A Kinetic Study of Phenolic Oxidation by H2O2 Using the Schiff Base Complexes As Mimetic Peroxidases

The Schiff base complexes containing a transition metal ion, Co^II and Cu^II, were used as mimetic peroxidase in the catalytic oxidation of phenol by H₂O₂. The characteristic spectra of the Schiff base complexes in H₂O₂-buffered solution were recorded and analyzed, respectively. The mechanism and the kinetic mathematic model of the phenol catalytic oxidation were studied. The results showed that the Schiff base complexes containing the transition metal ion, Co^II and Cu^II, as peroxidase mimics exhibited good catalytic activity and the character of the peroxidase in the catalytic oxidation of phenol by H₂O₂ under different conditions.     

Studies on the Phenol Oxidation by H2O2 Catalyzed by Metallomicelle Made from Crowned Schiff Base Co(II) Complexes Containing Benzoaza-15-crown-5

Three novel cobalt(II) complexes of the benzoaza-15-crown-5 Schiff base, CoL¹, CoL², and CoL³ were synthesized and characterized. Metallomicelles made from CoL and surfactants (CTAB, LSS, and Brij35) were used as mimetic peroxidase in the catalytic oxidation of phenol by H₂O₂. For comparison, the catalytic activity of the complexes (CoL¹, CoL², and CoL³) were also investigated. The mechanism and a kinetic mathematic model of the phenol catalytic oxidation were studied. The acid effect of reaction system, structural effect of the complexes, and effect of temperature on the rate of the phenol catalytic oxidation by the mimetic peroxidase were discussed. The results show that the Schiff base cobalt(II) complexes and their metallomicelles as peroxidase mimics exhibit good catalytic activity and similar catalytic character to natural enzyme.     

Studies on Phenol Oxidation with H2O2 Catalyzed by Schiff Base Cobalt(II) Complexes in Micellar Solution

The two Schiff base cobalt(II) complexes, CoL¹ and CoL², were synthesized and characterized. The metallomicelle made up of the cobalt(II) complexes and surfactants (CTAB, LSS and Brij35), as mimic peroxidase metalloenzyme, were used in the catalytic oxidation of phenol by H₂O₂. The mechanism and a kinetic mathematic model of the phenol catalytic oxidation were studied. The acid effect of reaction system, structural effect of the complexes, and effect of temperature on the rate of the phenol oxidation catalyzed by the mimetic peroxidases have been discussed. The results showed that the schiff base cobalt(II) complexes and their metallomicelles as peroxidase mimics exhibit good catalytic activity and similar catalytic character to natural enzyme.     

Mn(II) and VO(IV) Schiff base complexes encapsulated in nanocavities of zeolite-Y: catalytic activity toward oxidation of alkenes and reduction of aldehydes

Oxovanadium(IV) and manganese(II) complexes of two Schiff base ligands, bis(2,4-dihydroxyacetophenone)-1,2-propandiimine (H₂L₁) and bis(2,4-dihydroxyacetophenone)-ethylenediimine (H₂L₂) were synthesized and characterized. The encapsulation of these complexes in the nanocavities of zeolite-Y was achieved by a flexible ligand method. The prepared heterogeneous catalysts have been characterized by FTIR, NMR and atomic absorption spectroscopy, X-ray diffraction patterns, scanning electron microscopy and BET. The catalytic activities of the encapsulated complexes were studied in the oxidation of alkenes with H₂O₂ and the reduction of aldehydes with NaBH₄. In most cases, the manganese (II) complexes (MnL₁-Y, MnL₂-Y) showed better activity than the oxovanadium (IV) complexes (VOL₁-Y, VOL₂-Y) in both oxidation of alkenes and reduction of aldehydes. The catalytic activity of the recovered catalysts was compared with the fresh ones.     

PNPP Hydrolysis Catalyzed by Manganese(III) Complexes with Crowned Salicylaldimine Schiff Base Ligand

Four manganese(III) complexes (MnL¹Cl, MnL²Cl, MnL⁴₂Cl, MnL⁵₂Cl) with a crowned salicylaldimine Schiff base ligand have been synthesized and employed as models to mimic hydrolase in the hydrolysis of p-nitrophenyl picolinate (PNPP). The kinetics and mechanism of catalytic PNPP hydrolysis have been investigated. The kinetic mathematical model of PNPP cleavage catalyzed by these complexes has been proposed. The effects of the ligand structure and crown ether ring in complexes, and the reactive temperature on the rate of catalytic PNPP hydrolysis have been also examined. The results show that compared with the crown-free analogous MnL³Cl and MnL⁶₂Cl, the crowned Schiff base manganese(III) complexes, MnL¹Cl, MnL²Cl, MnL⁴₂Cl and MnL⁵₂Cl, exhibit more high catalytic activity, which follow the order: MnL¹Cl >MnL²Cl >MnL⁴₂Cl >MnL⁵₂Cl >MnL³Cl >MnL⁶₂Cl; the pseudo-first-order-rate (k_obs) for the PNPP hydrolysis catalyzed by the complex MnL¹Cl containing three crown ether rings is highest among six complexes and is 1.81 times that of MnL³Cl, 1.49 × 10³ times that of spontaneous hydrolysis of PNPP, respectively, at pH = 7.00, [S] = 2.0 × 10⁻⁴ mol dm⁻³.     

Catalytic epoxidation performance and dioxygen affinities of unsymmetrical Schiff base transition–metal complexes with pendant aza-crown or morpholino groups

Abstract  Unsymmetrical Schiff base Co^II complexes (CoL¹–CoL⁶) and Schiff base Mn^III complexes (MnL¹Cl–MnL⁶Cl) with pendant aza-crown or morpholino groups were synthesized according to the literature. The oxygen uptake of Schiff base Co^II complexes in MeOCH₂CH₂OMe solution was determined at different temperatures, and the equilibrium constants (KO₂) and thermodynamic parameters (∆H ⁰, ∆S ⁰) for oxygenation were calculated. The corresponding Mn^III complexes, MnL¹Cl–MnL⁶Cl, were employed to catalyze epoxidation of styrene at ambient temperature and pressures. The effects of crown ether on the modulation of O₂-binding capability and the catalytic oxidation of styrene are discussed. The results indicate that the dioxygen affinities of the Co^II complexes are much more enhanced by aza-crown pendant group than that by morpholino pendant group, and the O₂-binding capabilities of CoL¹–CoL³ with aza-crown pendant group can also be enhanced by adding alkali metal cations (Li⁺, Na⁺, and K⁺); similarly, the catalytic activities of the Mn^III complexes with aza-crown pendant group, MnL¹Cl–MnL³Cl, are higher than those of the Mn^III complexes with morpholino pendant group, MnL⁴Cl–MnL⁶Cl. Graphical abstracts   Catalytic epoxidation performance and dioxygen affinities of unsymmetrical Schiff base transition–metal complexes with pendant aza-crown or morpholino groups. Jian-zhang Li*, Bin Xu, Wei-dong Jiang Key Laboratory of Green and Technology, Department of Chemistry, Sichuan University of Science & Engineering, Zigong, Sichuan 643000, People’s Republic of China Bo Zhou, Wei Zeng, Sheng-ying Qin Department of Chemistry, Sichuan University, Chengdu, Sichuan 610064, People’s Republic of China The oxygen uptake of Schiff base Co^II complexes in MeOCH₂CH₂OMe solution was determined at different temperatures, and the equilibrium constants (KO₂) and thermodynamic parameters (∆H ⁰, ∆S ⁰) for oxygenation were calculated. The corresponding MnIII complexes, MnL¹Cl-MnL⁶Cl, were employed to catalyze epoxidation of styrene at ambient temperature and pressures. The effects of crown ether on the modulation of O₂-binding capability and the catalytic oxidation of styrene are discussed.     

A route to magnetically separable nanocatalysts: Combined experimental and theoretical investigation of alkyl substituent role in ligand backbone towards epoxidation ability

We have prepared two chiral Schiff base ligands, H₂L¹ and H₂L², and one achiral Schiff base ligand, H₂L³, by treating 2,6‐diformyl‐4‐methylphenol separately with (R )‐1,2‐diaminopropane, (R )‐1,2‐diaminocyclohexane and 1,1′‐dimethylethylenediamine, in ethanolic medium, respectively. The complexes MnL¹ClO₄ ( 1 ), MnL²ClO₄ ( 2 ), MnL³ClO₄ ( 3 ), FeL¹ClO₄ ( 4 ), FeL²ClO₄ ( 5 ) and FeL³ClO₄ ( 6 ) have been obtained by reacting the ligands H₂L¹, H₂L² and H₂L³ with manganese(III) perchlorate or iron(III) perchlorate in methanol. Circular dichroism studies suggest that ligands H₂L¹ and H₂L² and their corresponding complexes have asymmetric character. Complexes 1 – 6 have been used as homogeneous catalysts for epoxidation of alkenes. Manganese systems have been found to be much better than iron counterparts for alkene epoxidation, with 3 as the best catalyst among manganese systems and 6 as the best among iron systems. The order of their experimental catalytic efficiency has also been rationalized by theoretical calculations. We have observed higher enantiomeric excess product with catalysts 1 and 4 , so they were attached to surface‐modified magnetic nanoparticles to obtain two new magnetically separable nanocatalysts, Fe₃O₄@dopa@MnL¹ and Fe₃O₄@dopa@FeL⁴. They have been characterized and their alkene epoxidation ability has been investigated. These catalysts can be easily recovered by magnetic separation and recycled several times without significant loss of catalytic activity. Hence our study focuses on the synthesis of a magnetically recoverable asymmetric nanocatalyst that finds applications in epoxidation of alkenes and at the same time can be recycled and reused.     

Self-assembled biomimetic catalysts: studies of the catalase and peroxidase activities of Mn(III)-Schiff base complexes

Five Mn(III) nitrate complexes have been synthesized from dianionic hexadentate Schiff bases obtained by the condensation of 3-ethoxy-2-hydroxybenzaldehyde with different diamines. The complexes have been characterized by elemental analysis, ESI mass spectrometry, IR and ¹H NMR spectroscopy, r. t. magnetic, and molar conductivity measurements. Parallel-mode EPR spectroscopy of 1 is also reported. Ligand H₂L³ and complexes [MnL¹(H₂O)₂](NO₃)(CH₃OH) (1), [MnL³(H₂O)₂]₂(NO₃)₂(CH₃OH)(H₂O) (3), and [MnL⁴(H₂O)₂](NO₃)(H₂O)₂ (4) were crystallographically characterized. The X-ray structures show the self-assembly of the Mn(III)–Schiff base complexes through µ-aquo bridges between neighboring axial water molecules and also by π–π stacking interactions, establishing dimeric and polymeric structures. The peroxidase and catalase activities of the complexes have been studied. Complexes with the shorter spacer between the imine groups (1–2) behave as better peroxidase and catalase mimics, probably due to their ability to coordinate the hydrogen peroxide substrate to manganese.     

Reactivity of Schiff Base Manganese(III) Complexes with Different Pendants toward the Hydrolysis of p‐Nitrophenyl Picolinate

This paper describes the catalytic performance of two manganese(III) complexes with mono‐Schiff base ligands as artificial hydrolases towards the hydrolysis of p‐nitrophenyl picolinate (PNPP). Observations reveal that the one complex (MnL₂²Cl) containing morpholine pendants exhibits 1.2–1.7 fold kinetic advantage over the other one (MnL₂¹Cl) containing benzoaza‐15‐crown‐5 group. Especially, optimum molecule structures using a Gaussian 03 software confirm that MnL₂²Cl indeed possesses a relatively open linked site for the approaching of PNPP, resulting in higher efficiency due to a convenient association between substrate (PNPP) and MnL₂²Cl. In addition, the steric hindrance of two pendants, i.e., benzoaza‐15‐crown‐5 and morpholine, may be a main influencing factor for tuning catalytic activities of the synthesized Mn(III) catalysts. Both Mn(III) catalysts used here were found to have fine tolerance to the operated temperature and pH. Related kinetic and thermodynamic analyses were also given to demonstrate their structure‐activity relationships (SAR) of both catalysts used.     

Oxidation Reaction of Phenol with H2O2 Catalyzed by Metallomicelles Made of Co(II) and Cu(II) Complexes of Imidazole Groups and Micelle as Mimic Peroxidase

The imidazole derivatives (N,N‐bis(2‐ethyl‐5‐methyl‐imidazole‐4‐ylmethyl) amino‐propane (biap)) and its complexes containing cobalt or copper ion were synthesized in this study. The oxidation reaction of phenol with oxidant H₂O₂ catalyzed by the metallomicelle made of the complexes of imidazole groups and micelle (CTAB, Brij35, LSS) as the mimetic peroxidase was studied. The results show that the reaction rate for the catalytic oxidation of phenol increases by a factor of approximately 1×10⁵ in the metallomicelle over that in the simple micelles or the pure buffer solution at pH=6.9 and 25°C. The catalytic effects changed with H₂O₂, temperature, pH, and surfactant kind in the catalytic reactive process are discussed. A kinetic mathematic model of the phenol oxidation catalyzed by the metallomicelle is proposed.     

Studies on the Kinetics and Mechanism of Hydrolysis of p-nitrophenyl Picolinate (PNPP) by Unsymmetrical bis-Schiff Base Complexes with Aza-crown Ether or Morpholino Pendants

Two novel unsymmetrical bis-Schiff base manganese(III) and cobalt(II) complexes with benzo-10-aza-crown ether pendants (MnL¹Cl, CoL¹), and their analogoues with morpholino pendants (MnL²Cl, CoL²), have been synthesized and employed as models to mimic hydrolase in p-nitrophenyl picolinate (PNPP). The kinetics and the mechanism of PNPP hydrolysis catalyzed by these complexes were investigated. A kinetic mathematical model of PNPP cleavage catalyzed by these complexes was proposed. The effects of the complexes structure and reactive temperature on the rate of catalytic PNPP hydrolysis have been also examined. The results showed that the rate for the catalytic PNPP hydrolysis increased following the increase in pH of the buffer solution; four complexes exhibited high activity in the catalytic PNPP hydrolysis. Compared with the crown-free analogoues MnL²Cl and CoL², the crowned Schiff base complexes (MnL¹Cl, CoL¹) exhibit a higher catalytic activity; the pseudo-first-order-rate (k_obs) for the PNPP hydrolysis catalyzed by the complex MnL¹Cl containing benzo-10-aza-crown ether is 1.04 × 10³ that of spontaneous hydrolysis of PNPP at pH = 7.00, [S] = 2.0×10⁻⁴ mol dm⁻³.     

PNPP Cleavage Catalyzed by Schiff Base Mn(III) Complexes Containing Polyether Side Chains in CTAB Micellar Solutions

Two Schiff base Mn(III) complexes containing polyether side chain were synthesized and characterized. The catalytic hydrolysis of p‐nitrophenyl picolinate (PNPP) by the two complexes in the buffered CTAB micellar solution in the pH range of 6.60–8.20 was investigated kinetically in this study. The influences of acidity, temperature, and structure of complex on the catalytic cleavage of PNPP were also studied. The mechanism of PNPP hydrolysis catalyzed by Schiff base manganese(III) complexes in CTAB micellar solution was proposed. The relative kinetic and thermodynamic parameters were determined. Comparied with the pseudo‐first‐order rate constant (k ₀) of PNPP spontaneous hydrolysis in water, the pseudo‐first‐order rate constants (k _obsd) of PNPP catalytic hydrolysis are 1.93×10³ fold for MnL¹ ₂Cl and 1.06×10³ fold for MnL² ₂Cl in CTAB micellar solution at pH=7.00, T=25°C, and [S]=2.0×10^?4mol · dm^?3, respectively. Furthermore, comparing the k _obsd of PNPP catalytic hydrolysis by metallomicelles with that of PNPP hydrolysis catalyzed only by metal complexes or CTAB micelle at the above‐mentioned condition, metallomicelles of MnL₂(L=L¹, L²) Cl/CTAB exhibit notable catalytic activities for promoting PNPP hydrolysis, and MnL¹ ₂Cl/CTAB system is superior in promoting cleavage of PNPP relative to MnL² ₂Cl/CTAB system under the same experimental conditions. The results indicate that the rate of PNPP catalytic cleavage is influenced by the structures of the two complexes, the acidity of reaction systems, and the solubilization of PNPP in CTAB micelles.     

氮杂冠醚或吗啉基取代的单Schiff碱配合物催化α-吡啶甲酸对硝基苯酯水解

两种含5-取代苯并-10-氮杂-15-冠-5的Schiff碱锰(III)、钴(II)配合物( , )及其吗啉基取代的类似物( , ) 用于催化α-吡啶甲酸对硝基苯酯(PNPP)水解。探讨了氮杂冠醚Schiff 碱配合物催化PNPP水解的动力学和机理;提出了配合物催化PNPP水解的动力学模型;考察了配合物结构、反应温度、缓冲溶液pH值等对PNPP水解反应的影响。结果表明,在25℃条件下随着缓冲溶液pH值的增大,催化PNPP水解速率提高;含取代苯并-10-氮杂-15-冠-5的Schiff碱配合物表现出更高的催化活性。根据阿累尼乌斯公式和不同温度下的表观一级常数求出水解反应的表观活化能。     

p‐Nitrophenyl Picolinate Cleavage by Unsymmetrical Bis‐Schiff Base Manganese(III) and Cobalt(II) Complexes with Aza‐Crown Ether or Morpholino Pendants

The unsymmetrical bis‐Schiff base manganese(III) and cobalt(II) complexes with either benzo‐10‐aza‐crown ether pendants (MnL¹Cl, MnL²Cl) or morpholino pendant (MnL³Cl, CoL³) have been employed as models for hydrolase by studying the kinetics of their hydrolysis reactions with p‐nitrophenyl picolinate (PNPP). A kinetic model of PNPP cleavage catalyzed by these complexes is proposed. The effects of complex structures and reaction temperature on the rate of PNPP hydrolysis have been examined. All four complexes exhibit high catalytic activity and the rate increases with pH under 25°C. The complexes of ligands containing a crown ether group exhibit higher catalytic activities than the non‐crown analogues. The catalytic activity of the complexes follows the order Mn(III)>Co(II) under the same ligands.     

Zeolite-Y enslaved manganese(III) complexes as heterogeneous catalysts

Traditional catalytic procedures for oxidation of phenol produce environmentally undesirable wastes. As a consequence, there is a clear demand for development of an environmentally benign catalytic route for the selective oxidation of phenol. A series of zeolite-Y enslaved Mn(III) complexes with Schiff bases derived from vanillin furoic-2-carboxylic acid hydrazone (VFCH), vanillin thiophene-2-carboxylic acid hydrazone (VTCH), ethylvanillin thiophene-2-carboxylic acid hydrazone (EVTCH), and/or ethylvanillin furoic-2-carboxylic acid hydrazone have been synthesized and characterized by physico-chemical techniques. Catalytic oxidations of phenol using 30% H₂O₂ as an oxidant over [Mn(VTCH)₂·2H₂O]⁺-Y, [Mn(VFCH)₂·2H₂O]⁺-Y, and [Mn(EVTCH)₂·2H₂O]⁺-Y under mild conditions were studied. These zeolite-Y enslaved Mn(III) complexes are stable and recyclable under current reaction conditions.     

Studies on <Emphasis Type="Italic">p</Emphasis>-nitrophenyl picolinate cleavage by mono-Schiff base complexes with aza-crown ether or morpholino pendants

Abstract  Mono-Schiff base manganese(III) and cobalt(II) complexes with either benzo-10-aza-crown ether pendants (MnL¹ ₂ Cl, CoL¹ ₂) or morpholino pendants (MnL² ₂Cl, CoL² ₂) have been employed as models for hydrolase enzymes by studying the kinetics of their hydrolysis reactions with p-nitrophenyl picolinate (PNPP). A kinetic model of PNPP cleavage catalyzed by these complexes is proposed. The effects of complex structures and reaction temperature on the rate of catalytic PNPP hydrolysis have been also examined. The rate increases with pH of the buffer solution; all four complexes exhibited high activity in the catalytic PNPP hydrolysis. Compared with the crown-free analogues MnL² ₂Cl and CoL² ₂, the crowned Schiff base complexes (MnL¹ ₂Cl, CoL¹ ₂) exhibit higher catalytic activity. The pseudo-first-order-rate ( k _obs ) for the PNPP hydrolysis catalyzed by the complex MnL¹ ₂Cl containing benzo-10-aza-crown ether is 1.06 × 10³ times that of spontaneous hydrolysis of PNPP at pH = 7.00, 25 °C, [S] = 2.0 × 10⁻⁴ mol dm⁻³. Graphical Abstract   Studies on p-nitrophenyl picolinate cleavage by mono-Schiff base complexes with aza-crown ether or morpholino pendants Jian-zhang Li*, Fa-mei Feng, Bin Xu,Wei-dong Jiang Key Laboratory of Green and Technology, Department of Chemistry, Sichuan University of Science & Engineering, Zigong, Sichuan, 643000, P.R. China Sheng-ying Qin Department of Chemistry, Sichuan University, Chengdu, Sichuan, 610064, P.R. China Mono-Schiff base manganese(III) and cobalt(II) complexes with either benzo-10-aza-crown ether pendants (MnL¹ ₂Cl, CoL¹ ₂) or morpholino pendants (MnL² ₂Cl, CoL² ₂) have been employed as models for hydrolase enzymes by studying the kinetics of their hydrolysis reactions with PNPP. A kinetic model of PNPP cleavage catalyzed by these complexes is proposed. Compared with the crown-free analogy MnL² ₂Cl and CoL² ₂, the crowned Schiff base complexes (MnL¹ ₂Cl, CoL¹ ₂) exhibit higher catalytic activity.      

Antiozonant activity of the silica modified with 3d metal complexes

Criteria for preliminary selection of the antiozonants based on the silica modified with the complexes of 3d metal were proposed and the activity of the antiozonants as a dependence on the nature of the ligands (Schiff bases, Cl^?, NO ₃ ^? ) and metal ions [Cu(II), Co(II), Mn(II)] was established. We found that advantageous were complexes MnL₂/ $\overline {Si} $ , where L denotes a Schiff base of phenol or quinoline series, whose kinetic and specific stoichiometric energy parameters of the reaction were the largest because of the formation during the reaction of the manganese oxide form which performs the catalytic decomposition of ozone.     

Synthesis,structural characterization and catalytic activity study of Mn(II), Fe(III), Ni(II), Cu(II) and Zn(II) complexes of quinoxaline-2-carboxalidine-2-amino-5-methylphenol: Crystal structure of the nickel(II) complex

Five new transition metal complexes [MnL(OAc)]·H₂O (1), [FeLCl₂] (2), [NiL₂]·H₂O (3), [CuLCl] (4) and [ZnL₂]·2H₂O (5) have been synthesized using a tridentate Schiff base ligand, HL (quinoxaline-2-carboxalidine-2-amino-5-methylphenol) and the complexes have been characterized by physicochemical and spectroscopic techniques. The spectral analyses reveal an octahedral geometry for 3, square pyramidal structure for 2 and square planar structure for 4. Analytical and physicochemical data indicate tetrahedral structure for 1 and octahedral structure for 5. The crystallographic study reveals that [NiL₂]·H₂O shows distorted octahedral geometry with a cis arrangement of N₄O₂ donor set of the bis Schiff base and exhibits a two-dimensional polymeric structure parallel to [0 1 0] plane. The complexes were screened for catalytic phenol hydroxylation reaction. Coordinatively unsaturated manganese(II), iron(III) and copper(II) complexes were found to be active catalysts. The poor catalytic activity of the nickel(II) complex is due to coordinatively saturated octahedral nature of the complex. Maximum conversion of phenol was observed for the copper(II) complex and the major product was catechol.     

Supramolecular networks of Mn(III)-Schiff base complexes assembled by nitrate counterions: X-ray crystal structures of 1D chains and 2D networks

A series of Mn(III) nitrate complexes have been synthesized from dianionic hexadentate Schiff bases obtained by condensation of 3-methoxy-2-hydroxybenzaldehyde with different diamines. The complexes have been characterised by elemental analysis, ESI mass spectrometry, IR and ¹H NMR spectroscopy. Magnetic studies and molar conductivity measurements were also performed. Complexes [MnL¹(H₂O)₂]₂·2NO₃·2CH₃OH (1), [MnL²(H₂O)₂]₂·2NO₃·2CH₃OH (2) and [MnL⁵(H₂O)₂]₂·2NO₃·6H₂O (5) were crystallographically characterised. The X-ray structures show an octahedral geometry around the metal with the Schiff base in the equatorial plane acting as tetradentate and water or methanol molecules in the axial positions. The octahedron entities are linked in pairs by μ-aquo bridges between neighbouring axial water molecules and also by π-π stacking interactions, establishing dimeric and polymeric structures. Nitrate anions are accommodated in the cavities of the framework and form hydrogen bonds with the aqua ligands and the methanol or crystal water, leading to infinite supramolecular aggregates of the complexes. Comparison of chloride, perchlorate and nitrate complexes indicate that the nature of the anions is the key factor directing the structural topologies.     

Synthesis,crystal structures,and catalytic oxidation properties of oxidovanadium(V) complexes with Schiff base ligands

Two new Schiff base ligands 2-chloro-N′-(5-fluoro-2-hydroxybenzylidene)benzohydrazide (H₂L^a) and 4-fluoro-2-{[2-(2-hydroxyethylamino)ethylimino]methyl}phenol (HL^b) were synthesized and characterized. Their respective oxidovanadium complexes, [VOL^a(OMe)(MeOH)]·MeOH (1) and [VO(μ-O)L^b]₂ (2), were synthesized and characterized by spectroscopy and single-crystal X-ray diffraction. The coordination sphere of each V atom is octahedral. Both complexes showed selective heterogeneous catalytic properties with 74–98 % conversion, for the oxidation of cyclohexene, cyclopentene, and benzyl alcohol using H₂O₂ as primary oxidant.