Structures and photocatalytic properties of two new Zn(ii) coordination polymers based on semi-rigid V-shaped multicarboxylate ligands

Two new metal–organic coordination polymers (CPs), aqua-2,2′-bipyridine-5-(4′-carboxylphenoxy)isophthalatezinc(ii) polymer [Zn(HL)(2,2′-bipy)(H₂O)]_n (1) and tris-4,4′-bipyridine-bis-5-(4′-carboxylphenoxy)isophthalatetrizinc(ii) polymer [Zn₃(L)2(4,4′-bipy)₃]_n (2) (H₃L = 5-(4′-carboxylphenoxy)isophthalic acid, 4,4′-bipy = 4,4′-bipyridine and 2,2′-bipy = 2,2′-bipyridine), were obtained under hydrothermal conditions and characterized by microanalysis, FTIR spectroscopy and single crystal X-ray diffraction. The single crystal X-ray diffraction indicated that in both the CPs the coordination networks exhibited varied topologies and coordination modes around the Zn(ii) centers. CP 1 exhibits a one-dimensional (1D) chain structure, which further forms a 3D supramolecular architecture via intermolecular π⋯π and hydrogen bonding interactions, while 2 possesses a 3D framework generated from a 2D layered motif comprising zinc and tripodal carboxylate subunits pillared by 4,4′-bpy ligands. Apart from the structural investigation, the photocatalytic performances of both the coordination polymers to photodecompose an aqueous solution of methyl violet (MV) were examined. The results indicated that both the CPs displayed the potential to photodecompose aromatic dyes and in particular 2 showed good photocatalytic activity for dye degradation under light irradiation. The photocatalytic mechanism through which these CPs executed degradation of dyes has been explained with the assistance of band gap calculations using density of states (DOS) and its decomposed partial DOS calculations.

Two new Zn(ii) coordination polymers having semi-rigid V-shaped polycarboxylate ligands were synthesized and their photocatalytic performances to photodegrade methyl violet were assessed.     

Heterogeneous water oxidation photocatalysis based on periodic mesoporous organosilica immobilizing a tris(2,2′-bipyridine)ruthenium sensitizer

A periodic mesoporous organosilica (PMO) containing 2,2′-bipyridine groups (BPy-PMO) has been shown to possess a unique pore wall structure in which the 2,2′-bipyridine groups are densely and regularly packed. The surface 2,2′-bipyridine groups can function as chelating ligands for the formation of metal complexes, thus generating molecularly-defined catalytic sites that are exposed on the surface of the material. We here report the construction of a heterogeneous water oxidation photocatalyst by immobilizing several types of tris(2,2′-bipyridine)ruthenium complexes on BPy-PMO where they function as photosensitizers in conjunction with iridium oxide as a catalyst. The Ru complexes produced on BPy-PMO in this work were composed of three bipyridine ligands, including the BPy in the PMO framework and two X₂bpy, denoted herein as Ru(X)-BPy-PMO where X is H (2,2′-bipyridine), Me (4,4′-dimethyl-2,2′-bipyridine), t-Bu(4,4′-di-tert-butyl-2,2′-bipyridine) or CO₂Me (4,4′-dimethoxycarbonyl-2,2′-bipyridine). Efficient photocatalytic water oxidation was achieved by tuning the photochemical properties of the Ru complexes on the BPy-PMO through the incorporation of electron-donating or electron-withdrawing functionalities. The reaction turnover number based on the amount of the Ru complex was improved to 20, which is higher than values previously obtained from PMO systems acting as water oxidation photocatalysts.

Ruthenium complex photosensitizer fixed on 2,2′-bipyridine bridged-periodic mesoporous organosilica with iridium oxide exhibits an efficient photocatalytic water oxidation.     

Smooth and large scale organometallic complex film by vapor-phase ligand exchange reaction

A simple and reliable method for the formation of smooth and large-scale organometallic complex thin films was developed. We applied chemical vapor deposition (CVD) for this. From the vapor-phase reaction of Mo(CO)₆ and 2,2′-bipyridine, large-scale and highly smooth Mo(CO)₄(2,2′-bipy) films were obtained. Regardless of the thickness, they show a high smoothness and stability in ambient conditions. Chemical structure and composition of the resulting film were confirmed by ¹H-NMR, Raman, FT-IR spectroscopy and elemental analyses. Smooth and uniform surface of the resulting films was characterized using AFM. We believe that our method will provide great opportunities for the fundamental studies of traditional organometallic complexes and their applications by taking advantages of thin film geometry.

Highly-smooth Mo(CO)₄(2,2′-bipy) thin film showing a color gradient depending on the thickness can be obtained by vapor-phase ligand exchange reaction.

Fabrication of organometallic complexes (OMCs) into high-quality thin films would enable observation of previously-unseen chemical reactions, and allow elucidation of properties that are difficult to detect in other phases than thin films. In addition, the thin films would have various applications in fields such as electronics, photoelectronics, optics, photonics, magnets and spintronics.^1–6 Most attempts to obtain high-quality OMC films have tried to coat pre-synthesized target complexes.⁷ However, these methods were mostly unsuccessful and if successful were not easily applied to general OMCs. Therefore, a new reliable method for the formation of high-quality OMC films is sought.Direct formation of OMC films on a target substrate is a promising method because of their good reactivity and potentially interesting electrical and optical properties. OMCs have been synthesized in solution phase, but this method is more appropriate for obtaining three-dimensional structures than for films. Also, physical vapor deposition methods to pre-synthesize OMCs are also not appropriate due to their low vapor pressure and the possibility of decomposition. Hence, development of efficient synthesis methods to obtain large-scale and uniform OMC film remains a challenge.Chemical vapor deposition (CVD) is an effective method to produce large-scale two-dimensional materials^8,9 and to form films of polymers¹⁰ and metal–organic frameworks.¹¹ Here, we report a rapid and highly efficient CVD method that uses in situ vapor-phase chemical reactions of precursors to synthesize highly-uniform thin films of OMCs. This method facilitates direct reaction of precursors without any disturbance by solvent or impurities, and therefore induces facile formation of pure, highly-uniform and smooth OMC films. It is useful for electrocatalytic CO₂ reduction¹² and ligand exchange reaction.¹³ We exploited a vapor-phase ligand exchange reaction between hexacarbonylmolybdenum(0) (Mo(CO)₆) and 2,2′-bipyridine (2,2′-bipy). The reaction was conducted in a CVD system within 5 min to yield highly-uniform, smooth, and large-scale Mo(CO)₄(2,2′-bipy) thin film for the first time. We then used the Mo(CO)₄(2,2′-bipy) film in organometallic thin-film devices and measured their electrical properties.High-quality OMC thin films were prepared using single-step CVD. The metal precursor was Mo(CO)₆ and the ligand precursor was 2,2′-bipy. The goal was to obtain Mo(CO)₄(2,2′-bipy) by a reaction that proceeds well in solution phase.^12,13 Considering the vaporization temperature of Mo(CO)₆ (94.45 °C) and 2,2′-bipy (113.75 °C) (Fig. S1^†), we chose 123 °C as a target temperature for efficient and simultaneous evaporation of precursors. In the CVD system for vapor-phase organometallic reaction (Fig. 1a), Mo(CO)₆ powder was placed 13.5 cm upstream from the center. And 2,2′-bipy powder was placed at the center. This arrangement exploits the temperature gradient in the furnace, and the higher vaporization temperature of 2,2′-bipy than of Mo(CO)₆. A SiO₂/Si target substrate was placed downstream from the center of the tube to collect product efficiently. The quartz tube was flushed using Ar, then the tube furnace was heated from room temperature to the target temperature at 10 °C min⁻¹ (Fig. 1b). After 5 min of reaction at target temperature, the power to the furnace was turned off and the sample was allowed to cool passively to room temperature.Open in a separate windowFig. 1(a) Experimental scheme of the CVD system for the synthesis of Mo(CO)₄(2,2′-bipy) thin film. (b) Molecular structure Mo(CO)₄(2,2′-bipy) obtained by vapor-phase ligand exchange reaction between Mo(CO)₆ and 2,2′-bipy.The resulting large-scale Mo(CO)₄(2,2′-bipy) film was highly uniform and had no notable physical defects or chunks (Fig. 2). We confirmed that the product did not undergo thermal decomposition at operating temperature (123 °C) (Fig. S2 and Table S1^†). The surface of the resulting film was examined using a tapping-mode atomic force microscope (AFM). To measure the thickness of the resulting film, we etched away the film except for a part that was covered using Kapton tape as a shadow mask. The film was treated using CF₄ at flow rate of 40 sccm and O₂ plasma at 5 sccm with power of 150 W power, respectively. Etching time was determined depending on film thickness, from 30 to 90 min. After the process, the measured thickness was 38.6 nm (Fig. S3a^†); the height distribution measured by AFM showed that the Mo(CO)₄(2,2′-bipy) film was highly smooth and uniform surface (root mean square roughness r_RMS = 0.267 nm, Fig. 2b), which is similar to that of a bare SiO₂/Si substrate (r_RMS = 0.249 nm, Fig. S3b^†). A scanning electron microscopy (SEM) image (Fig. S4^†) of the obtained film shows uniform and homogenous surfaces over a large area. Energy-dispersive electron energy loss spectroscopy (EELS) analysis confirmed the presence of Mo, C, N, and O (Fig. S5^†). These results demonstrate that CVD is a highly efficient approach to obtain highly-uniform OMC films.Open in a separate windowFig. 2(a) Optical microscopy image, photograph (inset), and (b) AFM image of the obtained Mo(CO)₄(2,2′-bipy) thin film. (c) Raman spectra of the Mo(CO)₄(2,2′-bipy) powder (purple), and two precursors (Mo(CO)₆ (green), 2,2′-bipy (coral blue)). (d) FT-IR spectrum of Mo(CO)₄(2,2′-bipy) thin film showing four carbonyl stretching bands.The chemical structure of the resulting film was confirmed by Raman and FT-IR analyses (Fig. 2d). For a direct comparison of the chemical structure of the resulting film with a reference, we separately synthesized Mo(CO)₄(2,2′-bipy) bulk powder by using a microwave-assisted synthesis method described elsewhere¹⁴ (ESI^†). The obtained powder was red (Fig. S6^†) and its structure as confirmed by ¹H-NMR was identical to that reported in the reference paper.¹⁴ Raman spectra (Fig. 2c) were obtained from precursors, product film, and reference powder. The carbonyl stretching band was observed at 1900–2000 cm⁻¹, and several bipyridine stretching bands were observed at 1100–1600 cm⁻¹.¹⁵ The stretching bands of the aromatic rings of 2,2′-bipy (asterisks) and the carbonyl stretching bands (triangle) were clearly resolved. The vibrational band of Mo(CO)₄(2,2′-bipy) film (red) is almost identical with the reference Mo(CO)₄(2,2′-bipy) powder (purple).To identify chemical species observed in Raman spectra, we conducted density functional theory (DFT) calculations using Dmol³ modules in Material Studio program packages (details in ESI^†). The six representative bands observed at 1170.8, 1263.5, 1322.0, 1535.5, 1563.9 and 1600.1 cm⁻¹ in the Raman spectrum of Mo(CO)₄(2,2′-bipy) film were confirmed as molybdenum-coordinated bipyridine ligand stretching bands (red), which are shifted and split from the original stretching bands of bipyridine precursor (1147.6, 1236.4, 1303.4, 1574.1, and 1590.2 cm⁻¹, blue). Also, the carbonyl stretching band shifted from 2005.9 cm⁻¹ to 1888.2 cm⁻¹ because to the new coordination bonds between molybdenum and 2,2′-bipy ligand has a weaker π-accepting ability than the previously-bonded carbonyl ligands.¹⁶ The DFT calculations generated Raman vibrational modes of precursors and film (ESI Videos^†). Also, we measured the FT-IR spectrum of Mo(CO)₄(2,2′-bipy) film by using an attenuated total reflection (ATR) mode (650–4000 cm⁻¹). The spectrum (Fig. 2d) shows carbonyl stretching bands at 2014, 1898, 1866, and 1824 cm⁻¹, which correspond respectively to A^1a₁, B₁, A^1b₁, and B₂ vibrational modes of carbonyl ligands interacting to the six-coordinated molybdenum complex; this result is a good match to reference data.¹⁷For further characterization, we measured ¹H-NMR of dissolved Mo(CO)₄(2,2′-bipy) film in CDCl₃. The NMR peaks (Fig. S7,^† triangles) match well with the reference NMR peaks of Mo(CO)₄(2,2′-bipy) powder,¹⁴ and also confirmed the presence of small amount of 2,2′-bipy precursor (squares). Grazing-incidence wide-angle X-ray scattering (GI-WAXS) measurements (Fig. S8^†) we confirmed the amorphous structure of the resulting film.One of the big advantages of CVD is that the thickness of the resulting film can be controlled easily by changing the amount of precursors. Mo(CO)₄(2,2′-bipy) films were formed on SiO₂/Si substrate by using different amounts of precursors; the films showed a continuous color gradient that depended on the thickness (Fig. 3a). The thickness can be controlled from the range of tens of nanometers to micron scale; all surfaces were highly smooth (Fig. S9^†).Open in a separate windowFig. 3(a) Photograph of Mo(CO)₄(2,2′-bipy) films showing a continuous color gradient depending on the thickness. The rightmost sample is a bare SiO₂/Si substrate. (b) I–V characteristic curve of Mo(CO)₄(2,2′-bipy) thin film; inset: photograph of the fabricated device. (c) I–V characteristics at rt ≤ T ≤ 100 °C for DC voltage −40 to 40 V.To exploit the geometrical advantage of the thin film for device fabrication, field-effect transistor (FET) electronic devices with a channel length of 20 mm (Fig. 3b, inset) were fabricated (ESI and Fig. S10^†). The I_ds–V_ds curve (Fig. 3b) of the resulting device indicated that the highest electrical conductance was 1.90 × 10⁻⁹ S, and the highest conductivity was 1.99 × 10⁻⁵ S m⁻¹. The linear characteristic of I–V curve is a sign of ohmic contact between film and electrode, as a consequence of the uniform and smooth surface of Mo(CO)₄(2,2′-bipy) film. The electrical conductance of Mo(CO)₄(2,2′-bipy) film increased as the temperature was increased from room temperature to 100 °C (Fig. 3c); this result shows the semiconducting nature of the Mo(CO)₄(2,2′-bipy) film. To compare the electrical property of film with reference powder, Mo(CO)₄(2,2′-bipy) powder was pelletized and fabricated on a SiO₂/Si substrate. The pellet was rough and thick, so we used silver paste as an adhesive electrode. The I–V characteristic curve (Fig. S11^†) of Mo(CO)₄(2,2′-bipy) pellet exhibits non-ohmic current–voltage characteristics between the pellet and the electrode, and eventually failed to measure the electrical property of the complex. These results demonstrate that the intrinsic properties of organometallic materials requires synthesis of uniform and smooth organometallic film.^18,19In summary, we synthesized large-scale, highly-uniform, smooth, and thickness-controllable Mo(CO)₄(2,2′-bipy) thin films by vapor-phase ligand exchange reaction that exploits chemical vapor deposition (CVD). Our strategy facilitates the vapor-phase reaction of precursors without any disturbance of solvent or impurities, and also yields a suitable smooth film geometry that is advantageous for various electrical and optical device applications. FET devices that use Mo(CO)₄(2,2′-bipy) thin film exhibit semiconducting behaviour. We believe that these results provide insights that will guide development of novel strategies to synthesize various OMC films for use in various electrical and optical applications.     

A novel 3D Cd(ii) coordination polymer generated via in situ ligand synthesis involving C–O ester bond formation

A novel 3D Cd(ii) coordination polymer {[Cd(ddpa)(2,2′-bpy)]·H₂O}_n (1) (H₂ddpa = 5,10-dioxo-5,10-dihydro-4,9-dioxapyrene-2,7-dicarboxylic acid, 2,2′-bpy = 2,2′-bipyridine) is hydrothermally synthesized in situ, and the influencing factors and mechanism for the in situ reaction are briefly discussed. The synthesis of 1 requires the formation of a new C–O ester bond. This current study confirms that metal ions and N-donor ligands play important roles in the domination of the in situ ligand from 6,6′-dinitro-2,2′,4,4′-biphenyltetracarboxylic acid (H₄dbta). Furthermore, the structure, thermal stability and photoluminescent property of 1 are also investigated.

A 3D Cd(ii) coordination polymer comprising ligand molecules not included in the original reaction mixtures but instead formed via in situ ligand synthesis involving a C–O ester bond.     

Effects of template molecules on the structures and luminescence intensities of a series of porous Tb-MOFs based on the 2-nitroterephthalate ligand

Four novel porous Tb(iii) metal–organic frameworks (Tb-MOFs) have been designed and prepared hydrothermally from 2-nitroterephthalate (2-H₂ntp), namely {[Tb(2-ntp)_1.5(H₂O)]·H₂O}_n (1), {[Tb(2-ntp)₂(H₂O)]·4,4′-Hbipy}_n (2), {[Tb(2-ntp)₂(H₂O)]·2,4-Hbipy}_n (3), and {[Tb(2-ntp)₂(H₂O)]·(1,4-H₂bbi)_0.5}_n (4) (4,4′-bipy = 4,4′-bipyridine; 2,4-bipy = 2,4-bipyridine; 1,4-bbi = 1,4-bisbenzimidazole). X-ray diffraction structural analyses show these Tb-MOFs are porous and are based on Tb³⁺ ions and 2-nitroterephthalate, in which water molecules (1) or protonated N-donor ligands (2–4) exist as templates. The fluorescence properties of complexes 1–4 could be associated with the characteristic peaks of Tb(iii) ions, and the existence of different guest molecules affects the intensities of peaks, which means that these could be potential fluorescence materials, with intensities adjusted using guests.

Four porous Tb-MOFs based on 2-nitroterephthalate are described, in whose pores water (1) or co-ligands (2–4) exist in the pores as templates. The emissions could be related to the characteristic peaks of Tb(iii) ions, and their intensities are affected and adjusted by templates.     

New ruthenium polypyridyl complexes as potential sensors of acetonitrile and catalysts for water oxidation

New ruthenium(ii) polypyridyl complexes of formulae [RuCl(Me₂Ntrpy)(bpy-OMe)]Cl, 1, and [Ru(Me₂Ntrpy)(bpy-OMe)(OH₂)](CF₃SO₃)₂, 2, with Me₂Ntrpy = 4′-N,N-dimethylamino-2,2′:6′,2′′-terpyridine and bpy-OMe = 4,4′-dimethoxy-2,2′-bipyridine, were synthetized and characterized by spectroscopic and electrochemical techniques. Besides, [Ru(Me₂Ntrpy)(bpy-OMe)(NCCH₃)]²⁺, 3, was obtained and characterized by UV-vis spectroscopy in acetonitrile solution. All experimental results were complemented with DFT and TD-DFT calculations. The complete structure of complex 1 was determined by X-ray diffraction, evidencing that the Ru–N and Ru–Cl bond lengths are longer than those determined in [RuCl(trpy)(bpy)](PF₆). The strong electron donating properties of the substituents of both bpy and trpy rings in complexes 1 and 2 led to their potential applications for detecting traces of acetonitrile as a contaminant in aqueous solutions of radiopharmaceuticals and to utilization of complex 2 as a promising candidate for catalyzing water oxidation processes.

New mononuclear polypyridyl Ru(ii) complexes were synthesized and fully characterized. These species can be potentially applied for detection of CH₃CN as a contaminant in radiopharmaceuticals used in PET studies or for catalysing water oxidation.     

Multiple chemical modifications and Cd2+ adsorption characteristics of sludge-based activated carbon

Sludge resource utilization is commonly realized through carbonization, but the use of direct carbonization to obtain sludge-based activated carbon (SAC) is not functional yet. The multiple chemical modifications were carried out to achieve N-doping and pore-making to modify SAC. The SAC_U–PF′ was synthesized by activating sludge simultaneously with uric acid and potassium ferrate. Moreover, SAC_N′, SAC_U, and SAC_PF′ were prepared with no additives, uric acid, and potassium ferrate, respectively. The results indicated that the different modifications affected the chemical properties and structure of SAC. The BET of SAC_U–PF′ was 56.73 m² g⁻¹, which was higher than that of SAC_N′ and SAC_PF′. SAC_U–PF′ possessed abundant functional groups, such as C N and C–O. The adsorption capacity of SAC_U–PF′ for Cd²⁺ was 9.69 mg g⁻¹, 5.5 times that of SAC_N′, the adsorption process of Cd²⁺ by SAC_U–PF′ fitted well for the second-order kinetic model and Langmuir isothermal adsorption model. The XPS and chemical analysis revealed that SAC_U–PF′ and Cd²⁺ were bonded by functional groups, and the Cd²⁺ removal by SAC_U–PF′ was through complexation, anion exchange, electrostatic attraction, and pore filling. The SAC_U–PF′ was exhibited different removal capacities for different metals, Pb²⁺ and Mn²⁺ correspond to adsorption capacities of 4.9 and 8.1 mg g⁻¹. In addition, the adsorbed SAC_U–PF′ can be regenerated by sodium hydroxide. The study highlights the importance of multiple chemical modifications performed on SAC, the double coupled chemical modifications to ensure its good performance in the treatment of heavy metals in wastewater treatment.

The multiple chemical modifications were carried out to achieve N-doping and pore-making to modify sludge-based activated carbon (SAC_U–PF′). SAC_U–PF′ possessed abundant functional groups and high adsorption capacity of Cd²⁺.     

Two d10 luminescent metal–organic frameworks as dual functional luminescent sensors for (Fe3+,Cu2+) and 2,4,6-trinitrophenol (TNP) with high selectivity and sensitivity

Two luminescent 3D supramolecular structures [Cd₃(L)₂(2,2-bipy)₂](DMF)₃(CH₃CH₂OH)₂(H₂O) (1) and [Zn₃(L)₂(2,2-bipy)₂(DMF)₂](DMF)₂(CH₃CH₂OH)₂(H₂O) (2) (H₃L = 4,4′,4′′-nitrilotribenzoic acid) have been successfully synthesized under solvothermal conditions using Cd(NO₃)₂·4H₂O or Zn(NO₃)₂·6H₂O as the metal sources, and 4,4′,4′′-nitrilotribenzoic acid (H₃L), 2,2-bipy as the ligands in DMF solvent. Compound 1 displays a bi-nodal (2,3,6)-coordinated net with {8³}₂{8⁶·12⁶·16³}{8}₆ topology, compound 2 can be described as a (3,6)-connected 2-nodal net with kgd topology. The phase purity of compound 1 and 2 is characterized by X-ray powder diffraction (XRPD), thermogravimetric analysis (TGA) and Fourier transform infrared (FT-IR) spectroscopy. Compound 1 and 2 can serve as effective luminescent sensors for Fe³⁺, Cu²⁺ and TNP via luminescent quenching.

Two luminescent 3D supramolecular structures which serve as effective luminescent sensors for Fe³⁺, Cu²⁺ and TNP via luminescent quenching have been synthesized under solvothermal conditions.     

Highly sensitive detection of nitrobenzene by a series of fluorescent 2D zinc(ii) metal–organic frameworks with a flexible triangular ligand

Four fluorescent zinc(ii) metal–organic frameworks, namely [Zn(HCIA)(4,4′-bipy)] (1), [Zn₂(CIA)(OH)(1,4-bibz)_1.5]·H₂O (2), [Zn(CIA)(OH) (4,4′-bbpy)] (3), and [Zn₂(HCIA) (4,4′-bimp)]·H₂O (4), were prepared hydrothermally with a flexible triangular ligand (H₃CIA) and a series of linear N-donor ligands (H₃CIA = 5-(2-carboxybenzyloxy) isophthalic acid, 4,4′-bipy = 4,4′-bipydine, 1,4-bibz = 1,4-bis(1-imidazoly)benzene; 4,4′-bbpy = 4,4′-bis (imidazolyl) biphenyl; 4,4′-bimp = 4,4′-bis (imidazole-1-ylethyl) biphenyl). Structural analyses revealed that complex 1 exhibited a 2D brick-like network structure based on the basic bimetallic ring, 2 was also a 2D interspersed structure from the 1D tubular structure, compound 3 possessed a 2D (4,4) network with 4,4′-bbpy occupying the holes, and complex 4 displayed a 2D network from the 1D ladder-like chain. The thermal stabilities and fluorescent properties of these complexes were investigated in the solid state. The fluorescent sensing experiments revealed that all Zn-MOFs could highly sensitively detect nitrobenzene in aqueous solution, which indicated that these materials can be used as fluorescent probes for the detection of nitrobenzene.

Four fluorescent 2D Zn-MOFs based on a flexible triangular ligand and linear N-donor ligands are hydrothermally prepared and used to detect nitrobenzene in aqueous solution with high sensitivity, demonstrating their potential as fluorescent sensors.     

Base-promoted lipase-catalyzed kinetic resolution of atropisomeric 1,1′-biaryl-2,2′-diols

Herein we report a dramatic acceleration of the lipase-catalyzed kinetic resolution of atropisomeric 1,1′-biaryl-2,2′-diols by the addition of sodium carbonate. This result likely originates from the increased nucleophilicity of the phenolic hydroxyl group toward the acyl-enzyme intermediate. Under these conditions, various substituted C₂-symmetric and non-C₂-symmetric binaphthols and biphenols were efficiently resolved with ∼50% conversion in only 13–30 h with excellent enantioselectivity.

The addition of a stoichiometric amount of Na₂CO₃ dramatically accelerates the lipase-catalyzed kinetic resolution of a range of atropisomeric 1,1′-biaryl-2,2′-diols.     

Solvent-tuned charge-transfer properties of chiral Pt(ii) complex and TCNQ˙− anion adducts

A new pair of adducts comprising one chiral Pt(ii) complex cation, [Pt((−)-L₁)(Dmpi)]⁺ ((−)-1) or [Pt((+)-L₁)(Dmpi)]⁺ ((+)-1) [(−)-L₁ = (−)-4,5-pinene-6′-phenyl-2,2′-bipyridine, (+)-L₁ = (+)-4,5-pinene-6′-phenyl-2,2′-bipyridine, Dmpi = 2,6-dimethylphenylisocyanide], together with one TCNQ˙⁻ anion have been obtained, and the structures have been confirmed via single-crystal X-ray crystallography and infrared (IR) spectroscopy. The chiral Pt(ii) cation and TCNQ˙⁻ anion are dissociated in MeOH solution, while charge transfer adducts are formed in H₂O solution, leading to perturbation of the electronic structure and alteration of the chiral environment, as evidenced by the differences in the UV-vis absorption and electronic circular dichroism spectra. The solvent-tuned charge-transfer properties also have been validated through emission and resonance light scattering spectra. The interesting findings may have potential applications in the development of black absorbers and wide band gap semiconductors.

A new couple of charge transfer adducts comprising of one chiral Pt(ii) complex cation together with one TCNQ˙⁻ anion have been prepared, and solvent-induced variances of absorption, luminescence as well as chiral spectra have been investigated.     

Hollow waxberry-like cobalt–nickel oxide/S,N-codoped carbon nanospheres as a trifunctional electrocatalyst for OER,ORR, and HER

With the aggravation of the energy crisis, increasing attention has been paid to electrocatalytic technology for renewable energy devices. In particular, the research on catalysts towards the oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and hydrogen evolution reaction (HER) has become more urgent, and the development of multifunctional electrocatalysts has become a research trend. Here we report the synthesis of waxberry-like cobalt–nickel oxide/S,N-codoped carbon hollow nanocomposites as trifunctional catalysts. Uniform cobalt–nickel glycerate solid spheres are first synthesized as the precursor and subsequently chemically transformed into cobalt–nickel oxide/S,N-codoped carbon hollow nanospheres. Benefiting from the synergistic coupling of cobalt–nickel oxide and S,N-codoped carbon nanocomposites, hierarchical porosity and hollow structure, the cobalt–nickel oxide/S,N-codoped carbon nanohybrids exhibit superior trifunctional electrocatalytic activity and durability towards OER, ORR, and HER in alkaline media.

The catalyst is assembled from small nanoparticles in the shape of a bayberry, and exhibits superior trifunctional electrocatalytic activity.     

Convergent access to bis-1,2,4-triazinyl-2,2′-bipyridines (BTBPs) and 2,2′-bipyridines via a Pd-catalyzed Ullman-type reaction

Multidentate, soft-Lewis basic, complexant scaffolds have displayed significant potential in the discrete speciation of the minor actinides from the neutron-absorbing lanthanides resident in spent nuclear fuel. Efforts to devise convergent synthetic strategies to targets of interest to improve liquid–liquid separation outcomes continue, but significant challenges to improve solubility in process-relevant diluents to effectively define meaningful structure–activity relationships remain. In the current work, a synthetic method to achieve the challenging 2,2′-bipyridine bond of the bis-1,2,4-triazinyl-2,2′-bipyridine (BTBP) complexant class leveraging a Pd-catalyzed Ullman-type coupling is reported. This convergent strategy improves upon earlier work focused on linear synthetic access to the BTBP complexant moiety. Method optimization, relevant substrate scope and application, as well as a preliminary mechanistic interrogation are reported herein.

Access to functionalized BTBP complexants through a reductive coupling strategy decreases linearity of common synthetic strategies towards these relevant materials for separations.     

Electronic effects on the mechanism of the NAD+ coenzyme reduction catalysed by a non-organometallic ruthenium(ii) polypyridyl amine complex in the presence of formate

In the present study, electronic effects on the mechanism of the NAD⁺ coenzyme reduction in the presence of formate, catalysed by a non-organometallic ruthenium(ii) polypyridyl amine complex, were investigated. The [Ru^II(terpy)(ampy)Cl]Cl (terpy = 2,2′:6′,2′′-terpyridine, ampy = 2-(aminomethyl)pyridine) complex was employed as the catalyst. The reactions were studied in a water/ethanol mixture as a function of formate, catalyst, and NAD⁺ concentrations at 37 °C. The overall process was found to be 11 to 18 times slower than for the corresponding ethylenediamine (en) complex as the result of π-back bonding effects of the ampy ligand. The mechanistic studies revealed a complete set of reactions that accounted for the overall catalytic cycle based on a formate-induced hydride transfer reaction to form the reduced coenzyme, NADH. The geometries of the ruthenium(ii)-ampy complexes involved in the catalytic cycle and free energy changes for the main steps were predicted by DFT calculations. Similar calculations were also performed for the analogues ruthenium(ii)-en and ruthenium(ii)-bipy complexes (bipy = 2,2′-bipyridine). The DFT calculated energies show that both the solvent-formato exchange and the formato-hydrido conversion reactions have negative (favourable) energies to proceed spontaneously. The reactions involving the en complex have the more negative (favourable) reaction energies, followed by the ampy complex, in agreement with faster reactions for en complexes and slower reactions for bipy complexes than for ampy complexes.

The graphical abstract represents the overall catalytic cycle in which the non-organometallic Ru(ii) formato complex releases CO₂ and transfers hydride to NAD⁺ to form NADH coenzyme.     

Reactive molecular dynamics simulation of the high-temperature pyrolysis of 2,2′,2′′,4,4′,4′′,6,6′,6′′-nonanitro-1,1′:3′,1′′-terphenyl (NONA)

2,2′,2′′,4,4′,4′′,6,6′,6′′-Nonanitro-1,1′:3′,1′′-terphenyl (NONA) is currently recognized as an excellent heat-resistant explosive. To improve the atomistic understanding of the thermal decomposition paths of NONA, we performed a series of reactive force field (ReaxFF) molecular dynamics simulations under extreme conditions of temperature and pressure. The results show that two distinct initial decomposition mechanisms are the homolytic cleavage of the C–NO₂ bond and nitro–nitrite (NO₂ → ONO) isomerization followed by NO fission. Bimolecular and fused ring compounds are found in the subsequent decomposition of NONA. The product identification analysis under finite time steps showed that the gaseous products are CO₂, N₂, and H₂O. The amount of CO₂ is energetically more favorable for the system at high temperature or low density. The carbon-containing clusters are a favorable growth pathway at low temperatures, and this process was further demonstrated by the analysis of diffusion coefficients. The increase of the crystal density accelerates the decomposition of NONA judged by the analysis of reaction kinetic parameters and activation barriers. In the endothermic and exothermic stages, a 20% increase in NONA density increases the activation energies by 3.24 and 0.48 kcal mol⁻¹, respectively. The values of activation energies (49.34–49.82 kcal mol⁻¹) agree with the experimental data in the initial decomposition stage.

The bimolecular and fused ring compounds are found in the high-temperature pyrolysis of NONA using ReaxFF molecular dynamics simulations.     

The shiny side of copper: bringing copper(i) light-emitting electrochemical cells closer to application

Heteroleptic [Cu(P^P)(N^N)][PF₆] complexes, where N^N is 5,5′-dimethyl-2,2′-bipyridine (5,5′-Me₂bpy), 4,5,6-trimethyl-2,2′-bipyridine (4,5,6-Me₃bpy), 6-(tert-butyl)-2,2′-bipyridine (6-tBubpy) and 2-ethyl-1,10-phenanthroline (2-Etphen) and P^P is either bis(2-(diphenylphosphino)phenyl)ether (POP, PIN [oxydi(2,1-phenylene)]bis(diphenylphosphane)) or 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (xantphos, PIN (9,9-dimethyl-9H-xanthene-4,5-diyl)bis(diphenylphosphane)) have been synthesized and their NMR spectroscopic, mass spectrometric, structural, electrochemical and photophysical properties were investigated. The single-crystal structures of [Cu(POP)(5,5′-Me₂bpy)][PF₆], [Cu(xantphos)(5,5′-Me₂bpy)][PF₆], [Cu(POP)(6-tBubpy)][PF₆], [Cu(POP)(4,5,6-Me₃bpy)][PF₆]·1.5Et₂O, [Cu(xantphos)(4,5,6-Me₃bpy)][PF₆]·2.33CH₂Cl₂, [Cu(POP)(2-Etphen)][PF₆] and [Cu(xantphos)(2-Etphen)][PF₆] are described. While alkyl substituents in general exhibit electron-donating properties, variation in the nature and substitution-position of the alkyl group in the N^N chelate leads to different effects in the photophysical properties of the [Cu(P^P)(N^N)][PF₆] complexes. In the solid state, the complexes are yellow to green emitters with emission maxima between 518 and 602 nm, and photoluminescence quantum yields (PLQYs) ranging from 1.1 to 58.8%. All complexes show thermally activated delayed fluorescence (TADF). The complexes were employed in the active layer of light-emitting electrochemical cells (LECs). The device performance properties are among the best reported for copper-based LECs, with maximum luminance values of up to 462 cd m⁻² and device half-lifetimes of up to 98 hours.

Heteroleptic copper(i) complexes with bisphosphanes and astutely tuned N^N chelating ligands as emitters give bright LECs with record-breaking stability.     

Mesoporous silica–carbon composites fabricated by a universal strategy of hydrothermal carbonization: controllable synthesis and applications

Mesoporous silica–carbon composite materials, with homogeneous and thickness-controllable carbon coating, were synthesized by using a universal strategy of hydrothermal carbonization, and the carbon layer could be coated on the surface of ordered and disordered mesoporous silica. The electrostatic interaction between amino-modified silica and hydrothermal carbon was regarded as the main driving force for the formation of homogeneous carbon coverage on the silica surface. The obtained composites showed high graphitization degree, and controlled morphology (shape and particle size) and pore size by adjusting the species of carriers and hydrothermal conditions. The application results demonstrated that a thin carbon layer possessed high adsorption capacities for dyes, and the composite could be rapidly recovered by sedimentation (10 min) after adsorption with 30 μm spherical silica gel as the carrier. Besides, baseline chromatographic separation of oligosaccharide isomers could be achieved on the silica–carbon column. These results indicated that the silica–carbon composites should be promising functional materials for the large-molecule-involving processes such as adsorption and chromatographic separation.

A carbon layer with controlled thickness can be coated on the surface of mesoporous silica through the hydrothermal carbonization strategy.     

Ruthenium carboranyl complexes with 2,2′-bipyridine derivatives for potential bimodal therapy application

Ruthenium complexes of carboranyl ligands offer the possibility of dual action (chemo + radiotherapy) that might result in significant clinical benefits. In that frame, we describe herein the development of ruthenium–carboranyl complexes bearing bipyridyl derivatives with the general formula [3-CO-3,3-{κ²-4,4′-R₂-2,2′-bipy}-closo-3,1,2-RuC₂B₉H₁₁] (R = CH₃, RuCB1 or R = CH₂OH, RuCB2). Both compounds crystallized in the monoclinic system, showing the expected three-legged piano stool structure. The ruthenacarboranes are stable in cell culture media and were tested against two cell lines that have shown favorable clinical responses with BNCT, namely melanoma (A375) and glioblastoma (U87). RuCB1 shows no cytotoxic activity up to 100 μM while RuCB2 showed moderate activity for both cell lines. Cell distribution assays showed that RuCB2 presents high boron internalization that is proportional to the concentration used indicating that RuCB2 presents features to be further studied as a potential anticancer bimodal agent (chemo + radiotherapy).

The substituents at the bipyridine lead to different cell uptake and stability.     

Microwave-assisted synthesis of ruthenium(ii) complexes containing levofloxacin-induced G2/M phase arrest by triggering DNA damage

Ru(ii) complexes have attracted increasing attention as promising antitumor agents for their relatively low toxicity, high affinity to DNA molecules, and correlation with multiple targets. Meanwhile, quinolones are synthetic antibacterial agents widely used in the clinical practice. In this paper, two novel Ru(ii) complexes coordinated by levofloxacin (LOFLX), [Ru(bpy)₂(LOFLX)]·2ClO₄ (1), and [Ru(dmbpy)₂(LOFLX)]·2ClO₄ (2) (bpy = 2,2′-bipyridine, dmbpy = 4,4′-dimethyl-2,2′-bipyridine) were synthesized with high efficiency under microwave irradiation and characterized by ESI-MS, ¹H NMR, and ¹³C NMR. The binding behavior of these complexes with double-strand calf thymus DNA(CT-DNA) was investigated using spectroscopy, molecular docking, and density functional theory calculations. Results showed that 2 exhibited higher binding affinity than 1 and LOFLX. Further studies showed that 2 could induce the G2/M phase arrest of A549 cells via DNA damage. In summary, these results indicated that 2 could be developed as a potential anticancer agent in treatment of lung cancer through the induction of cell cycle arrest at G2/M phase by triggering DNA damage.

This study showed that levofloxacin-based ruthenium(ii) complex 2 effectively inhibited the growth of A549 cells by inducing G2/M phase arrest through triggering DNA damage.