Selective Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid Using O2 and a Photocatalyst of Co-thioporphyrazine Bonded to g-C3N4.

Selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) is one of the key reactions for producing chemical commodities from biomass and their derivatives. The challenge for this reaction is to develop an efficient catalytic process that can be conducted under mild conditions (room temperature and atmospheric pressure, using oxygen molecules in air as the oxidant) and a recyclable catalyst. Herein we report a photocatalyst of cobalt thioporphyrazine (CoPz) dispersed on g-C3N4 (abbreviated as CoPz/g-C3N4), which exhibits excellent catalytic activity toward the selective oxidation of HMF into FDCA under simulated sunlight using oxygen molecules in air as a benign oxidant. For example, an FDCA yield of 96.1% in an aqueous solution at pH = 9.18 is achieved at ambient temperature and air pressure. At lower pH (4.01), the product generated is 2,5-diformylfuran. Hence, it is possible to control the reaction outcome by control of the pH of the reaction system. g-C3N4 itself is not a suitable catalyst for the selective oxidation because under the experimental conditions g-C3N4 generates hydroxyl radicals that initiate processes that oxidize HMF directly to CO2 and H2O. CoPz on the other hand activates O2 to give singlet oxygen (1O2), which more controllably oxidizes HMF to FDCA albeit at a more moderate yield (36.2%). The strong interaction between the CoPz and g-C3N4 in the CoPz/g-C3N4 catalyst is experimentally evidenced, which not only improves accessibility of the CoPz sites and makes the catalyst recyclable but also disables the hydroxyl radical generation by g-C3N4 and promotes 1O2 generation on the CoPz sites, significantly enhancing the catalytic performance. This study demonstrates the potential for efficient non-noble metal photocatalysts for organic transformations driven by sunlight.

Selective oxidation of benzyl alcohols to benzoic acid catalyzed by eco-friendly cobalt thioporphyrazine catalyst supported on silica-coated magnetic nanospheres.

A novel magnetically recoverable thioporphyrazine catalyst (CoPz(S-Bu)8/SiO2@Fe3O4) was prepared by immobilization of the cobalt octkis(butylthio) porphyrazine complex (CoPz(S-Bu)8) on silica-coated magnetic nanospheres (SiO2@Fe3O4). The composite CoPz(S-Bu)8/SiO2@Fe3O4 appeared to be an active catalyst in the oxidation of benzyl alcohol in aqueous solution using hydrogen peroxide (H2O2) as oxidant under Xe-lamp irradiation, with 36.4% conversion of benzyl alcohol, about 99% selectivity for benzoic acid and turnover number (TON) of 61.7 at ambient temperature. The biomimetic catalyst CoPz(S-Bu)8 was supported on the magnetic carrier SiO2@Fe3O4 so as to suspend it in aqueous solution to react with substrates, utilizing its lipophilicity. Meanwhile the CoPz(S-Bu)8 can use its unique advantages to control the selectivity of photocatalytic oxidation without the substrate being subjected to deep oxidation. The influence of various reaction parameters on the conversion rate of benzyl alcohol and selectivity of benzoic acid was investigated in detail. Moreover, photocatalytic oxidation of substituted benzyl alcohols was obtained with high conversion and excellent selectivity, specifically conversion close to 70%, selectivity close to 100% and TON of 113.6 for para-position electron-donating groups. The selectivity and eco-friendliness of the biomimetic photocatalyst give it great potential for practical applications.

[µ-N (1),N (2)-Bis(pyridin-2-yl)hydrazine-1,2-dicarbothio-amidato]bis-[chlorido-copper(II)].

The binuclear title compound, [Cu2(C12H10N6S2)Cl2], possesses twofold rotational symmetry. The Cu(II) atom occupies a four-coordinate pseudo-tetra-hedral environment bound to one S atom, one imine N atom and one pyridine N atom from the N(1),N(2)-bis-(pyridin-2-yl)hydrazine-1,2-dicarbo-thio-amidate ligand, and one Cl(-) anion. The metal atoms are connected via the bis-tridentate ligand into a binuclear structure. The mol-ecule is bow-shaped with the pyridine rings inclined to one another by 51.56 (14)°. In the crystal, N-H⋯Cl hydrogen bonds lead to the formation of ribbons propagating along [001]. These ribbons are connected via C-H⋯Cl, C-H⋯S and π-π inter-actions [centroid-centroid distance = 3.6146 (19) Å], leading to the formation of a three-dimensional structure.

Improving yields by switching central metal ions in porphyrazine-catalyzed oxidation of glucose into value-added organic acids with SnO2 in aqueous solution.

Photocatalysis has exhibited huge potential in selective conversion of glucose into value-added chemicals. Therefore, modulation of photocatalytic material for selective upgrading of glucose is significant. Here, we have investigated the insertion of different central metal ions, Fe, Co, Mn, and Zn, into porphyrazine loading with SnO2 for access to more efficient transformation of glucose into value-added organic acids in aqueous solution at mild reaction conditions. The best selectivity for organic acids containing glucaric acid, gluconic acid, and formic acid of 85.9% at 41.2% glucose conversion was attained by using the SnO2/CoPz composite after reacting for 3 h. The effects of central metal ions on surficial potential and related possible factors have been studied. Experimental results showed that the introduction of metalloporphyrazine with different central metal ions on the surface of SnO2 has a significant effect on the separation of photogenerated charges, changing the adsorption and desorption of glucose and products on the catalyst surface. The central metal ions of cobalt and iron contributed more to the positive effects toward enhancing conversion of glucose and yields of products, and manganese and zinc contributed more to the negative effects, resulting in the poor yield of products. The differences from the central metals may attribute to the surficial potential change of the composite and the coordination effects between the metal and oxygen atom. An appropriate surficial potential environment of the photocatalyst may achieve a better interactive relationship between the catalyst and reactant, while appropriate ability of producing active species matched with adsorption and desorption abilities would gain a better yield of products. These results have provided valued ideas for designing more efficient photocatalysts in selective oxidation of glucose utilizing clean solar energy in the future.

Corrigendum: Improving yields by switching central metal ions in porphyrazine-catalyzed oxidation of glucose into value-added organic acids with SnO2 in aqueous solution.

[This corrects the article DOI: 10.3389/fchem.2023.1114454.].

Synthesis, structural characterization, photophysics, and broadband nonlinear absorption of a platinum(II) complex with the 6-(7-benzothiazol-2'-yl-9,9-diethyl-9 H-fluoren-2-yl)-2,2'-bipyridinyl ligand.

A platinum complex with the 6-(7-benzothiazol-2'-yl-9,9-diethyl-9H-fluoren-2-yl)-2,2'-bipyridinyl ligand (1) was synthesized and the crystal structure was determined. UV/Vis absorption, emission, and transient difference absorption of 1 were systematically investigated. DFT calculations were carried out on 1 to characterize the electronic ground state and aid in the understanding of the nature of low-lying excited electronic states. Complex 1 exhibits intense structured (1)π-π* absorption at λ(abs)<440 nm, and a broad, moderate (1)MLCT/(1)LLCT transition at 440-520 nm in CH(2)Cl(2) solution. A structured (3)π-π*/(3)MLCT emission at about 590 nm was observed at room temperature and at 77 K. Complex 1 exhibits both singlet and triplet excited-state absorption from 450 nm to 750 nm, which are tentatively attributed to the (1)π-π* and (3)π-π* excited states of the 6-(7-benzothiazol-2'-yl-9,9-diethyl-9H-fluoren-2-yl)-2,2'-bipyridine ligand, respectively. Z-scan experiments were conducted by using ns and ps pulses at 532 nm, and ps pulses at a variety of visible and near-IR wavelengths. The experimental data were fitted by a five-level model by using the excited-state parameters obtained from the photophysical study to deduce the effective singlet and triplet excited-state absorption cross sections in the visible spectral region and the effective two-photon absorption cross sections in the near-IR region. Our results demonstrate that 1 possesses large ratios of excited-state absorption cross sections relative to that of the ground-state in the visible spectral region; this results in a remarkable degree of reverse saturable absorption from 1 in CH(2)Cl(2) solution illuminated by ns laser pulses at 532 nm. The two-photon absorption cross sections in the near-IR region for 1 are among the largest values reported for platinum complexes. Therefore, 1 is an excellent, broadband, nonlinear absorbing material that exhibits strong reverse saturable absorption in the visible spectral region and large two-photon-assisted excited-state absorption in the near-IR region.

Bis(pyridine-2-carboxyl-ato-κ2 N,O)copper(II)]-benzene-1,3,5-tri-carb-oxy-lic acid-water (1/2/2).

In the title complex, [Cu(C6H4O2N)2]·2C9H6O6·2H2O, the Cu2+ ion lies on a center of inversion and coordinates with symmetry related pyridine nitro-gen and carboxyl oxygen atoms from two pyridine-2-carb-oxy-lic acid anions, giving rise to a square-planar coordination geometry. There are weak axial bonds between Cu and an O atom of a symmetry-related trimesic acid moieties [Cu⋯O = 2.837 (2) Å] The Cu⋯O weak inter-actions and hydrogen bonds stabilize the whole structure.

Excited-state absorption of a bipyridyl platinum(II) complex with alkynyl-benzothiazolylfluorene units.

The singlet excited-state lifetime of a bipyridyl platinum(II) complex containing two alkynyl-benzothiazolylfluorene units was determined to be 145+/-105 ps by fitting femtosecond transient difference absorption data, and the triplet quantum yield was measured to be 0.14. A ground-state absorption cross section of 6.1 x 10(-19) cm(2) at 532 nm was deduced from UV-visible absorption data. Excited-state absorption cross sections of (6.7+/-0.1) x 10(-17) cm(2) (singlet) and (4.6+/-0.1) x 10(-16) cm(2) (triplet) were obtained by using a five-level dynamic model to fit open-aperture Z scans at picosecond and nanosecond pulse widths and a variety of pulse energies. For this complex, the ratio of the triplet excited-state absorption cross section to the ground-state absorption cross section--long used as a figure of merit for reverse saturable absorbers--thus stands at 754, to our knowledge the largest ever reported at 532 nm wavelength.

Synthesis and photophysics of platinum(II) 6-phenyl-4-(9,9-dihexylfluoren-2-yl)-2,2'-bipyridine complexes with phenothiazinyl acetylide ligand.

Two platinum 6-phenyl-4-(9,9-dihexylfluoren-2-yl)-2,2'-bipyridine complexes (4 and 5) with phenothiazinyl acetylide ligand were synthesized and characterized. Their UV-vis absorption and emission characteristics in solution and in Langmuir-Blodgett (LB) film were systematically investigated. The triplet transient difference absorption and nonlinear absorption properties were also studied for these complexes. Both complexes exhibit a broad metal-to-ligand charge transfer/intraligand charge transfer/ligand-to-ligand charge transfer ((1)MLCT/(1)ILCT/(1)LLCT) absorption band between 400 and 500 nm and a (3)MLCT/(3)ILCT/(3)pi,pi* emission band at approximately 594 nm at room temperature, which blue shifts at 77 K. Both UV-vis absorption and emission spectra show negative solvatochromic effect. The triplet excited-state lifetime at room temperature for complex 4 is approximately 1.2 micros, which is longer than that for complex 5 (approximately 600 ns). The emission quantum yield of complex 4 in toluene is 0.18 and 0.053 for complex 5. Both of the complexes also exhibit broad and moderately strong triplet transient absorption from the near-UV to the near-IR spectral region. However, 5 exhibits stronger reverse-saturable absorption than complex 4 does at 532 nm for nanosecond laser pulses. This is attributed to the weaker ground-state absorption but stronger triplet excited-state absorption at 532 nm for 5 than for 4, which leads to a larger ratio of excited-state absorption cross section to ground-state absorption for 5 than 4. In addition, LB films of 4 and 5 were prepared and characterized by AFM technique. The UV-vis absorption and emission spectra of the LB films of 4 and 5 were also investigated and compared with those obtained in solution.

A highly sensitive and selective colorimetric probe based on a cycloruthenated complex: an Hg2+-promoted switch of thiophene coordination.

A cyclometalated ruthenium complex [Ru(pthb)(bpy)2]+ (1, bpy = 2,2'-bipyridine, Hpthb = 3,3-dimethyl-2-(5-pyridylthiophen-2-yl)vinyl-benzo[e]indolium-1-propylsulfonate) could be converted from a C-coordinated structure to non-metallated species with N,S-bonded Hpthb upon treatment with mercury(ii) ions in water. Strikingly, the switch in the coordination mode resulted in a great absorption change along with a change in the solution color of 1 from dark red to light yellow. Therefore, 1 can be used as a colorimetric probe to detect mercury(ii) ions by the naked eye. Although the emission was not observed for 1 in water, it still demonstrated an appreciably low detection limit of 21 nM by using UV-Vis absorption spectroscopy, which was comparable with those of some probes determined by ratiometric fluorescence spectroscopy.

Acid-sensitive Pt(II) 2,6-di(pyridin-2-yl)pyrimidin-4(1H)-one complexes.

Three Pt(II) 2,6-di(pyridin-2-yl)pyrimidin-4(1H)-one complexes (2-4) with chloride or 4-ethynyltolyl ancillary ligands were synthesized and characterized. The photophysical properties of 2-4 were investigated in different solvents and at different acid concentrations. Their electronic absorption and emission responses at various acid concentrations were compared to those of 5. 2-4 all exhibit a broad charge-transfer band in their electronic absorption spectra from 380 to 500 nm and emit at about 560 nm in acetonitrile at room temperature, presumably ascribed to the triplet metal-to-ligand charge transfer ((3)MLCT) state. All of them exhibit broad and relatively strong triplet transient absorption in the visible to the near-IR region (450-820 nm). Upon addition of p-toluenesulfonic acid, the original charge-transfer band intensity decreases, accompanied by the increase of the absorption in the 350-400 nm region in their electronic absorption spectra. Meanwhile, the (3)MLCT emission is quenched, and the triplet transient absorption intensity decreases. The changes in electronic absorption, emission, and the transient absorption spectra are reversible upon the addition of base, that is, triethylamine. The reversible acid sensitivity is caused by the protonation and deprotonation of the carbonyl oxygen on the terdentate ligand. Therefore, these platinum complexes could be potential chromogenic and luminescent sensors for acids.

Crystal structure of a heterometallic coordination polymer: catena-poly[[[tetra-aqua-cobalt(II)]-µ-pyridine-2,6-di-carboxyl-ato-calcium(II)-µ-pyridine-2,6-di-carboxyl-ato] dihydrate].

In the crystal of the title polymeric complex, {[CoCa(C7H3NO4)2(H2O)4]·2H2O} n (1), the CoII ion is N,O,O'-chelated by two pyridine-2,6-di-carboxyl-ate anions in a distorted N2O4 octa-hedral geometry, and two carboxyl-ate O atoms of pyridine-2,6-di-carboxyl-ate anions bridge tetra-aqua-calcium(II) units to form polymeric chains propagating along the b-axis direction. In the crystal, O-H⋯O and C-H⋯O hydrogen bonds, and offset π-π stacking inter-actions [inter-centroid distances = 3.551 (1) and 3.746 (1) Å] involving inversion-related pyridine rings link the polymeric chains and lattice water mol-ecules to form a supra-molecular three-dimensional framework.

Synergistic photocatalytic performance of cobalt tetra(2-hydroxymethyl-1,4-dithiin)porphyrazine loaded on zinc oxide nanoparticles.

A new ZnO/CoPz(hmdtn)4 composite as a highly efficient photocatalyst was successfully prepared by cobalt tetra(2-hydroxymethyl-1,4-dithiin)porphyrazine (CoPz(hmdtn)4) impregnated onto the surface of ZnO nanoparticles, the photocatalytic performance of ZnO/CoPz(hmdtn)4 under both simulated sunlight and visible light (λ ≥ 400 nm) irradiation was assessed by degradation of Rhodamine B (RhB) and phenol in aerated conditions. The ZnO/CoPz(hmdtn)4 manifested much higher photocatalytic activity than pure ZnO and pure CoPz(hmdtn)4, originating from the synergistic effect between CoPz(hmdtn)4 and ZnO. Furthermore, the XPS analysis revealed that there may be strong interaction between CoPz(hmdtn)4 and ZnO. Thereby ZnO/CoPz(hmdtn)4 with excellent stability can maintain high photocatalytic activity over five runs on the basis of the reusability test. The active species generated in the photocatalytic system were verified by electron spin resonance (ESR) technology. A possible mechanism of the synergistic effect between CoPz(hmdtn)4 and ZnO was also proposed.

Crystal structure of a heterometallic coordination polymer: poly[di-aqua-bis-(µ7-benzene-1,3,5-tri-carboxyl-ato)dicalcium(II)copper(II)].

In the title complex, [Ca2Cu(C9H3O6)2(H2O)2] n , the CaII and CuII cations are bridged by the benzene-1,3,5-tri-carboxyl-ate anions (BTC3-) to form the coordination polymer, in which each BTC3- anion bridges two CuII and five CaII cations with a µ7 coordination mode. The CuII cation, located at an inversion centre, is in a nearly square-planar geometry defined by four O atoms from four bridging BTC3- anions, while the CaII cation is in a distorted octa-hedral geometry defined by five O atoms from bridging BTC3- anions and one water mol-ecule. O-H⋯O hydrogen bonds between coordinating water mol-ecules and carboxyl groups further stabilize the structure; π-π stacking is also observed between parallel benzene rings, the centroid-to-centroid distance being 3.357 (2) Å.

Metal-Organic Frameworks Constructed from a New Thiophene-Functionalized Dicarboxylate: Luminescence Sensing and Pesticide Removal.

A family of thiophene-based metal-organic frameworks (MOFs), [Zn(L)(BBI)·(H2O)2] (1) (BBI = 1,1'-(1,4-butanediyl)bis(imidazole)) and [Cd(L)(TPOM)0.75]·xS (2) (TPOM = tetrakis(4-pyridyloxy-methylene) methane, S represents noncoordinated solvent molecules) was constructed by employing a new linear thiophene-functionalized dicarboxylic acid (benzo-(1,2;4,5)-bis(thiophene-2'-carboxylic acid, H2L) to assemble with d10 ions in the presence of a flexible ancillary ligand under solvothermal conditions, which exhibit diverse structures. Most strikingly, both compounds 1 and 2 could be efficient luminescent sensory materials that are highly selective and sensitive to environmental contaminants, especially for Hg(II), Cu(II), Cr(VI), and salicylaldehyde, and yet remain unaffected by other molecules that may coexit. Furthermore, this is the first report on MOF-based sensors capable of recyclable detection of Hg(II), Cr(VI), and salicylaldehyde so far. The luminescent sensing mechanism was studied in detail as well. In addition, compound 2 is one of the rare examples of high-performance MOFs trapping 2,4-dichlorophenol from the wasted methanol solution.

Naked-eye detection of fluoride ion in water: a remarkably selective easy-to-prepare test paper.

A test paper for high-selectivity detecting fluoride ion in natural aqueous environments without any spectroscopic instrumentation was achieved by using Ru-bipy based quinonehydrazone as a chromo- and fluorogenic hybrid chemosensor.

A novel pyramidal multiple alkali metal cluster [K3(H2O)]3+ stabilized within a capsule containing 16-nitrogen donors.

A novel multiple alkali metal cluster K3(H2O)]3+ interior within a high-symmetry cubic capsule containing 16-nitrogen donors is achieved via self-assembly from twenty components.

Imidazolidinium-based robust crypt with unique selectivity for fluoride anion.

A new imidazolidinium based receptor exhibiting unique affinity and high selectivity for fluoride anion through steric requirements and the cooperativity of multiple intramolecular binding, has been designed, synthesized and structurally characterized.

Extending the bandwidth of reverse saturable absorption in platinum complexes using two-photon-initiated excited-state absorption.

Pt(II) complexes bearing 4-(7-(benzothiazol-2'-yl)-9,9-diethylfluoren-2-yl)-2,2':6',2″-terpyridine or 4-(7-(benzothiazol-2'-yl)-9,9-diethylfluoren-2-yl)ethynyl-2,2':6',2″-terpyridine ligand exhibit strong reverse saturable absorption in the visible spectral region and large two-photon initiated excited-state absorption in the near-IR region. They are promising broadband nonlinear absorbing materials from the visible to the near-IR region. The extended π-conjugation in complex 2 that has a C≡C linker between the terpyridine ligand and the 4-(7-(benzothiazol-2'-yl)-9,9-diethylfluoren-2-yl) substituent significantly increases the two-photon absorption cross sections (σ(2)), making it among the strongest of two-photon absorbing Pt(II) complexes.

A new chiral N-heterocyclic carbene silver(I) cylinder: synthesis, crystal structure and catalytic properties.

A new chiral cyclic triimidazoline salt and its chiral N-heterocyclic carbene trisilver(I) cylinder-like cage was prepared via self-assembly, with size-selective catalytic performance for the cyanosilylation of several Schiff-base compounds.