Solvatochromism and piezochromism of pentacyanoferrates(II) and of mixed valence iron(II)—iron(III) and ruthenium(II)—ruthenium(III) species

Pressure effects on the MLCT bands of the pyrazine- and 4-cyanopyridine-pentacyanoferrate(II) anions have been established. The relation of these piezochromic effects to the solvatochromism of each complex is put into the correlation between these parameters developed for other d⁶ ternary complexes. The conformance of piezochromic and solvatochromic efrects on MMCT bands for diiron and diruthenium mixed valence complexes to this correlation is examined.     

π Back-bonding of iron(II) complexes supported by tris(pyrid-2-ylmethyl)amine and its nitro-substituted derivatives

The electronic and geometric structures of a series of iron(II) complexes supported by tetradentate tris(pyrid-2-ylmethyl)amine-type ligands with different numbers of 4-nitropyridine groups, [(PyCH(2))(3-n)(4-NO(2)PyCH(2))(n)N] (n = 0-3), were examined by X-ray absorption fine-structure and variable-temperature (1)H NMR spectroscopies and theoretical calculations to reveal how the low-spin state is stabilized through π back-bonding interactions between iron(II) and 4-nitropyridine donor group(s).     

Micellar and Mixed-Micellar Effects on Alkaline Hydrolysis of tris(1,10–phenanthroline)iron(II): Kinetic Exploration

The kinetics of alkaline hydrolysis of tris(1,10–phenanthroline)iron(II) has been studied in the presence of nonionic and mixed nonionic–ionic micellar media at 308 K. The effects of mixed-micellar environments of nonionic with ionic surfactants (C₁₂E₂₃/ATABs and C₁₂E₂₃/SDS) on the hydrolytic rate have been studied. The rate decreases monotonically with an increment of [C₁₂E₂₃]_T (total Brij 35 concentration) at constant [^?OH]₀ and has been discussed with the pseudo-phase micellar model. The rate also decreases with [C₁₂E₂₃]_T at a continuous addition of ionic surfactants (ATABs and SDS). The observed rate constant k_obs follows the empirical relation: k_obs = (k₀ + θK [C₁₂E₂₃]_T)/(1 + K [C₁₂E₂₃]_T) (where θ and K are empirical constants). The values of θ remain unaffected, whereas K decreases nonlinearly with [ATABs]_T in a mixed C₁₂E₂₃?ATAB micellar system. But the k_obs in a mixed C₁₂E₂₃–SDS micellar system is much lower than that of the C₁₂E₂₃–ATAB system and do not comply with any micellar kinetic models.     

Interaction between chiral ions: synthesis and characterization of tartratovanadates(V) with tris(2,2′-bipyridine) complexes of iron(II) and nickel(II) as cations

Four new compounds composed of chiral complex cations and anions: Δ-[Fe(bpy)₃] Λ-[Fe(bpy)₃][V₄O₈((2R,3R)-tart)₂]·12H₂O (1), Δ-[Fe(bpy)₃]₂Λ-[Fe(bpy)₃]₂[V₄O₈((2R,3R)-tart)₂][V₄O₈((2S,3S)-tart)₂]·24H₂O (2), Δ-[Ni(bpy)₃]Λ-[Ni(bpy)₃][V₄O₈((2R,3R)-tart)₂]·12H₂O (3) and Δ-[Ni(bpy)₃]₂Λ-[Ni(bpy)₃]₂[V₄O₈((2R,3R)-tart)₂][V₄O₈((2S,3S)-tart)₂]·24H₂O (4) have been prepared. The compounds have been characterized by spectral methods, and their thermal decomposition was studied by simultaneous DTA, TG measurements. The final products after dynamic decomposition and additional heating were Fe₂V₄O₁₃ for 1 and 2 and Ni(VO₃)₂ for 3 and 4. The crystal structures determined for 1, 2 and 4 have evidenced that 1 is “hemiracemic” and 2 and 4 are “fully racemic” compounds.     

Synthesis and characterization of sterically encumbered β-ketoiminate complexes of iron(II) and zinc(II)

The synthesis, structure, and spectroscopic signatures of a series of four-coordinate iron(II) complexes of β-ketoiminates and their zinc(II) analogues are presented. An unusual five-coordinate iron(II) triflate with three oxygen bound protonated β-ketoimines is also synthesized and structurally characterized. Single-crystal X-ray crystallographic analysis reveals that the deprotonated bis(chelate)metal complexes are four-coordinate with various degrees of distortion depending on the degree of steric bulk and the electronics of the metal center. Each of the high-spin iron(II) centers exhibits multiple electronic transitions including ligand π to π*, metal-to-ligand charge transfer, and spin-forbidden d-d bands. The (1)H NMR spectra of the paramagnetic high-spin iron(II) centers are assigned on the basis of chemical shifts, longitudinal relaxation times (T(1)), relative integrations, and substitution of the ligands. The electrochemical studies support variations in the ligand strength. Parallel mode EPR measurements for the isopropyl substituted ligand complex of iron(II) show low-field resonances (g > 9.5) indicative of complex aggregation or crystallite formation. No suitable solvent system or glassing mixture was found to remedy this phenomenon. However, the bulkier diisopropylphenyl substituted ligand exhibits an integer spin signal consistent with an isolated iron(ii) center [S = 2; D = -7.1 ± 0.8 cm(-1); E/D = 0.1]. A tentative molecular orbital diagram is assembled.     

Mixed-ligand complexes of iron(II), iron(III), copper(II), and cobalt(II) with pyrazolonic and 2,2′-bipyridine ligands

New mixed-ligand complexes, [M₂(BAMP)(bipy)₂][MCl₄]₂, M=Co⁺²(1), Cu⁺²(2), [M₂(TAMEN)(bipy)₂][MCl₄]₂, M=Fe⁺²(3), Co²⁺(4), and [Fe₂(TAMEN)(bipy)₂][FeCl₆]₂ (5), where BAMP and TAMEN stand for the Mannich bases N,N′-bis(antipyryl-4-methylene)-piperazine and N,N′-tetra(antipyryl-4-methylene)-1,2-ethane-diamine, respectively, have been obtained and characterized by elemental analyses, conductometric and magnetic susceptibility measurements at room temperature, mass spectrometry, UV-Vis, infrared, and mass spectroscopy, and ¹H NMR spectra for the ligands.     

Electrochemistry of microparticles of tris (2,2′-bipyridine) ruthenium(II) hexafluorophosphate

The electrochemical behaviour of tris(2,2′-bipyridine)ruthenium(II) hexafluorophosphate (Ru(II)) microparticles, immobilised on a graphite electrode and adjacent to an aqueous electrolyte solution, has been studied by cyclic voltammetry and an in situ spectroelectrochemical technique. The solid Ru(II) complex exhibits one reversible redox couple with a formal potential (E_f) of 1.1 V versus Ag¦AgCl. The continuous cyclic voltammetric experiments showed that the Ru(II) microparticles are stable during the electrochemical conversions. The in situ spectroelectrochemical study showed that the absorbance at 463 nm decreased due to the oxidation of Ru(II) to Ru(III). Upon reduction, the growth of absorbance at 463 nm was observed due to the formation of Ru(II) complex and this process was reversible.     

Complexes of tris(o-phenanthroline)nickel(II) and copper(II) bromide with dithiocarbamates derived from α-amino acids

Complexes of 1,10-o-phenanthroline (o-phen)-Ni^II and Cu^II with dithiocarbamates derived from -amino acids (glycine, phenylalanine, alanine, methionine and tryptophan) were synthesized and characterized by chemical analysis, spectral and thermal studies and by biological screening; the complexes are non-electrolytes. The empirical formula are [Ni(o-phen)₂(aadtc)] and [Cu₂(o-phen)₂(phaladtc)(H₂O)₂Br₂] where, aadtc = glycinyl-, phenylalaninyl-, alaninyl-, methioninyl- and tryptophanyldithiocarbamate and phaladtc = phenylalaninyldithiocarbamate. The structure of these complexes is probably octahedral. Molecular association through hydrogen bonding between the —NH and the carboxylate groups is proposed for the Ni^II complexes. The Cu^II complex is dimeric with the phenylalaninyldithiocarbamate acting as a bridge.     

π-Extended and six-coordinate iron(II) complexes: structures, magnetic properties, and the electrochemical synthesis of a conducting iron(II) metallopolymer

Herein, we describe the preparation of three new bidentate π-extended derivatives of the ligand N-phenyl-2-pyridinalimine (ppi) containing a 3-thienyl (4) substituent at position 4 of the aniline ring or 2-thienyl (6) or phenyl (2) substituents at each of the 2,5 positions of the aniline rings. Three iron(2+) complexes (7-9) containing these ligands were prepared by combining two equivalents each of 2, 4, or 6 with Fe(NCS)(2), and the resulting neutral, six-coordinate complexes were fully characterized, including with single crystal X-ray diffraction experiments in the case of complexes 7 and 9. Variable temperature magnetic susceptibility and Mo?ssbauer experiments confirm the presence of spin-crossover in complexes 7 and 8, and the unusual solid state variable temperature magnetic properties of complex 9 likely result from crystal packing forces. Electropolymerization of the 2,5-dithienyl-substituted complex (9) produces a conducting and electrochromic metallopolymer film (poly-9).     

Synthesis and enantiomer separation of a modified tris(2,2′-bipyridine)ruthenium(II) complex

The chiral [5-(4-hydroxybutyl)-5′-methyl-2,2′-bipyridine]-bis(2,2′-bipyridine)-ruthenium(II)-bis(hexafluoroantimonate) complex 3 was prepared and characterized by different NMR techniques and successfully separated into enantiomers by electrokinetic chromatography using anionic carboxymethyl-β-cyclodextrin as chiral mobile phase additive (CMPA). The optimum separation conditions were obtained with 40 mM borate buffer at pH 9.5 and 7.5 mg/mL of the chiral selector at 20°C.     

O,O′-Alkylene dithiophosphate derivatives of iron(II) and iron(III) and their reactions with nitrogen- and phosphorus-donor bases

Summary Solids of the stoichiometric formulae [Fe{S₂P(OPr-n)₂}₃] and [Fe{S₂PO₂G}₃] (G = —CH₂CMe₂CH₂—, CMe_2–CMe₂— or —CH₂CH₂CHMe—) are precipitated from the reactions of FeCl₃ with ammonium dithiophosphates in water. Soluble complexes of the type [Fe{S₂PO₂G}₂], formed by the reactions of FeCl₂ with NH₄[{S₂PO₂G}] in MeOH, can be extracted with benzene. Adducts of the types [Fe{S₂PO₂G}₂L] and [Fe{S₂PO₂G}₂(PPh₃)₂] are formed by the reaction of [Fe{S₂PO₂G}₂] with L (L = 2,2-bipyridyl or 1,10-phenanthroline) and PPh₃, respectively. All the compounds have been characterized by i.r. and u.v.-vis. spectroscopy and magnetic studies.This paper is dedicated to the late Dr. G. Srivastava, Associate Professor, Department of Chemistry, Rajasthan University, Jaipur.     

Kinetics and mechanism of substitution of bis(tptz)iron(II) by 2,2′-bipyridine and 1,10-phenanthroline

The kinetics of substitution of Fe(tptz)²+₂ by 2,2-bipyridine and 1,10-phenanthroline have been investigated in acetate buffers in the 3.6–5.6pH range employing stopped-flow spectrophotometry. These reactions are very fast and complete within 5s. The rate of substitution is linearly dependent on [phen] and [bpy]², and increases with the increase in pH. Suitable mechanisms have been proposed involving the unprotonated form of the entering ligand, viz. bipyridine/phenanthroline as the reactive species. The pK_a values of bipyridine and phenanthroline, determined from the kinetic data, are in agreement with the literature values. It is concluded that the substitutions of iron(II)-diimine complexes also occur by an associative mechanism.     

Electrochemistry and UV/visible spectroscopy of phosphino-substituted bis(η-indenyl)iron(II) complexes

Six phosphino-functionalized diindenyl ferrocenes have been characterized by UV/vis spectroscopy and cyclic voltammetry in dichloromethane. The complexes contain the following ligands: 1-diphenylphosphino- (1), 1-diphenylphosphino-2-methyl- (2), 1-diphenylphosphino-3-methyl- (3), 1-diphenylphosphino-3-trimethylsilyl- (4), 1-diphenylphosphino-2,3-dimethyl- (5), and 1-diphenylphosphino-4,7-dimethyl-indenide (6). The cyclic voltammetry shows an approximately additive relationship between oxidation potential and the type of substituent and its ring position, but with increasing substitution leading to lower than otherwise expected oxidation potentials. The UV/vis spectra show two absorptions with the low energy band moving to lower energy with increasing substitution on the C₅ ring.     

Synthesis and magnetic properties of heterobinuclear copper(II)–iron(II) complexes with N,N′-bis(2-aminopropyl)oxamidocopper(II)

Six new -oxamido heterobinuclear complexes, namely [Cu(oxap)Fe(L)2]SO4, where oxap denotes the N,N-bis(2-aminopropyl)oxamido dianion and L represents 1,10-phenanthroline (phen); 5-nitro-1,10-phenanthroline (NO2-phen); 5-chloro-1,10-phenanthroline (Cl-phen); 5-methyl-1,10-phenanthroline (Me-phen); 2,2-bipyridine (bpy); and 4,4-dimethyl-2,2-bipyridine (Me2bpy), have been synthesized and characterized by elemental analyses, i.r. spectra, electronic spectra, magnetic moments (at room temperature) and molar conductivity measurements. The temperature dependent magnetic susceptibilities of [Cu(oxap)Fe(bpy)2]SO4 (1) and [Cu(oxap)Fe(phen)2]SO4 (2) have been studied in the 4.2–300K range, giving the exchange integrals J=–20.9cm–1 for (1) and J=–22.5cm–1 for (2). These results are commensurate with antiferromagnetic interactions between adjacent metal ions within each molecule.     

Synthesis and properties of iron(II) and iron(III) complexes with 3-(α,γ-dicarboxy-n-propylidene-hydrazino)-5,6-diphenyl-1,2,4-triazine (DCPT)

Summary Proton-ligand formation constants ofDCPT and metal-ligand formation constants of its complexes with Fe(II) and Fe(III) have been determined potentiometrically at 10, 20, 30, and 40°C in 75% (v/v) dioxane-water at 0.10M ionic strength (KNO₃). The thermodynamic parameters G, H, and S have also been evaluated. The possibility of formingM(HL),M(HL)₂, andM(HL)₃ species was substantiated from potentiometric and electronic absorption measurements. The values of the stability constants logK _M(HL), log , and log derived from the spectrophotometric method are in good agreement with those obtained from potentiometric data. The use ofDCPT as an analytical reagent for the spectrophotometric determination of iron is discussed. The solid complexes have been characterized by chemical analysis and magnetic susceptibility, IR, NMR, and electronic spectral data.

---

Synthese und Eigenschaften von Eisen(II)- und Eisen(III)-Komplexen mit 3-(,-Dicarboxy-n-propylidene-hydrazino)-5,6-diphenyl-1,2,4-triazin (DCPT)

Zusammenfassung Die Bildungskonstanten sowohl vonDCPT als auch seiner Komplexe mit Fe(II) und Fe(III) wurden bei 10, 20, 30 und 40°C in Dioxan-Wasser (75% (v/v)) bei einer lonenstärke von 0.1M KNO₃ potentiometrisch bestimmt. Zusätzlich wurden die thermodynamischen Parameter G, H und S ermittelt. Die Wahrscheinlichkeit des Auftretens von Komplexen der ArtM(HL),M(HL)₂ undM(HL)₃ wurde mittels potentiometrischer und absorptionsspektroskopischer Messungen erhärtet. Nach beiden Methoden ermittelte Stabilitätkonstanten stimmen gut überein. Die Verwendung vonDCPT als analytisches Reagens zur spektrophotometrischen Eisenbestimmung wird diskutiert. Die Komplexe konnten in Substanz hergestellt werden und wurden durch chemische Analyse und über ihre magnetischen und spektroskopischen Eigenschaften charakterisiert.

     

Synthesis and Characterization of Tris(2,2′-bipyridine) and tris(1,10-phenanthroline) Copper(II) Hexafluorophosphate. Crystal Structure of the Phenanthroline Complex

The tris-(bidentate)chelate complexes [Cu(NN)₃](PF₆)₂ where NN=2,2'-bipyridine or 1,10-phenanthroline have been isolated as secondary products in the reaction between the dimers [{Cu(NN)}₂(μ-OH)₂](PF₆)₂·2H₂O and di-2-pyridylketone. the X-ray crystal structure of [Cu(phen)₃](PF₆)₂ showed a distorted octahedral C ₂ geometry around teh metal atom, with two Cu-N distances being much longer than the other four. Magnetic susceptibility measurements (in the 4.4-290K range) correspond, in both cases, to a d⁹ configuration without significant magnetic interaction. A signal (g=2.102) was observed in the EPR spectrum of the bipy complex and the two axial components were resolved for the phen complex, with g_||=2.249, g_⊥=2.083 and A_||=137 x 10^-4cm^-1. In this case also a signal at g=2.128 is observed.     

Kinetics of cetyl trimethyl ammonium bromide catalyzed substitution of tris(sulfonated triazine)iron(II) complexes by 1,10-phenanthroline, 2,2′-bipyridine and 2,2′,6,2″-terpyridine

Transition Metal Chemistry - The kinetics of substitution of tris(3-(2-pyridyl)-5,6-bis(4-phenyl-sulfonic acid)-1,2,4-triazine)-iron(II), $$ {\text{Fe}}({\text{PDTS}})_{3}^{4 - } $$ , and...     

Synthesis and structure of mono- and dinuclear cyclopentadienyl–indenyl complexes of iron(II) and further reactions to mixed tri- and tetranuclear iron–cobalt complexes

The reaction of a mixture of sodium cyclopentadienide and the monolithium salt or dilithium salt of 2,2-bis(indenyl)propane with FeCl₂ leads to the mononuclear complex [(η⁵-C₅H₅)Fe(η⁵-ind-C(CH₃)₂-ind)] (ind = 1-indenyl) (1) and the dinuclear complex [{(η⁵-C₅H₅)Fe(η⁵-ind)}₂C(CH₃)₂] (2), respectively. [(η⁵-Me₅C₅)Fe(tmeda)Cl] reacts with dilithium 1,1′-biindenyl under formation of [{(η⁵-Me₅C₅)Fe}₂(μ-η⁵:η⁵-1,1′-biind)] (4). Due to the annelated arene rings of the η⁵-indenyl ligands, 2 and 4 may act as 4-electron donor ligands, as exemplified by the reaction with the triple-decker complex [{(η⁵-Me₅C₅)Co}₂(μ-η⁶:η⁶-toluene)], which afforded the tetranuclear dimer of triple-decker complexes [{(η⁵-C₅H₅)Fe(η⁵-Me₅C₅)Co(μ-η⁵:η⁴-1-ind)}₂C(CH₃)₂] (3) and the trinuclear complex [{(η⁵-Me₅C₅)Fe}₂(η⁵-Me₅C₅)Co(μ₃-η⁵:η⁴:η⁵-1,1′-biind)] · Et₂O (5 · Et₂O) by replacement of the central toluene deck, respectively. The [(η⁵-Me₅C₅)Co] fragments of 3 and 5 are bonded via the six-membered rings of the indenyl ligands in a η⁴-fashion. Caused by the coordination to the Co atoms the six-membered rings lose their planarity and adopt a butterfly structure. The coordination geometry of the Fe atoms is similar in all five complexes. Each Fe atom is coordinated by the C atoms of one of the five-membered rings of the indenyl ligands in a slightly distorted η⁵ manner (η³ + η²-coordination) and by a cyclopentadienyl ligand in a regular η⁵-fashion. The structures of 3 and 5 represent the first examples of slipped triple-decker complexes which comprise indenyl ligands in a μ-η⁵:η⁴ coordination mode.     

Highly sensitive spectrophotometric determination of olanzapine using cerium(IV) and iron(II) complexes of 1,10-phenanthroline and 2,2′-bipyridyl

Two highly sensitive spectrophotometric methods have been developed for the determination of olanzapine (OLP) in pharmaceuticals using cerium(IV) and iron(II) complexes of 1,10-phenanthroline and 2,2′-bipyridyl as reagents. The methods are based on the oxidation of OLP in acidic medium by a known excess of cerium(IV) followed by the determination of the unreacted oxidant by reacting with either ferroin and measuring the absorbance at 510 nm (method A) or iron(II)-2,2′-bipyridyl complex and measuring the absorbance at 525 nm (method B). The amount of cerium(IV) reacted corresponds to the amount of OLP. In both the methods, the absorbance is found to increase linearly with OLP concentration as shown by the correlation coefficient (r) of 0.9980 and 0.9958 for method A and method B, respectively. The calibration graphs are linear over the concentration range of 0.2–2.0 μg/mL in both the methods. The calculated molar absorptivity values are 1.00 × 10⁶ and 7.03 × 10⁵ L/mol cm, for method A and method B. The LOD and LOQ values for method A are calculated to be 0.04 and 0.13 μg/mL and the values are 0.07 and 0.22 μg/mL for method B, respectively. The methods were validated as per the current ICH guidelines. Both the methods gave similar results in terms of accuracy and precision. The RSD was less than 3% and the accuracy, obtained from recovery experiments, was 98.76–101.4%. The methods developed were applied to the determination of OLP in tablets and results agreed well with the label claim.     

Electronic and resonance Raman spectra of iron(II)—tetraazamacrocyclic complexes containing N-heterocyclic ligands

The adducts of the meso-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-1,4,8,11-tetraene iron(II) complex with N-heterocyclic ligands exhibit three characteristic absorption bands in the ranges 690-640, 505-470 and 435-340 nm. Using excitation wavelengths coinciding with the low energy band, a selective enhancement of the Raman vibrational modes of the macrocyclic ligand is observed, supporting the assignment of a metal-to-diimine charge-transfer transition. The high energy band is strongly dependent on the nature and pK_a, of the axial ligands. Excitation at this band leads to the enhancement of the N-heterocyclic vibrational modes in the Raman spectra, indicating a metal-to-(N-heterocycle) charge-transfer transition. The intermediate band exhibits weak resonance Raman activity. Its intensity depends on the proximity of the high energy band and is consistent with the occurrence of an intensity stealing mechanism.