Switching the Mechanism of NADH Photooxidation by Supramolecular Interactions

A series of three Ru(II) polypyridine complexes was investigated for the selective photocatalytic oxidation of NAD(P)H to NAD(P)⁺ in water. A combination of (time-resolved) spectroscopic studies and photocatalysis experiments revealed that ligand design can be used to control the mechanism of the photooxidation: For prototypical Ru(II) complexes a ¹O₂ pathway was found. Rudppz ([(tbbpy)₂Ru(dppz)]Cl₂, tbbpy=4,4'-di-tert-butyl-2,2'-bipyridine, dppz=dipyrido[3,2-a:2′,3′-c]phenazine), instead, initiated the cofactor oxidation by electron transfer from NAD(P)H enabled by supramolecular binding between substrate and catalyst. Expulsion of the photoproduct NAD(P)⁺ from the supramolecular binding site in Rudppz allowed very efficient turnover. Therefore, Rudppz permits repetitive selective assembly and oxidative conversion of reduced naturally occurring nicotinamides by recognizing the redox state of the cofactor under formation of H₂O₂ as additional product. This photocatalytic process can fuel discontinuous photobiocatalysis.     

Competition Between O2 and H2O2 in the Oxidation of Fe(II) in Natural Waters

The oxidation rates of nanomolar levels of Fe(II) in seawater (salinity S = 36.2) by mixtures of O₂ and H₂O₂ has been measured as a function of pH (5.8–8.4) and temperature (3–35∘C). A competition exists for the oxidation of Fe(II) in the presence of both O₂ (μ mol⋅L⁻¹ levels) and H₂O₂ (nmol⋅L⁻¹ levels). A kinetic model has been applied to explain the experimental results that considers the interactions of Fe(II) with the major ions in seawater. In the presence of both oxidants, the hydrolyzed Fe(II) species dominate the Fe(II) oxidation process between pH 6 and 8.5. Over pH range 6.2–7.9, the FeOH⁺ species are the most active, whereas above pH 7.9, the Fe(OH)⁰₂ species are the most active at the levels of CO²⁻₃ concentration present in seawater. The predicted Fe(II) oxidation rate at [Fe(II)]₀ = 30nmol⋅L⁻¹ and pH = 8.17 in the oxygen-saturated seawater with [H₂O₂]₀ = 50nmol⋅L⁻¹ (log ₁₀ k = −2.24s⁻¹) is in excellent agreement with the experimental value of log ₁₀ k = −2.29s⁻¹ ([H₂O₂]₀ = 55nmol⋅L⁻¹, pH = 8).     

[RuIII(EDTA)(H2O)]− catalyzed oxidation of biologically important thiols by H2O2

[Ru^III(EDTA)(H₂O)]^? (EDTA^4? = ethylenediaminetetraacetate) catalyzes the oxidation of biological thiols, RSH (RSH = cysteine, glutathione, N-acetylcysteine, penicillamine) using H₂O₂ as precursor oxidant. The kinetics of the oxidation process were studied spectrophotometrically as a function of [Ru^III(EDTA)(H₂O)]^?, [H₂O₂], [RSH], and pH (4–8). Spectral analyses and kinetic data are suggestive of a catalytic pathway in which the RSH reacts with [Ru^III(EDTA)] catalyst complex to form [Ru^III((EDTA)(SR)]^2? intermediate species. In the subsequent reaction step the oxidant, H₂O₂, reacts directly with the coordinated S of the [Ru^III((EDTA)(SR)]^2? intermediate leading to formation of the disulfido (RSSR) oxidation product (identified by HPLC and ESI-MS studies) of thiols (RSH). Based on the experimental results, a working mechanism involving oxo-transfer from H₂O₂ to the coordinated thiols is proposed for the catalytic oxidation.     

Kinetic Study of the Reduction of Bromate Ion by Tris(1,10-Phenanthroline)Iron(II) and Aquoiron(II) Ions — Implication for the Bromate-Gallic Acid Oscillating Reaction

The kinetics of the bromate oxidation of tris(1,10-phenanthroline)iron(II) (Fe(phen)₃²⁺) and aquoiron(II) (Fe²⁺ (aq)) have been studied in aqueous sulfuric acid solutions at μ = 1.0M and with Fe(II) complexes in great excess. The rate laws for both reactions generally can be described as -d [Fe(II)]/6dt = d[Br^?]/dt = k[Fe(II)] [BrO^?₃] for [H⁺]₀ = 0.428–1.00M. For [BrO^?₃]₀ = 1.00 × 10^?4M. [Fe²⁺]₀ = (0.724–1.45)x 10^?2 M, and [H⁺]₀ = 1.00M, k = 3.34 ± 0.37 M^?1s^?1 at 25°. For [BrO^?₃]₀ = (1.00–1.50) × 10^?4M, [Fe²⁺]₀ = 7.24 × 10^?3M ([phen]₀ = 0.0353M), and [H⁺]₀ = 1.00M, k = (4.40 ± 0.16) × 10^?2 M^?1s^?1 at 25°. Kinetic results suggest that the BrO^?₃-Fe²⁺ reaction proceeds by an inner-sphere mechanism while the BrO^?₃-Fe(phen)₃²⁺ reaction by a dissociative mechanism. The implication of these results for the bromate-gallic acid and other bromate oscillators is also presented.     

Insertion of Molecular Oxygen in Transition‐Metal Hydride Bonds,Oxygen‐Bond Activation,and Unimolecular Dissociation of Metal Hydroperoxide Intermediates. Short Communication

Thermal activation of molecular oxygen is observed for the late‐transition‐metal cationic complexes [M(H)(OH)]⁺ with M=Fe, Co, and Ni. Most of the reactions proceed via insertion in a metal? hydride bond followed by the dissociation of the resulting metal hydroperoxide intermediate(s) upon losses of O, OH, and H₂O. As indicated by labeling studies, the processes for the Ni complex are very specific such that the O‐atoms of the neutrals expelled originate almost exclusively from the substrate O₂. In comparison to the [M(H)(OH)]⁺ cations, the ion? molecule reactions of the metal hydride systems [MH]⁺ (M=Fe, Co, Ni, Pd, and Pt) with dioxygen are rather inefficient, if they occur at all. However, for the solvated complexes [M(H)(H₂O)]⁺ (M=Fe, Co, Ni), the reaction with O₂ involving O? O bond activation show higher reactivity depending on the transition metal: 60% for the Ni, 16% for the Co, and only 4% for the Fe complex relative to the [Ni(H)(OH)]⁺/O₂ couple.     

Ligand Exchange in Pd(II)-NaCl-H<Subscript>2</Subscript>O and Pd(II)-HCl-H<Subscript>2</Subscript>O Systems: Quantum-Chemical Consideration

The behavior of potassium tetrachloropalladate(II) in media simulating biological liquids is studied. The rate of aquation in aqueous NaCl solutions is shown to be higher than the rate at which the Cl^? ligand enters the inner coordination sphere of the Pd atom. In HCl solutions, the formation of the Pd chloro complexes predominates due to protonation of water molecules in the composition of aqua complexes. The reactions of replacement of the ligands (H₂O molecules and H₃O⁺ ion) in the planar Pd(II) complexes by the chloride ion are studied by the ZINDO/1 method. All the complexes containing H₂O and H₃O⁺ ligands, except for [Pd(H₂O)₄]²⁺, contain intramolecular hydrogen bonds. The ZINDO/1 and RHF/STO-6G(d) calculations revealed “nonclassic” symmetrical O? H?O hydrogen bond in the [[Pd(H₂O)₃(H₃O)]³⁺ and trans-[Pd(H₂O)₂(H₃O)Cl]²⁺ complexes. The replacement of the H₃O⁺ ion by the Cl^? ion at the first three steps is thermodynamically more advantageous than the displacement of water molecules from the metal coordination sphere. The logarithms of stepwise stability constants of Pd(II) chloro complexes are found to correlate linearly with the enthalpies (ZINDO/1, PM3) of reactions of H₂O replacement by Cl^?.     

Chemical and Photochemical Water Oxidation Catalyzed by Mononuclear Ruthenium Complexes with a Negatively Charged Tridentate Ligand

Two mononuclear ruthenium complexes [RuL(pic)₃] ( 1 ) and [RuL(bpy)(pic)] ( 2 ) (H₂L=2,6‐pyridinedicarboxylic acid, pic=4‐picoline, bpy=2,2′‐bipyridine) have been synthesized and fully characterized. Both complexes could promote water oxidation chemically and photochemically. Compared with other known ruthenium‐based water oxidation catalysts using [Ce(NH₄)₂(NO₃)₆] (Ce^IV) as the oxidant in solution at pH 1.0, complex 1 is one of the most active catalysts yet reported with an initial rate of 0.23 turnover s^?1. Under acidic conditions, the equatorial 4‐picoline in complex 1 dissociates first. In addition, ligand exchange in 1 occurs when the Ru^III state is reached. Based on the above observations and MS measurements of the intermediates during water oxidation by 1 using Ce^IV as oxidant, [RuL(pic)₂(H₂O)]⁺ is proposed as the real water oxidation catalyst.     

The Effect of Concentration Parameters on Complexation in the Iron(0)–Iron(II)–Glycine–Water System

The processes of formation of iron(II) complexes in aqueous glycine solutions in the pH range of 1.0–8.0 at 298 K and ionic strength of 1 mol/L (NaClO₄) are studied using Clark and Nikolskii’s oxidation potential method. The type and number of coordinated ligands, the nuclearity, and the total composition of the resulting complexes are determined. The following complex species are formed in the investigated system: [Fe(OH)(H₂O)₅]⁺, [FeHL(H₂O)₅]²⁺, [Fe(HL)(OH)(H₂O)₄]⁺, [Fe(OH)₂(H₂O)₄]⁰, [Fe₂(HL)₂(OH)₂(H₂O)₈]²⁺, and [Fe(HL)₂(H₂O)₄]²⁺. Their formation constants are calculated by the successive iterations method using Yusupov’s theoretical and experimental oxidation function. The model parameters of the resulting coordination compounds are determined.     

Structurally Modelling the 2-His-1-Carboxylate Facial Triad with a Bulky N,N,O Phenolate Ligand

We present the synthesis and coordination chemistry of a bulky, tripodal N,N,O ligand, Im^Ph2NNO ^{t Bu} ( L ), designed to model the 2-His-1-carboxylate facial triad (2H1C) by means of two imidazole groups and an anionic 2,4-di-tert-butyl-subtituted phenolate. Reacting K-L with MCl₂ (M = Fe, Zn) affords the isostructural, tetrahedral non-heme complexes [Fe(L)(Cl)] ( 1 ) and [Zn(L)(Cl)] ( 2 ) in high yield. The tridentate N,N,O ligand coordination observed in their X-ray crystal structures remains intact and well-defined in MeCN and CH₂Cl₂ solution. Reacting 2 with NaSPh affords a tetrahedral zinc thiolate complex, [Zn(L)(SPh)] ( 4 ), that is relevant to isopenicillin N synthase (IPNS) biomimicry. Cyclic voltammetry studies demonstrate the ligand's redox non-innocence, where phenolate oxidation is the first electrochemical response observed in K-L , 2 and 4 . However, the first electrochemical oxidation in 1 is iron-centred, the assignment of which is supported by DFT calculations. Overall, Im^Ph2NNO ^{t Bu} provides access to well-defined mononuclear, monoligated, N,N,O-bound metal complexes, enabling more accurate structural modelling of the 2H1C to be achieved.     

Phenol Oxidation by a Nickel(III)–Fluoride Complex: Exploring the Influence of the Proton Accepting Ligand in PCET Oxidation

In order to gain insight into the influence of the H⁺-accepting terminal ligand in high-valent oxidant mediated proton coupled electron transfer (PCET) reactions, the reactivity of a high valent nickel–fluoride complex [Ni^III(F)(L)] ( 2 , L=N,N’-(2,6-dimethylphenyl)-2,6-pyridinecarboxamidate) with substituted phenols was explored. Analysis of kinetic data from these reactions (Evans–Polanyi, Hammett, and Marcus plots, and KIE measurements) and the formed products show that 2 reacted with electron rich phenols through a hydrogen atom transfer (HAT, or concerted PCET) mechanism and with electron poor phenols through a stepwise proton transfer/electron transfer (PT/ET) reaction mechanism. The analogous complexes [Ni^III(Z)(L)] (Z=Cl, OCO₂H, O₂CCH₃, ONO₂) reacted with all phenols through a HAT mechanism. We explore the reason for a change in mechanism with the highly basic fluoride ligand in 2 . Complex 2 was also found to react one to two orders of magnitude faster than the corresponding analogous [Ni^III(Z)(L)] complexes. This was ascribed to a high bond dissociation free energy value associated with H−F (135 kcal mol⁻¹), which is postulated to be the product formed from PCET oxidation by 2 and is believed to be the driving force for the reaction. Our findings show that high-valent metal–fluoride complexes represent a class of highly reactive PCET oxidants.     

Effect of alkyl group on the structure of heterodinuclear Zn(II)–Cu(II) and Zn(II)–Ni(II) complexes derived from unsymmetrical phenol-based dicompartmental macro-acyclic ligands

A series of mono- and heterodinuclear macro-acyclic complexes of [ZnLCu(II)]²⁺ and [ZnLNi(II)]²⁺ were synthesized by a stepwise procedure. The phenol-based macro-acyclic dicompartmental ligands (L^2?) possess contagious hexadentate (N₄O₂) and tetradentate (N₂O₂) coordination sites, where in the mononuclear complexes [ZnL(H⁺)₂]²⁺ the latter site containing two alkyl-imine donor groups (ethyl or isopropyl) is attached to the azomethine moieties. The alkyl group(s) is eliminated upon introduction of the second metal (II) ion into N₂O₂ coordination site as a result of steric crowding of the alkyl groups along with the lack of flexibility associated with the imine groups. When the second metal ion is Cu(II) and R = isopropyl, the both of them are eliminated but when R = Et only one ethyl group is removed. However, in case of Ni(II) as the second metal ion, the both alkyl groups are eliminated regardless of the nature of the alkyl group. The origins of the structural variations are discussed. The prepared complexes were characterized by elemental analysis, molar conductance measurements, X-ray crystallography, IR, NMR and UV–Vis spectroscopies.     

Kinetics of hydrogen peroxide decomposition with complexed and “free” iron catalysts

The hydrogen peroxide decomposition kinetics were investigated for both “free” iron catalyst [Fe(II) and Fe(III)] and complexed iron catalyst [Fe(II) and Fe(III)] complexed with DTPA, EDTA, EGTA, and NTA as ligands (L). A kinetic model for free iron catalyst was derived assuming the formation of a reversible complex (Fe–HO₂), followed by an irreversible decomposition and using the pseudo‐steady‐state hypothesis (PSSH). This resulted in a first‐order rate at low H₂O₂ concentrations and a zero order rate at high H₂O₂ concentrations. The rate constants were determined using the method of initial rates of hydrogen peroxide decomposition. Complexed iron catalysts extend the region of significant activity to pH 2–10 vs. 2–4 for Fenton's reagent (free iron catalyst). A rate expression for Fe(III) complexes was derived using a mechanism similar to that of free iron, except that a L–Fe–HO₂ complex was reversibly formed, and subsequently decayed irreversibly into products. The pH plays a major role in the decomposition rate and was incorporated into the rate law by considering the metal complex specie, that is, EDTA–Fe–H, EDTA–Fe–(H₂O), EDTA–Fe–(OH), or EDTA–Fe–(OH)₂, as a separate complex with its unique kinetic coefficients. A model was then developed to describe the decomposition of H₂O₂ from pH 2–10 (initial rates = 1 × 10⁻⁴ to 1 × 10⁻⁷ M/s). In the neutral pH range (pH 6–9), the complexed iron catalyzed reactions still exhibited significant rates of reaction. At low pH, the Fe(II) was mostly uncomplexed and in the free form. The rate constants for the Fe(III)–L complexes are strongly dependent on the stability constant, K_ML, for the Fe(III)–L complex. The rates of reaction were in descending order NTA > EGTA > EDTA > DTPA, which are consistent with the respective log K_MLs for the Fe(III) complexes. Because the method of initial rates was used, the mechanism does not include the subsequent reactions, which may occur. For the complexed iron systems, the peroxide also attacks the chelating agent and by‐product‐complexing reactions occur. Accordingly, the model is valid only in the initial stages of reaction for the complexed system. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 24–35, 2000     

A mass spectrometry and DFT study of pyrithione complexes with transition metals in the gas phase

2‐Mercaptopyridine N ‐oxide (pyrithione, PTOH) along with several transition metal ions forms coordination compounds displaying notable biological activities. Gas‐phase complexes formed between pyrithione and manganese (II), cobalt (II), nickel (II), copper (II), and zinc (II) were investigated by infusion in the electrospray source of a quadrupole‐time of flight mass spectrometer. Remarkably, positive ion mode spectra displayed the singly charged metal adduct ion [C₁₀H₈MN₂O₂S₂]²⁺ ([M(PTO)₂]^+• or [M(DPTO)]^+•), where DPTO is dipyrithione, 2,2′‐dithiobis(pyridine N ‐oxide), among the most abundant peaks, implying a change in the oxidation state of whether the metal ion or the ligands. In addition, doubly charged ions were recognized as metal adduct ions containing DPTO ligands, [M(DPTO)_n]²⁺. Generation of [M(PTO)₂]^+• / [M(DPTO)]^+• could be traced by CID of [M(DPTO)₂]²⁺, by observation of the sequential losses of a charged (PTO⁺) and a radical (PTO^•) deprotonated pyrithione ligand. The fragmentation pathways of [M(PTO)₂]^+• / [M(DPTO)]^+• were compared among the different metal ions, and some common features were noticed. Density functional theory (DFT) calculations were employed to study the structures of the observed adduct ions, and especially, to decide in the adduct ion [M(PTO)₂]^+• / [M(DPTO)]^+• whether the ligands are 2 deprotonated pyrithiones or a single dipyrithione as well as the oxidation state of the metal ion in the complex. Characterization of gas‐phase pyrithione metal ion complexes becomes important, especially taking into account the presence of a redox‐active ligand in the complexes, because redox state changes that produce new species can have a marked effect on the overall toxicological/biological response elicited by the metal system.     

Direct Hydroxylation of Benzene with Hydrogen Peroxide Using Fe Complexes Encapsulated into Mesoporous Y-Type Zeolite

Mesoporous Y-type zeolite (MYZ) was prepared by an acid and base treatment of commercial Y-type zeolite (YZ). The mesopore volume of MYZ was six times higher than that of YZ. [Fe(terpy)₂]²⁺ complexes encapsulated into MYZ and YZ with different Fe contents (Fe(X)L-MYZ and Fe(X)L-YZ; X is the amount of Fe) were prepared and characterized. The oxidation of benzene with H₂O₂ using Fe(X)L-MYZ and Fe(X)L-YZ catalysts was carried out; phenol was selectively produced with all Fe-containing zeolite catalysts. As a result, the oxidation activity of benzene increased with increasing iron complex content in the Fe(X)L-MYZ and Fe(X)L-YZ catalysts. The oxidation activity of benzene using Fe(X)L-MYZ catalyst was higher than that using Fe(X)L-YZ. Furthermore, adding mesopores increased the catalytic activity of the iron complex as the iron complex content increased.     

Studies on synthesis,determination of CMC values,kinetics and the mechanism of iron(II) reduction of surfactant–Co(III)–ethylenediamine complexes in aqueous acid medium

The surfactant–Co(III) complexes of the type cis-[Co(en)₂AX]²⁺ (A?=?Tetradecylamine, X?=?Cl^?,?Br^?) were synthesised from corresponding dihalogeno complexes by the ligand substitution method. The critical micelle concentration (CMC) values of these surfactant complexes in aqueous solution were obtained from conductance measurements. The kinetics and mechanism of iron(II) reduction of surfactant–Co(III) complexes, cis-[Co(en)₂(C₁₄H₂₉NH₂)Cl](ClO₄)₂ and cis-[Co(en)₂(C₁₄H₂₉NH₂)Br] (ClO₄)₂ ions were studied spectrophotometrically in an aqueous acid medium by following the disappearance of Co(III) using an excess of the reductant under pseudo-first-order conditions: [Fe(II)]?=?0.25?mol?dm^?3, [H⁺]?=?0.1?mol?dm^?3, [μ]?=?1.0?mol?dm^?3 ionic strength in a nitrogen atmosphere at 303, 308 and 313?K. The reaction was found to be of second order and showed acid independence in the range [H⁺]?=?0.05–0.25?mol?dm^?3. The second-order rate constant increased with surfactant–Co(III) concentration and the presence of aggregation of the complex itself altered the reaction rate. The effects of [Fe(II)], [H⁺] and [μ] on the rate were determined. Activation and thermodynamic parameters were computed. It is suggested that the reaction of [Fe(II)] with Co(III) complex proceeds by an inner-sphere mechanism.     

Zero-Order Catalysis in TAML-Catalyzed Oxidation of Imidacloprid,a Neonicotinoid Pesticide

Bis-sulfonamide bis-amide TAML activator [Fe{4-NO₂C₆H₃-1,2-(NCOCMe₂NSO₂)₂CHMe}]⁻ ( 2 ) catalyzes oxidative degradation of the oxidation-resistant neonicotinoid insecticide, imidacloprid (IMI), by H₂O₂ at pH 7 and 25 °C, whereas the tetrakis-amide TAML [Fe{4-NO₂C₆H₃-1,2-(NCOCMe₂NCO)₂CF₂}]⁻ ( 1 ), previously regarded as the most catalytically active TAML, is inactive under the same conditions. At ultra-low concentrations of both imidacloprid and 2 , 62 % of the insecticide was oxidized in 2 h, at which time the catalyst is inactivated; oxidation resumes on addition of a succeeding aliquot of 2 . Acetate and oxamate were detected by ion chromatography, suggesting deep oxidation of imidacloprid. Explored at concentrations [ 2 ]≥[IMI], the reaction kinetics revealed unusually low kinetic order in 2 (0.164±0.006), which is observed alongside the first order in imidacloprid and an ascending hyperbolic dependence in [H₂O₂]. Actual independence of the reaction rate on the catalyst concentration is accounted for in terms of a reversible noncovalent binding between a substrate and a catalyst, which usually results in substrate inhibition when [catalyst]≪[substrate] but explains the zero order in the catalyst when [ 2 ]>[IMI]. A plausible mechanism of the TAML-catalyzed oxidations of imidacloprid is briefly discussed. Similar zero-order catalysis is presented for the oxidation of 3-methyl-4-nitrophenol by H₂O₂, catalyzed by the TAML analogue of 1 without a NO₂-group in the aromatic ring.     

Low‐dimensional coordination polymeric structures in alkali metal complex salts of the herbicide (2,4‐dichlorophenoxy)acetic acid (2,4‐D)

The Li, Rb and Cs complexes with the herbicide (2,4‐dichlorophenoxy)acetic acid (2,4‐D), namely poly[[aqua[μ₃‐(2,4‐dichlorophenoxy)acetato‐κ³O¹:O¹:O^1′]lithium(I)] dihydrate], {[Li(C₈H₅Cl₂O₃)(H₂O)]·2H₂O}_n, (I), poly[μ‐aqua‐bis[μ₃‐(2,4‐dichlorophenoxy)acetato‐κ⁴O¹:O^1′:O^1′,Cl²]dirubidium(I)], [Rb₂(C₈H₅Cl₂O₃)₂(H₂O)]_n, (II), and poly[μ‐aqua‐bis[μ₃‐(2,4‐dichlorophenoxy)acetato‐κ⁵O¹:O^1′:O^1′,O²,Cl²]dicaesium(I)], [Cs₂(C₈H₅Cl₂O₃)₂(H₂O)]_n, (III), respectively, have been determined and their two‐dimensional polymeric structures are described. In (I), the slightly distorted tetrahedral LiO₄ coordination involves three carboxylate O‐atom donors, of which two are bridging, and a monodentate aqua ligand, together with two water molecules of solvation. Conjoined six‐membered ring systems generate a one‐dimensional coordination polymeric chain which extends along b and interspecies water O—H...O hydrogen‐bonding interactions give the overall two‐dimensional layers which lie parallel to (001). In hemihydrate complex (II), the irregular octahedral RbO₅Cl coordination about Rb⁺ comprises a single bridging water molecule which lies on a twofold rotation axis, a bidentate O_carboxy,Cl‐chelate interaction and three bridging carboxylate O‐atom bonding interactions from the 2,4‐D ligand. A two‐dimensional coordination polymeric layer structure lying parallel to (100) is formed through a number of conjoined cyclic bridges, including a centrosymmetric four‐membered Rb₂O₂ ring system with an Rb...Rb separation of 4.3312 (5) Å. The coordinated water molecule forms intralayer aqua–carboxylate O—H...O hydrogen bonds. Complex (III) comprises two crystallographically independent (Z′ = 2) irregular CsO₆Cl coordination centres, each comprising two O‐atom donors (carboxylate and phenoxy) and a ring‐substituted Cl‐atom donor from the 2,4‐D ligand species in a tridentate chelate mode, two O‐atom donors from bridging carboxylate groups and one from a bridging water molecule. However, the two 2,4‐D ligands are conformationally very dissimilar, with one phenoxyacetate side chain being synclinal and the other being antiperiplanar. The minimum Cs...Cs separation is 4.4463 (5) Å. Structure extension gives coordination polymeric layers which lie parallel to (001) and are stabilized by intralayer water–carboxylate O—H...O hydrogen bonds.     

Copper(II), nickel(II), palladium(II) and iron(III) complexes of 2-(3-phthalhydrazidylazo)-1,3-diketones

Neutral complexes of three phthalhydrazidylazo-1,3-diketones [phthalhydrazidylazo-acetylacetone (H₂PAA),-benzoylacetone (H₂PBA) and-dibenzoylmethane (H₂PDM)] with Cu(II), Ni(II), Pd(II) and Fe(III) have been synthesised and characterized on the basis of their analytical data, magnetic moment, molar conductance and IR and¹H NMR spectral data. Dibasic tridentate coordination of the ligands is brought out by the above spectral data. Half-wave potentials and far IR spectral data of the Cu(II) complexes indicate that the H₂PAA complex is the most stable. M?ssbauer spectra of the Fe(III) complexes reveal that delocalisation of the metald electrons with the chelate ring decreases with increasing capability of the pendant groups of the ring for cross conjugation.     

More crystal field theory in action: the metal–4‐picoline (pic)–sulfate [M(pic)x]SO4 complexes (M = Fe,Co, Ni,Cu, Zn,and Cd)

Seven crystal structures of five first‐row (Fe, Co, Ni, Cu, and Zn) and one second‐row (Cd) transition metal–4‐picoline (pic)–sulfate complexes of the form [M(pic)_x]SO₄ are reported. These complexes are catena‐poly[[tetrakis(4‐methylpyridine‐κN)metal(II)]‐μ‐sulfato‐κ²O:O′], [M(SO₄)(C₆H₇N)₄]_n, where the metal/M is iron, cobalt, nickel, and cadmium, di‐μ‐sulfato‐κ⁴O:O‐bis[tris(4‐methylpyridine‐κN)copper(II)], [Cu₂(SO₄)₂(C₆H₇N)₆], catena‐poly[[bis(4‐methylpyridine‐κN)zinc(II)]‐μ‐sulfato‐κ²O:O′], [Zn(SO₄)(C₆H₇N)₂]_n, and catena‐poly[[tris(4‐methylpyridine‐κN)zinc(II)]‐μ‐sulfato‐κ²O:O′], [Zn(SO₄)(C₆H₇N)₃]_n. The Fe, Co, Ni, and Cd compounds are isomorphous, displaying polymeric crystal structures with infinite chains of M^II ions adopting an octahedral N₄O₂ coordination environment that involves four picoline ligands and two bridging sulfate anions. The Cu compound features a dimeric crystal structure, with the Cu^II ions possessing square‐pyramidal N₃O₂ coordination environments that contain three picoline ligands and two bridging sulfate anions. Zinc crystallizes in two forms, one exhibiting a polymeric crystal structure with infinite chains of Zn^II ions adopting a tetrahedral N₂O₂ coordination containing two picoline ligands and two bridging sulfate anions, and the other exhibiting a polymeric crystal structure with infinite chains of Zn^II ions adopting a trigonal bipyramidal N₃O₂ coordination containing three picoline ligands and two bridging sulfate anions. The structures are compared with the analogous pyridine complexes, and the observed coordination environments are examined in relation to crystal field theory.     

Spectral,magnetic and thermal studies on homometallic and heterometallic complexes of piperanol thiosemicarbazone

Piperanol thiosemicarbazone (HL) has been interacted with Ag⁺, Co(II), Ni(II) or Cu(II) binary to produce [Ag(HL)]EtOH · NO₃, [Ag₂(L)(H₂O)₂]NO₃, [Co(L)₃], [Cu(L)(H₂O)₃(OAc)]H₂O or [Ni(L)₂] and template with Ag⁺ to form [Cu₂Ag₂(L)₂(OH)₂(H₂O)₄]NO₃ and [NiAg(L)₂(H₂O)₂]NO₃. The prepared complexes are characterized by microanalysis, thermal, magnetic and spectral (IR, ¹H NMR, ESR and electronic) studies. Ag⁺ plays an important role in the complex formation. The variation in coordination may be due to the presence of two different metal ions and the preparation conditions. The outside nitrate is investigated by IR spectra. The outer sphere solvents are detected by IR and thermal analysis. Ni(II) complexes are found diamagnetic having a square-planar geometry. Cu(II) is reduced by the ligand to Cu(I). The cobalt complex is found diamagnetic confirming an air oxidation of Co(II) to Co(III) having a low spin octahedral geometry. The ligand and its metal complexes are found reducing agents which decolorized KMnO₄ solution in 2N H₂SO₄. CoNS and NiNS are the residual parts in the thermal decomposition of [Co(L)₃] and [Ni(L)₂].