Synthesis,characterization, and catalysis of recyclable new piperazine-bridged Mo(VI) polymers [MoO2(Salen)(piperazine)]n in highly selective oxygenation of alkenes and sulfides

This study reports synthesis and characterization of polymeric [MoO₂(Salen)] complexes that combine MoO₂(acac)₂ and polymeric ligands bearing N₂O₂ coordination sites, abbreviated herein as [piperazinCH₂{MoO₂(Salen)}]_n (6), [piperazinCH₂{MoO₂(Salophen)}]_n (7), and [piperazinCH₂{MoO₂(Salpn)}]_n (8). The epoxidation of alkenes using tert-butyl hydroperoxide and oxidation of sulfides to sulfoxides by urea hydrogen peroxide were enhanced with excellent selectivity under the catalytic influence of these coordination polymers. No relevant difference in activity was found due to change in the diamine in the Schiff’s base ligands. The stability of polymeric catalysts was assessed by recycling a sample five times in small batch reactions in both epoxidation and sulfoxidation. In the case of cyclooctene epoxidation, catalytic activity of [piperazinCH₂{MoO₂(Salen)}]_n increased without losing the selectivity, whereas the catalytic activity and selectivity of the spent catalyst decreased in sulfoxidation of methyl phenyl sulfide in consecutive runs. Loss of Mo from the coordination polymer has been investigated using the filtrates as potential catalysts in sulfoxidation reactions. Molybdenum leaching degree decreases through five cycles. Moreover, the catalyst can be recovered from the reaction mixture unchanged as determined by IR and UV–Vis spectra.     

Heterogeneous catalytic oxidation of chromotrope 2B with H2O2 and metal complexes supported on aluminum oxide hydroxide as catalyst

The heterogeneous catalytic oxidation of Chromotrope 2B (C2B) dye with H₂O₂ and the aluminum oxide hydroxide (AlOOH) modified with ammonia complexes of Cu^II, Co^II, Ni^II, and Cr^III (AlOOH/[Mⁿ⁺(amm)_m]) as catalysts were studied. The AlOOH/[Cu^II(amm)₄] is the most efficient catalyst and therefore it was chosen as the potential catalyst for the oxidative degradation of C2B in an aqueous solution. The AlOOH/[Cu^II(amm)₄] was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and transmission electron microscopy (TEM), techniques. The rate of reaction was dependent on the type of the metal complex supported on the AlOOH, initial concentration of the dye and H₂O₂, catalyst dose, pH, the concentration of NaCl, and temperature. The catalytic activity of the AlOOH/[Mⁿ⁺(amm)_m] according to the kind of metal ion decreased in the order: Cu^II > Co^II > Cr^III > Ni^II. Other catalysts consisting of the AlOOH supported with Cu^II complexed with ethylenediamine, ethanolamine, 1,3 propanediamine, and 1,4 butanediamine, (AlOOH/[Cu^II(amine)_m]), were also investigated. The activity of the (AlOOH/[Cu^II(amine)_m]) as catalyst according to the type of ligand followed the order: 1,4 butanediamine > 1,3 propanediamine > ethanolamine > ethylenediamine > ammonia. The reaction rate increased with increasing the catalyst dose, concentration of H₂O_2, C2B, and NaCl, pH, and temperature. Since the reusability results for the AlOOH/[Cu^II(amm)₄] revealed good stability over seven cycles, it can thus be considered a promising and cost-effective catalyst for the removal of harmful dyes from wastewater.     

Alkene and alkyne insertion into the Ir-H bond: Synthesis of new mono- and dinuclear alkyl and alkenyl iridium-pybox complexes

The treatment of the complex [Ir(η²-C₂H₄)₂(L)][PF₆] (L = κ³-N,N,N-(S,S)-ⁱPr-pybox) with acetic acid (1:1 molar ratio) at −10 °C affords the complex [Ir(C₂H₅)(κ²-O,O-O₂CCH₃)(L)][PF₆] (1). The dinuclear iridium(III) complex [Ir₂(μ-Cl)₂(C₂H₅)₂(L)₂][PF₆]₂ (2) is stereoselectively obtained by spontaneous intramolecular insertion of ethylene into the iridium-hydride bond of the mononuclear complex [IrClH(η²-C₂H₄)(L)][PF₆]. The single bridging chloride dinuclear derivative [Ir₂(μ-Cl)(C₂H₅)₂Cl₂(L)₂][PF₆] (3) is prepared by reaction of 2 with one equivalent of NaCl. The intramolecular insertion reaction of methyl and ethyl propiolate into the Ir-H bond of the complex [IrClH(MeCN)(L)][PF₆] gives stereoselectively the dinuclear complexes [Ir₂(μ-Cl)₂(HCCHCO₂R)₂(L)₂][PF₆]₂ (R = Me (4), Et (5)). The reaction of the complexes 4, 5 with one equivalent of NaCl or with an excess of sodium acetate yields the dinuclear [Ir₂(μ-Cl)(HCCHCO₂R)₂Cl₂(L)₂][PF₆] (R = Me (6), Et (7)) or the mononuclear [IrCl(HCCHCO₂Et)(κ¹-O-O₂CMe)(L)] (8) complexes, respectively. The structure of the dinuclear complex 3 · CH₂Cl₂ has been determined by an X-ray monocrystal study.     

Multistep oligometal complexation of the macrocyclic tris(N2O2) hexaoxime ligand

A macrocyclic oxime ligand H₆L, which has an O₆ cavity surrounded by three N₂O₂ chelate sites, was synthesized and the multistep oligometal complexation behavior was investigated. Upon complexation with zinc(II), the H₆L ligand afforded two kinds of hexanuclear complexes, L₂Zn₆ then LZn₆. Each of the complexation steps proceeded highly efficiently. In the latter complex, a Zn₃(μ₃‐OH) unit was incorporated into the trimetalated ligand, LZn₃. The integrated N₂O₂ chelate coordination sites provide a unique environment for a homometallic complex. The different nature of the peripheral N₂O₂ sites and the central O₆ site is particularly suitable for the selective formation of heterometallic complexes. Complexation with the zinc(II) ion in the presence of alkaline earth (Ca and Ba) or rare earth (La, Eu, Lu) metal ions afforded the heterotetranuclear complexes LZn₃M (M=Ca, Ba, La, Eu, Lu), in which zinc(II) and ion M occupied the N₂O₂ and O₆ sites, respectively. Titration experiments showed that the heterometallic complexes LZn₃Ca and LZn₃Ba were converted into the homometallic complex LZn₆ whereas LZn₃La was not. As a result, the binding affinity in the central O₆ site of the LZn₃ unit is apparently in the order of Ca²⁺, Ba²⁺3(μ₃‐OH)3+. This difference in the affinities of metal ions as well as the ionic sizes makes the novel conversion efficient, particularly in the case of the three‐step conversion from H₆L to H₂LZn₂Ba, LZn₃Ba, then LZn₆.     

Synthesis,Structure and Characterization of Dinuclear Pentacoordinate Molybdenum(V) Complexes with Thiosemicarbazone Ligands

New dinuclear pentacoordinate molybdenum(V) complexes, [Mo₂^VO₃L₂] [L = thiosemicarbazonato ligand: C₆H₄(O)CH:NN:C(S)NHR′ and C₁₀H₆(O)CH:NN:C(S)NHR′; R′ = H, CH₃, C₆H₅) were obtained either by oxygen atom abstraction from Mo^VIO₂L with triphenylphosphine or by using [Mo₂O₃(acac)₄] in the reaction with the corresponding ligands H₂L. Crystal and molecular structure of [Mo₂O₃{C₆H₄(O)CH:NN:C(S)NHC₆H₅}₂] · CH₃CN has been determined by the single‐crystal X‐ray diffraction method.     

A Robust One‐Compartment Fuel Cell with a Polynuclear Cyanide Complex as a Cathode for Utilizing H2O2 as a Sustainable Fuel at Ambient Conditions

A robust one‐compartment H₂O₂ fuel cell, which operates without membranes at room temperature, has been constructed by using a series of polynuclear cyanide complexes that contain Fe, Co, Mn, and Cr as cathodes, in sharp contrast to conventional H₂ and MeOH fuel cells, which require membranes and high temperatures. A high open‐circuit potential of 0.68 V was achieved by using Fe₃[{Co^III(CN)₆}₂] on a carbon cloth as the cathode and a Ni mesh as the anode of a H₂O₂ fuel cell by using an aqueous solution of H₂O₂ (0.30 M , pH 3) with a maximum power density of 0.45 mW cm^?2. The open‐circuit potential and maximum power density of the H₂O₂ fuel cell were further increased to 0.78 V and 1.2 mW cm^?2, respectively, by operation under these conditions at pH 1. No catalytic activity of Co₃[{Co^III(CN)₆}₂] and Co₃[{Fe^III(CN)₆}₂] towards H₂O₂ reduction suggests that the N‐bound Fe ions are active species for H₂O₂ reduction. H₂O₂ fuel cells that used Fe₃[{Mn^III(CN)₆}₂] and Fe₃[{Cr^III(CN)₆}₂] as the cathode exhibited lower performance compared with that using Fe₃[{Co^III(CN)₆}₂] as a cathode, because ligand isomerization of Fe₃[{M^III(CN)₆}₂] into (FeM₂)[{Fe^II(CN)₆}₂] (M=Cr or Mn) occurred to form inactive Fe? C bonds under ambient conditions, whereas no ligand isomerization of Fe₃[{Co^III(CN)₆}₂] occurred under the same reaction conditions. The importance of stable Fe²⁺? N bonds was further indicated by the high performance of the H₂O₂ fuel cells with Fe₃[{Ir^III(CN)₆}₂] and Fe₃[{Rh^III(CN)₆}₂], which also contained stable Fe²⁺? N bonds. The stable Fe²⁺? N bonds in Fe₃[{Co^III(CN)₆}₂], which lead to high activity for the electrocatalytic reduction of H₂O₂, allow Fe₃[{Co^III(CN)₆}₂] to act as a superior cathode in one‐compartment H₂O₂ fuel cells.     

A series of Salen-type homodinuclear lanthanide complexes and their slow magnetic relaxation in Dy2 and Ho2

A series of homodinuclear lanthanide complexes, namely, [Ln₂(L)₂(MeOH)₂(NO₃)₂] [Ln = Gd ( 1 ), Tb ( 2 ), Dy ( 3 ), and Ho ( 4 )], were synthesized by the reaction of Salen-type ligand, namely N, N′-bis(5-bromosalicylidene)ethane-1,2-diamine (H₂L), with lanthanide salts in methanol and acetonitrile solution. The two Ln^III ions in 1 – 4 are linked by two O_phenoxo atoms of two L²⁻ ligands to build a dinuclear skeleton. The eight-coordinate Ln^III center adopts a triangular dodecahedron geometry of D_2d symmetry. Theoretical calculations revealed that antiferromagnetic interactions exist in those complexes. Dynamic magnetic properties studies indicate that the Dy₂ complex behaves as a single-molecule magnet with an anisotropy barrier of U_eff ≈ 47.68 K and a pre-exponential factor τ₀ = 3.17 × 10⁻⁶ s under a zero applied field, whereas the Ho₂ complex exhibits a fast tunneling relaxation process that is rationalized through ab initio calculations.     

Molecular Design of Polyoxometalate-Based Compounds for Environmentally-Friendly Functional Group Transformations: From Molecular Catalysts to Heterogeneous Catalysts

This review article summarizes our recent researches for molecular design of polyoxometalates (POMs) and their related compounds for environmentally-friendly functional group transformations. The divacant POM [γ-SiW₁₀O₃₄(H₂O)₂]⁴⁻ exhibits high catalytic performance for mono-oxygenation-type reactions including epoxidation of olefins and allylic alcohols, sulfoxidation, and hydroxylation of organosilanes with H₂O₂. We have successfully synthesized several POM-based molecular catalysts (metal-substituted POMs) with controlled active sites by the introduction of metal species into the divacant POM as a “structural motif”. These molecular catalysts can efficiently activate H₂O₂ (vanadium-substituted POM for epoxidation) and alkynes (copper-substituted POM for click reaction and oxidative homocoupling of alkynes). The aluminum-substituted POM exhibits Lewis acidic catalysis for diastereoselective cyclization of (+)-citronellal to (−)-isopulegol. In addition, we have developed POM-based “molecular heterogeneous catalysts” by the “solidification” and “immobilization” of catalytically active POMs.     

Two 2D Polyoxometalate-Based Metal-Organic Complexes Constructed from a New Flexible N-Donor Ligand with High Capacitance Performances and Low Detection Limits of Cr(VI)

By designing and using a new flexible bis(pyrimidine)-bis(amide) ligand H₂L [H₂L=N,N′-bis(4-pyrimidinecarboxamido)-1,3-propane], two new polyoxometalate (POM)-based metal-organic complexes (MOCs), H₃[Cu₂(L)₂(PMo₁₂O₄₀)] ( 1 ) and [Cu₂(H₂L)₂(β-Mo₈O₂₆)] ( 2 ), were synthesized under solvothermal and hydrothermal conditions, respectively. In complexes 1 and 2 , metal-organic units and POM anions are linked together to form two distinct 2D structures. The [PMo₁₂O₄₀]³⁻ (PMo₁₂) anions were used as μ₄-bridging ligands in complex 1 and linked the 1D [Cu(L)]_n metal-organic chains to form a 2D layered structure. The [β-Mo₈O₂₆]⁴⁻ (Mo₈) anions adopted two diverse coordination modes in complex 2 and connected the 1D [Cu(H₂L)]_n²ⁿ⁺ metal-organic chains to generate a 2D grid structure. Complexes 1 – 2 can serve as electrode materials of supercapacitor and show large specific capacitances, up to 1065 and 956 F g⁻¹ at current density of 2 A g⁻¹, respectively, which surpass the parent POM and most of the previous reported POM-based electrode materials, thus demonstrating the important role of introducing metal-organic units in improving capacitive performances. Besides, the electrocatalytic redox activities of complexes 1 – 2 were also studied, both of them can be used as electrochemical sensors to detect Cr(VI) ions. They possess high sensitivity of 0.537 and 0.455 μA μM⁻¹ and low detection limits of 0.16 and 0.33 μM, which are below the maximum content of Cr(VI) in groundwater required by the WHO.     

New Rhenium(V) Nitrofuryl Semicarbazone Complexes.Crystal Structure of [ReOCl2(PPh3)(3‐(5‐Nitrofuryl)acroleine semicarbazone)]

The synthesis and characterization of the first two Re complexes with semicarbazone ligands is presented. Selected ligands are 5‐Nitro‐2‐furaldehyde semicarbazone (Nitrofurazone) ( L1 ) and its derivative 3‐(5‐Nitrofuryl)acroleine semicarbazone ( L2 ). Complexes of general formula [Re^VOCl₂(PPh₃) L ], where L = L1 and L2 , were prepared in good yields and high purity by reaction of [Re^VOCl₃(PPh₃)₂] with L in ethanol or methanol solutions. The complexes formula and molecular structures were supported by elemental analyses and electronic, FTIR, ¹H, ¹³C and ³¹P NMR spectroscopies. In addition, the crystal and molecular structure of [Re^VOCl₂(PPh₃) L2 ] was determined by X‐ray diffraction methods. [ReOCl₂(PPh₃)(3‐(5‐Nitrofuryl)acroleine semicarbazone)] crystallizes in the space group P‐1 with a = 11.2334(2), b = 11.3040(2), c = 12.5040(2) Å, α = 81.861(1), β = 63.555(1), γ = 83.626(1)°, and Z = 2. The Re(V) ion is in a distorted octahedral environment, equatorially coordinated to a deprotonated semicarbazone molecule acting as a bidentate ligand through its carbonylic oxygen and azomethynic nitrogen atoms, to an oxo ligand and a chlorine atom. The six‐fold coordination is completed by another chlorine atom and a triphenylphosphine ligand at the axial positions.     

Photochemistry of macromolecular metal complexes. II. Synthesis,thermal, and photochemistry of some polypyridyl complexes of chromium (III) bound to macromolecules

Polymer coordinated chromium(III) complexes [Cr(bpy)₂(PAA)₂]⁺, 1 , [Cr(bpy)₂-(PMA)₂]⁺, 2 , [Cr(phen)₂(PAA)₂]⁺, 3 , and [Cr(phen)₂(PMA)₂]⁺, 4 , [where bpy, phen, PAA and PMA are, respectively, 2,2′-bipyridine, 1,10-phenanthroline, poly(acrylic acid), and poly(methacrylic acid)] were synthesized. The polymer–chromium(III) complexes were characterized by elemental and spectroscopic analyses. Thermal substitution reactions of these macromolecular chromium(III) complexes in basic solutions lead to the replacement of the polypyridyl ligand by hydroxide ion while in strong acidic solutions the polymer complexes precipitate out. The photochemical reactions are qualitatively similar to that of the thermal reactions and the quantum yields are dependant on the pH of the medium. Further, lower quantum yields were observed for the aquation of the polymer complexes in comparison with the monomeric chromium(III) complexes and the results are discussed in terms of the effect of the polymer environment. Flash photolysis of 1 and 3 results in the formation of transients with maxima at 480 nm for 1 and 470 nm, 580 nm for 3 . The decay of the transients were found to obey first order kinetics and the rate constants were determined. The transients were suggested to be the alkyl-chromium complexes. Flash photolysis of 2 and 4 does not produce transients which is interpreted to be due to the presence of a methyl group in the ligand which hinders the formation of the carbonchromium bond.     

Effects of metal centers of complexes supported by S,S′-bis(2-pyridylmethyl)-1,2-thioethane on catalytic activities for electrochemical- and photochemical-driven hydrogen production

S,S′-bis(2-pyridylmethyl)-1,2-thioethane (bpte) reacts with MCl₂ (M = Co, Ni, and Fe) to give three complexes, namely, [Co^II(bpte)Cl₂] ( 1 ), [Ni^II(bpte)Cl₂] ( 2 ), and [Fe^II(bpte)Cl₂] ( 3 ), respectively. They all act as catalysts for proton or water reduction to dihydrogen via electrolysis or photolysis. Under an overpotential of 837.6 mV, the electrolysis of a neutral buffer with complex 1 , 2 , or 3 can provide 418 (±3), 555 (±3), and 243 (±3) moles of hydrogen per mole of catalyst per hour (mol H₂/mol catalyst/h), respectively. Under blue light, together with a photosensitizer and ascorbic acid (H₂A) as a sacrificial electron donor, the photolysis of an aqueous solution (pH 4.5) containing complex 1 , 2 , or 3 can afford 9060 (±5), 24,900 (±5), and 10,630 (±5) moles H₂ per mole of catalyst (mol of H₂ [mol of cat]⁻¹) during 83-h irradiation with an average apparent quantum yield of 7.1%, 24%, and 10%, respectively. The results show that the nickel complex [Ni^II(bpte)Cl₂] exhibits a more efficient activity for hydrogen generation than the iron or cobalt species. These findings may offer a new chemical paradigm for the design of efficient catalysts.     

Synthesis,Structure and Reactivity of [1, 2‐Bis(diphenylphosphinite)ethane]bromotricarbonylmanganese(I) with Reactions of Phosphites,Phosphonites. and Phosphinites

The manganese carbonyl complex [MnBr(CO)₃ L ] ( 1 ), where L = Ph₂POCH₂CH₂OPPh₂, was prepared by reacting [MnBr(CO)₅] with the bidentate ligand 1, 2‐Bis(diphenylphosphinite)ethane. From this compound and the appropriate phosphite, phosphinite or phosphonite ligands were synthesized the complexes [MnBr(CO)₂ LL ′], where L ′ = P(OMe)₃ ( 2 ) or P(OEt)₃ ( 3 ) and [MnBr(CO)₃ L ′₂], where L ′ =PPh(OEt)₂ ( 4 ) or PPh₂(OEt) ( 5 ). The obtained compounds have been characterized by elemental analysis, mass spectrometry, IR and NMR (¹H, ¹³C and ³¹P) spectroscopies and X‐ray diffractometry for the complexes 1 , 4 and 5 .     

New Mixed Ligand Copper(II) Complexes: Syntheses and Crystal Structures of Cu(Imid)2(H2O)L with Imid = Imidazole,L = Succinic and Fumaric Anions

Reactions of freshly prepared Cu(OH)_2—2x(CO₃)_x · yH₂O and imidazole (Imid) with succinic acid and fumaric acid, respectively, in CH₃OH/H₂O yields Cu(Imid)₂(H₂O)L with L = (C₄H₄O₄)^2— ( 1 ) and (C₄H₂O₄)^2— ( 2 ). Both isostructural complexes consist of 1D [Cu(Imid)₂(H₂O)L_2/2] polymeric chains, in which the T‐shaped [Cu(Imid)₂(H₂O)]²⁺ moieties are bridged by bis‐monodentate dicarboxylato ligands. Through the interchain hydrogen bonds between the coordinating H₂O molecule and the non‐coordinating carboxylate O atom, the polymeric chains are assembled into 2D layers, which are further assembled via interlayer N—H···O hydrogen bonds between imidazole N atom and the coordinating carboxylato O atom. Thermal analyses of 1 under N₂ stream showed that dehydration is immediately followed by decomposition of the anhydrous “Cu(Imid)₂(C₄H₄O₄)” intermediate into imidazole and “Cu(C₄H₄O₄)”. Upon further heating, sublimation of imidazole is followed by dissociation of the resulting “Cu(C₄H₄O₄)” into CO, CO₂, C₂H₄ in gaseous phase and solid CuO as residue. Crystal data: ( 1 ) C2/c (no. 15), a = 13.712(2), b = 5.589(1), c = 17.517(2)Å, β = 105.76(1)°, U = 1292.0(3)ų, Z = 4; ( 2 ) C2/c (no. 15), a = 13.758(2), b = 5.501(1), c = 17.464(2)Å, β = 106.05(2)°, U = 1270.2(3)ų, Z = 4.     

Synthesis and characterization of (pyrazolylethylphosphinite)nickel(II) complexes and catalytic activity towards ethylene oligomerization

Compounds (2‐(3,5‐dimethyl‐1H‐pyrazol‐1‐yl)ethyldiphenylphosphinite ( L1 ), 2‐(3,5‐di‐tert‐butyl‐1H‐pyrazol‐1‐yl)ethyldiphenylphosphinite ( L2 ) , and 2‐(3,5‐diphenyl‐1H‐pyrazol‐1‐yl)ethyldiphenylphosphinite ( L3 ) were prepared using the synthetic routes reported in literature. These compounds were reacted with [NiCl₂(DME)₂] or [NiBr₂(DME)₂] under appropriate reaction conditions to afford six new nickel(II) compounds ([NiCl₂( L1)] ( 1 ), [NiCl₂( L2 )] ( 2 ), [NiCl₂( L3 )] ( 3 ), [NiBr₂( L1 )] ( 4 ), [NiBr₂( L2 )] ( 5 ) and [NiBr₂( L3 )] ( 6 )). The new nickel(II) pre‐catalysts catalyze the oligomerization of ethylene, in the presence of ethylaluminium dichloride as co‐catalyst, to produce butenes, hexenes, octenes and higher carbon chain ethylene oligomers with very little Friedel‐Crafts alkylation products when the reactions were run in toluene.     

Darstellung und Struktur der Zweikernigen tert-Butyliminovanadium(IV)-Komplexe [(μ?NtC4H9)2V2(CH2CMe3)2X2] (X = OtC4H9, CH2CMe3)

Synthesis and Molecular Structure of the Binuclear tert-Butyliminovanadium(IV) Complexes [(μ-N^tC₄H₉)₂V₂(CH₂CMe₃)₂X₂] (X = O^tC₄H₉, CH₂CMe₃) Syntheses of the neopentylvanadium(V) compounds ^tC₄H₉N?V(CH₂CMe₃)_3?n(O^tC₄H₉)_n (n = 0 ( 7 ), 1 ( 6 ), 2) are described. 6 and 7 decompose by irradiation splitting off neopentane and yielding the binuclear diamagnetic neopentylvanadium(IV) complexes [(μ-N^tC₄H₉)₂V₂(CH₂CMe₃)₂X₂] [X = O^tC₄H₉ ( 8 ), CH₂CMe₃ ( 11 )]. All compounds obtained are characterized by ¹H and ⁵¹V NMR spectroscopy. 8 has been found by X-ray diffraction analysis to be a binuclear complex with bridging tert-butylimino ligands and a vanadium—vanadium single bond. The complexes ^tC₄H₉N?V(CH₂C₆H₅)(O^tC₄H₉)₂ and [(μ-N^tC₄H₉)₂V₂(CH₂SiMe₃)₂(O^tC₄H₉)₂] ( 10 ) have been also prepared; the crystal structure of 8 and 10 are nearly identical.     

Dinuclear Zn(II) and tetranuclear Co(II) complexes of a tetradentate N2O2 Schiff base ligand: Synthesis,crystal structure,characterization, DFT studies,cytotoxicity evaluation,and catalytic activity toward benzyl alcohol oxidation

Two novel dinuclear Zn(II) and tetranuclear Co(II) complexes of a tetradentate N₂O₂ Schiff base ligand (H₂ L = N,N′-bis-(4-hydroxysalicylidene)-1,3-diaminopropane) were prepared. The structures of the H₂ L ligand, [4(Zn₂ L (μ-O₂CCH₃)(O₂CCH₃)(H₂O))]⋅4CH₃OH⋅3H₂O (complex 1 ) and [Co₄ L ₂(μ-O₂CCH₃)₂(O₂CCH₃)₂]⋅2H₂O (complex 2 ) were unambiguously characterized by elemental analysis, mass spectrometry, Fourier-transform infrared spectroscopy (FT-IR), ¹H nuclear magnetic resonance (NMR), and UV–Vis spectroscopy. Single crystal X-ray diffraction studies revealed that two Zn(II) nuclei of 1 were connected through μ-phenolato and μ-acetato bridges and had distorted square pyramidal and distorted octahedral coordination geometries. Four Co(II) nuclei of 2 , on the contrary, showed a Co₄O₄ cubane-like configuration in which Co(II) cations and O atoms were located at alternating corners of a distorted cube. Density functional theory studies at the B3LYP/6–31 G(d) level were carried out to gain an insight into the thermodynamic stability of the complexes. in vitro cytotoxicity of the ligand and the complexes were evaluated using the MTT assay against breast cancer MCF7 cells, melanoma cancer A375 cells, and prostate cancer PC3 cells as representative human cancer cell lines. Complex 1 showed a remarkable activity against A375 and PC3 cancer cell lines. In addition, 1 and 2 were used as precursors to produce zinc and cobalt oxide nanoparticles via pyrolysis technique. The resulting ZnO and Co₃O₄ nanoparticles were characterized using FT-IR spectroscopy, UV–Vis diffuse reflectance spectroscopy, powder X-ray diffraction, and field emission scanning electron microscopy. Then, these nanoparticles were used as heterogeneous catalysts in the oxidation of benzyl alcohol with hydrogen peroxide at room temperature. Both catalysts showed good recyclability with a negligible decrease in their efficiency during four catalytic cycles. The results of theoretical calculations showed that the most stable product was benzaldehyde, which is in good agreement with the obtained experimental results.     

Cyclodextrin-supported Co(OH)2 Clusters as Electrocatalysts for Efficient and Selective H2O2 Synthesis

Co-based material catalysts have shown attractive application prospects in the 2 e⁻ oxygen reduction reaction (ORR). However, for the industrial synthesis of H₂O₂, there is still lack of Co-based catalysts with high production yield rate. Here, novel cyclodextrin-supported Co(OH)₂ cluster catalysts were prepared via a mild and facile method. The catalyst exhibited remarkable H₂O₂ selectivity (94.2 % ~ 98.2 %), good stability (99 % activity retention after 35 h), and ultra-high H₂O₂ production yield rate (5.58 mol g_catalyst⁻¹ h⁻¹ in the H-type electrolytic cell), demonstrating its promising industrial application potential. Density functional theory (DFT) reveals that the cyclodextrin-mediated Co(OH)₂ electronic structure optimizes the adsorption of OOH* intermediates and significantly enhances the activation energy barrier for dissociation, leading to the high reactivity and selectivity for the 2 e⁻ ORR. This work offers a valuable and practical strategy to design Co-based electrocatalysts for H₂O₂ production.     

Synthesis and magnetic properties of μ-phenolato copper (Ⅱ) binuclear complexes with different exogenous bridges

The syntheses and magnetic properties are reported for a series of copper(Ⅱ) complexes prepared from a pentadentate binucleating ligand 2,6-diformyl-4-methylphenol di(benzoyl-hydrazone) (H3L). These complexes incorporate different exogenous ions (X-) into a bridging position to form copper(Ⅱ) binuclear complexes of the formula [Cu2(H2L)X]2+, where X-= Br-(1), Cl-(2), HO-(3), C2H5O-(4) and C3H3N2- (5). The complexes have been characterized with variable temperature magnetic susceptibility (4.2-300 K) and the observed data were fit to those from a modified Bleaney-Bowers equation by least-squares method, giving the exchange integral 2J = -6.2 cm-1 for 1, -76.4 cm-1 for 2, -241.9 cm-1 for 3, -231.1 cm-1 for 4 and -343.8 cm-1 for 5. This suggested that there is an antiferromagnetic interaction between the Cu(Ⅱ) ions and the sequence of the effect of some exogenous bridging ligands on magnetic coupling is corresponding to that in spectrochemical series.