble into a three-dimensional supramolecular network. Dissolution studies indicate that both the apparent solubility and dissolution rate of salts <b>2</b> and <b>3</b> in phosphate buffer are dramatically improved compared to those of the original active pharmaceutical ingredient (API). Furthermore, to evaluate the absorption effect of salts <b>1–3</b> <i>in vivo</i>, pharmacokinetic studies were performed in rats. It is notable that the oral bioavailability of salts <b>1–3</b> is enhanced by 1.3, 2.5, and 3.1 times, respectively, compared to that of the API

Cu-based Polyoxometalate Catalyst for Efficient Catalytic Hydrogen Evolution

Copper-based complexes have been largely neglected as potential water reduction catalysts. This article reports the synthesis and characterization of a tetra-copper-containing polyoxotungstate, Na3K7[Cu4(H2O)2­(B-α-PW9O34)2]·30H2O (Na3K7-Cu4P2). Cu4P2 is a water-compatible catalyst for efficient visible-light-driven hydrogen evolution when coupled to (4,4′-di-tert-butyl-2,2′-dipyridyl)-bis­(2-phenylpyridine­(1H))-iridium­(III) hexafluorophosphate ([Ir­(ppy)2(dtbbpy)]­[PF6]) as a light absorber and triethanolamine (TEOA) as sacrificial electron donor. Under minimally optimized conditions, a turnover number (TON) of ∼1270 per Cu4P2 catalyst is obtained after 5 h of irradiation (light-emitting diode; λ = 455 nm; 20 mW); a photochemical quantum efficiency of as high as 15.9% is achieved. Both oxidative and reductive quenching pathways are observed by measuring the luminescence intensity of excited state [Ir­(ppy)2(dtbbpy)]+* in the presence of Cu4P2 or TEOA, respectively. Many stability studies (e.g., UV–vis absorption, FT-IR, dynamic light scattering, transmission electron microscopy, and scanning electron microscopy/energy-dispersive X-ray spectroscopy) show that catalyst Cu4P2 undergoes slow decomposition under turnover conditions; however, both the starting Cu4P2 as well as its molecular decomposition products are the dominant catalytically active species for H2 evolution not Cu or CuOx particles. Considering the high abundance and low cost of copper, the present work provides considerations for the design and synthesis of efficient, molecular, water-compatible Cu-based water reduction catalysts