Thermal and photochemical production of chromate(VI) ions from some complexes containing the “CrNO”2+ group

Results are reported for the oxidation of complexes of the type [Cr(CN)_5?x(H₂O)_xNO]^x?3 by molecular oxygen in alkaline medium. In the case of the [Cr(CN)₅NO]^3? complex the reaction proceeded photochemically, whereas in othe cases the thermal oxidation was also observed. The influence of pH, CN^? concentration and energy of radiation was investigated.     

The kinetics and mechanism of the substitution reactions of the aquapentacyanoruthenate(II) ion with naphthalene‐substituted ligands in aqueous medium

The kinetics and mechanism of substitution reaction of [Ru(CN)₅H₂O]^3? anion with two naphthalene‐substituted ligands viz. Lⁿ = nitroso‐R‐salt (NRS) and α‐nitroso‐β‐naphthol (αNβN) have been studied spectrophotometrically by monitoring an increase in absorbance at λ_max = 525 nm corresponding to metal to ligand charge transfer (MLCT) transitions due to formation of substituted [Ru(CN)₅L]^n?3 as a function of pH, ionic strength, temperature, a wide range of ligands concentration, and [Ru(CN)₅H₂O^3?] under pseudo‐first‐order conditions. The experimental observation suggests that [Ru(CN)₅H₂O]^3? ion interacts with both ligands, which finally get converted into corresponding, [Ru(CN)₅L]^n?3 complexes as a final reaction product. The reaction is found to obey first‐order dependence each in [Ru(CN)₅H₂O^3?] and [Lⁿ]. The substituted products, viz. [Ru(CN)₅L]^n?3, in each case have strong MLCT transitions in visible region. The substitutional lability of [Ru(CN)₅H₂O]^3? has been discussed in terms of electronic effect on the M? OH₂ bond interactions. The kinetic observation suggests that the complexation reaction of [Ru(CN)₅H₂O]^3? with both the ligands, i.e., NRS and αNβN, follows an ion pair dissociative mechanism. The thermal activation parameters ΔH^≠ and ΔS^≠ have been calculated using Eyring's equation and provided in support for the proposed mechanistic scheme. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 43: 21–30, 2011     

Reductive nitrosylation of tetraoxometallates. part V1. single pot and A virtually single step synthesis of chromium(l) cyanonitrosyl derivatives directly from chromate(VI) in aqueous-aerobic media.

Cyanonitrosyl complexes and their derivatives of the types [Cr(NO)(CN)₄]^2?, [Cr(NO)(CN)₃H₂O]^? and [Cr(NO)(CN)₂ LL] [LL = 2,2′ bipyridine (bipy) or 1, 10-Phenanthroline (phen)] are synthesised directly from CrO₄^2? using NH₂OH.HCl, OH^? and CN^? and other appropriate ligands, virtually in a single step process in an aqueous aerobic medium. The compounds are characterised by IR, molar conductance, magnetic susceptibility, e.s.r, electronic spectra and thermoanalytical data.     

Charakterisierung von Distorsionsisomeren der Anionen Pentacyano-oxo-molybdat(IV) sowie Tetracyano-oxo-aqua-molybdat(IV) im festen Zustand. Kristallstrukturen von [(C6H5)4P]3[MoO(CN)5] · 7 H2O(grün), [(C6H5)4As]2 [MoO(OH2)(CN)4] · 4 H2O (blau) und [(C6H5)4P]2[MoO(OH2)(CN)4] · 4 H2O (grün)

Characterization of Distortional Isomers of the Anions Pentacyano-oxo-molybdate(IV) and of Tetracyano-aqua-oxo-molybdate(IV) in the Solid State. Crystal Structures of [(C₆H₅)₄P]₃[MoO(CN)₅] · 7 H₂O (green), [(C₆H₅)₄As]₂[MoO(OH₂)(CN)₄] · 4 H₂O (blue), and [(C₆H₅)₄P]₂[MoO(OH₂) (CN)₄] · 4 H₂O (green) Preparation of a series of salts containing the new pentacyano-oxo-molybdate(IV) anion is described: Cs₂H[MoO(CN)₅] (blue), [(CH₃)₄N]₂H[MoO(CN)₅] · 2 H₂O (blue) and [Cr(en)₃] [MoO(CN)₅] · 4 H₂O (green). The green [(C₆H₅)₄P]₃[MoO(CN)₅] · 7 H₂O crystallizes triclinic in the space group P1 . The molybdenum(IV) center is in an pseudo-octahedral environment of a terminal oxo-group (d(Mo?O); 1.705(4) Å), a CN^? group in the trans-position (d(Mo? C): 2.373(6) Å), and four equatorial CN^? groups (averaged d(Mo? C): 2.178 (Å). The blue and green salts exhibit v(Mo?O) stretching frequencies at 948 cm^?1 and 920 cm^?1, respectively. Blue and green salts containing the [MoO(OH₂)(CN)₄]^2? anion and [(C₆H₅)₄P]⁺ or [(C₆H₅)₄As]⁺ cations have been prepared and characterized by single crystal crystallography. [(C₆H₅)₄P]₂[MoO(OH₂)(CN)₄] · 4 H₂O (green) and [(C₆H₅)₄As]₂[MoO(OH₂)(CN)₄] · 4 H₂O (blue) crystallize monoclinic in the space group C—P2₁/n. They are considered to be distortional isomers of the complex anion: the green species has a Mo?O bond distance of 1.72(2) Å whereas for the blue species d(Mo?O) = 1.60(2) Å is found; the corresponding v(Mo?O) frequencies are at 920 cm^?1 and 980 cm^?1.     

Cyanide-bridged one-dimensional bimetallic complexes based on a tridentate copper(II) building block: synthesis,crystal structures and magnetic properties

The reactions of [M^III(CN)₆]^3? (M = Cr or Co) with Cu^II complexes of a tridentate schiff base [Cu(aemp)Cl] or [Cu(aemp)Ac]₂ (Haemp = 2-[(2-amino-ethylimino)-methyl]-phenol) give rise to 1D cyanide-bridged bimetallic coordination polymers [Cu₄(aemp)₄(H₂O)₂][Cr(CN)₆]Cl (1) and [Cu₃(aemp)₃(H₂O)][Co(CN)₆]·2H₂O·MeOH (2). In complex 1, the six cyanide ligands of the [Cr(CN)₆]^3? moiety are involved in bridging, while in complex 2 only five cyanide ligands act as bridges to give a neutral chain. Magnetic studies reveal that complex 1 exhibits intermetallic ferromagnetic coupling, with J = 8.2 cm^?1.     

Crystal structure of a cyanide-bridged heptanuclear manganese(III)–chromium(III) complex with a ground state S = 21/2

K₃[Cr(CN)₆] reacts with the mononuclear Mn^III complex Mn(salen)ClO₄ · 2H₂O [salen: N,N-ethylenebis(salicylideneiminato)dianion] to give a bimetallic heptanuclear complex cation salt [Cr{(CN)Mn(salen · H₂O)}₆][Cr(CN)₆]6H₂O. In the complex anion, [Cr{(CN)Mn(salen · H₂O)}₆]³⁺, six Mn^III ions coordinate to a Cr^III center via cyano bridges, forming a spherical species with 3 symmetry. A study of magnetic properties shows the presence of antiferromagnetic interaction through the cyanide bridge between Cr^III (S = 3/2) and Mn^III (S = 4/2) and results in a ground state S = 21/2.     

Synthesis,Crystal Structures and Magnetic Properties of Ion-Pair Complexes with Hydrogen Bonding Network: Ln(DMA)n(H2O)m Cr(CN)6· xH2O(Ln = Sm,Gd: n = 4, m = 3, x = 2; Ln = Er: N = 3, m = 4, x = 0)

Three ion-pair Ln-Cr complexes [Sm(DMA)₄(H₂O)₃][Cr(CN)₆] · 2H₂O, [Gd(DMA)₃(H₂O)₄][Cr(CN)₆] · 2H₂O and [Er(DMA)₃(H₂O)₄][Cr(CN)₆] (DMA = dimethylacetamide) have been synthesized. X-ray structure analyses of the title complexes revealed that there is a hydrogen-bonding network through CN groups and H₂O molecules. Variable temperature magnetic susceptibilities indicate weak antiferromagnetic interactions between cation and anion pairs moderated through the hydrogen bonding network.     

Kinetics and mechanism of oxidation of the binary and ternary complexes of chromium(III) involving inosine and glycine by N -bromosuccinimide

The kinetics of oxidation of the chromium(III) complexes, [Cr(Ino)(H₂O)₅]³⁺ and [Cr(Ino)(Gly)(H₂O)₃]²⁺ (Ino?=?Inosine and Gly?=?Glycine) involving a ligands of biological significance by N-bromosuccinimide (NBS) in aqueous solution to chromium(VI) have been studied spectrophotometrically over the 25–45°C range. The reaction is first order with respect to both [NBS] and [Cr], and increases with pH over the 6.64–7.73 range in both cases. The experimental rate law is consistent with a mechanism in which the hydroxy complexes [Cr(Ino)(H₂O)₄(OH)]²⁺ and [Cr(Ino)(Gly)(H₂O)₂(OH)]⁺ are significantly more reactive than their conjugate acids. The value of the intramolecular electron transfer rate constant, k ₁, for the oxidation of the [Cr(Ino)(H₂O)₅]³⁺ (6.90?×?10^?4?s^?1) is lower than the value of k ₂ (9.66?×?10^?2?s^?1) for the oxidation of [Cr(Ino)(Gly)(H₂O)₂]²⁺ at 35°C and I?=?0.2?mol?dm^?3. The activation parameters have been calculated. Electron transfer apparently takes place via an inner-sphere mechanism.     

Kalium-μ-dithio-bis(pentacyanokobaltat(III)) und Kalium-μ-diseleno-bis(pentacyanokobaltat(III))

Potassium-μ-dithio-bis(pentacyanocobaltate(III)) and Potassium-μ-diseleno-bis(pentacyanocobaltate(III)) The oxidation of [Co(CN)₅]^3? by sulfur or selenium leads to the complexes [Co₂S₂(CN)₁₀]^6? and [Co₂Se₂(CN)₁₀]^6?, respectively, which have been isolated as potassium salts K₆[Co₂S₂(CN)₁₀] · 4 H₂O and K₆[Co₂Se₂(CN)₁₀] · 5 H₂O. The μ-dithio complex has also been formed from [Co(CN)₅]^3? with polysulfide, from [CoOH(CN)₅]^3? with H₂S + O₂ and from [Co₂O₂(CN)₁₀]^6? with H₂S. As shown by their vibrational spectra the new complexes contain bridges Co? S? S? Co and Co? Se? Se? Co, respectively.     

Solving the 170‐Year‐Old Mystery About Red‐Violet and Blue Transient Intermediates in the Gmelin Reaction

The Gmelin reaction between nitroprusside and sulfides in aqueous solution is known to produce two transient intermediates with distinct colors: an initial red‐violet intermediate that subsequently converts into a blue intermediate. In this work, we use a combination of multinuclear (¹⁷O, ¹⁵N, ¹³C) NMR, UV/Vis, IR spectroscopic techniques and quantum chemical computation to show unequivocally that the red‐violet intermediate is [Fe(CN)₅N(O)S]^4? and the blue intermediate is [Fe(CN)₅N(O)SS)]^4?. While the formation of [Fe(CN)₅N(O)S]^4? has long been postulated in the literature, this study provides the most direct proof of its structure. In contrast, [Fe(CN)₅N(O)SS)]^4? represents the first example of any metal coordination complex containing a perthionitro ligand. The new reaction pathways found in this study not only provide clues for the mode of action of nitroprusside for its pharmacological activity, but also have broader implications to the biological role of H₂S, potential reactions between H₂S and nitric oxide donor compounds, and the possible biological function of polysulfides.     

Substituting group induced structural transformation from 1D zigzag chain to 2D grid network in cyano-bridged dimetallic complexes derived from Mn(Schiff-base) and [Cr(CN)5NO]: Synthesis, crystal structure and magnetic properties

Two cyano-bridged dimetallic complexes derived from Mn^III(Schiff-base) and [Cr^I(CN)₅NO]³⁻, [Mn(3-CH₃)salen]₃[Cr(CN)₅NO]·2.5H₂O (1) and [Mn(5-CH₃)salen]₆[Cr(CN)₅NO]₂·2CH₃OH·16H₂O (2) [salen = N,N′-ethylenebis (salicylideneiminato)dianion] were synthesized and characterized. The reaction conditions of the two complexes are identical. The substituting group (CH₃-) in the salen-type ligands gives different assembly styles for the two complexes, 1D zigzag chain for 1 while 2D grid network for 2. The magnetic investigation indicates the dominant antiferromagnetic interactions between the Mn(III) and Cr(I) mediated by the CN bridge. Due to the weak interchain antiferromagnetic interactions, no magnetic ordering phase was observed in complex 1. Interestingly, complex 2 showed the long range ferrimagnetic magnetic ordering with T_c = 9 K, in contrast to 1. Furthermore, the hysteresis loop confirms the nature of complex 2 as soft ferrimagnet.     

The HNO donor ability of hydroxamic acids upon oxidation with cyanoferrates(III)

The hydroxamic acids (RC(O)NHOH, HA) exhibit diverse biological activity, including hypotensive properties associated with formation of nitroxyl (HNO) or nitric oxide (NO). Oxidation of two HAs, benzohydroxamic and acetohydroxamic acids (BHA, AHA) by [Fe(CN)₅NH₃]^2? or [Fe(CN)₆]^3? was analyzed by spectroscopic, mass spectrometric techniques, and flow EPR measurements. Mixing BHA with both Fe(III) reactants at pH 11 allowed detecting the hydroxamate radical, (C₆H₅)C(O)NO˙^?, as a one-electron oxidation product, as well as N₂O as a final product. Successive UV–vis spectra of mixtures containing [Fe(CN)₅NH₃]^2? (though not [Fe(CN)₆]^3?) at pH 11 and 7 revealed an intermediate acylnitroso-complex, [Fe(CN)₅NOC(O)(C₆H₅)]^3? (λ_max, 465 nm, very stable at pH 7), formed through ligand interchange in the initially formed reduction product, [Fe(CN)₅NH₃]^3?, and characterized by FTIR spectra through the stretching vibrations ν_(CN), ν_(CO), and ν_(NO). Free acylnitroso derivatives, formed by alternative reaction paths of the hydroxamate radicals, hydrolyze forming RC(O)OH and HNO, postulated as precursor of N₂O. Minor quantities of NO are formed only with an excess of oxidant. The intermediacy of HNO was confirmed through its identification as [Fe(CN)₅(HNO)]^3? (λ_max, 445 nm) as a result of hydrolysis of [Fe(CN)₅(NOC(O)(C₆H₅)]^3? at pH 11. The results demonstrate that hydroxamic acids behave predominantly as HNO donors.     

Metallkomplexe mit anionischen Liganden von Elementen der 4. Hauptgruppe. VIII. Pentacarbonyl-trihalogenstannido-metallat(O)-Komplexe von chrom,molybdän und wolfram mit fluor- und jodhaltigen stannidliganden

Metal Complexes with Anionic Ligands of Elements of the Main Group IV. VIII Pentacarbonyltrihalogenostannidometalate(O) Complexes of Chromium, Molybdenum, and Tungsten with Fluorine and Iodine Containing Trihalogenostannido Ligands In methylenechloride [As(C₆H₅)₄][SnF₃] readily reacts with the metalhexacarbonyls forming the arsoniumsalts of the pentacarbonyltrifluorostannidometalate(O) complexes, [M(CO)₅SnF₃]^? (M ? Cr, Mo, W). Exclusively by the reaction of the intermediately formed complex Cr(CO)₅THF only one pure triiodostannidometalate(O) Complex, [N(C₂H₅)₄][Cr(CO)₅SnJ₃], could be isolated. The trihalogenostannidometalate(O) complexes [M(CO)₅SnClX₂]^? (X ? F: M ? Cr, Mo, W; X ? J: M ? Cr) could be prepared by SnX₂-insertion reactions of the [M(CO)₅Cl]^? complexes. The bonding properties of the halogenostannide ions are discussed on the bases of the IR spectra of their metalate(O) complexes.     

ELECTRONIC STRUCTURE OF CYANO-BRIDGED DINUCLEAR IRON COMPLEXES

Abstract

A series of complexes of formula [(NC)₅Fe^II—NC—Fe^II(CN)₄L]^n?, with L = H₂O, pyridine, isonicotinamide and 4-cyanopyridine were prepared in aqueous solution by substitution of the corresponding [Fe^II(CN)₅L]^n? ions into [Fe^II(CN)₅H₂O]^3?. The mixed valent (II, III) and fully oxidized (III, III) complexes were also obtained. The (II, II) complexes were moderately stable toward dissociation into the mononuclear species, but the mixed-valent ions were properly characterized by UV-vis-NIR spectroscopy and electrochemistry. Distinctive intervalence (IV) bands were assigned in the NIR region, with the energy being dependent on the binding properties of L; the IV band energy also correlated with the redox potential at the [NC—Fe(CN)₄L] fragment. By application of the Hush model, a valence-trapped situation was found for the [(NC)₅Fe^III—NC—Fe^II(CN)₄L]^n? ions. The class II behavior shows, however, a value of H _ab, the electronic coupling factor, of ca. 1600cm^?1, indicating a moderate-to-strong communication between the metal centers.     

Zur kenntnis der cyclopentadienyl-nitrosyl-carbonyl-isonitril-komplexe der VI. Und der cyclopentadienyl-dicarbonyl-isonitril-komplexe der VII. Nebengruppe

The nitrosylcarbonylisonitrile complexes η⁵-C₅H₅M(NO)(CO)CNR (R = Me for Cr, Mo, W; R = Et, SiMe₃, GeMe₃, SnMe₃ for Mo) are formed by treatment of the nitrosylcarbonylcyanometalates Na[η⁵-C₅H₅M(NO)(CO)CN] with [R₃O]BF₄ (R = Me, Et), Me₃SiCl, Me₃GeCl or Me₃SnCl. The isoelectronic dicarbonylisonitrile compounds η⁵-C₅H₅Mn(CO)₂CNR (R = SiMe₃, GeMe₃, SnMe₃, PPh₂, AsMe₂) and η⁵-C₅H₅Re(CO)₂CNAsMe₂ are obtained by analogous reactions of Na[η⁵-C₅H₅M(CO)₂CN] (M = Mn, Re) with Me₃ECl (E = Si, Ge, Sn), Ph₂PCl and Me₂AsBr.With phosgene the anionic complexes Na[η⁵-C₅H₅M(CO)₂CN] (M = Mn, Re) can be transformed into the new carbonyldiisocyanide-bridged dinuclear complexes η⁵-C₅H₅M(CO)₂CN-C(O)-NC(OC)₂M-η⁵-C₅H₅. Finally, the reactions of η⁵-C₅H₅M(NO)(CO)CNMe (M = Cr, Mo, W) with NOPF₆, leading to the cationic dinitrosylisonitrile complexes [η⁵-C₅H₅M(NO)₂CNMe]⁺, are described.     

Kinetics of anation of chromium(III) by L-phenylalanine

Summary The kinetics of anation of chromium(III) species, [Cr(H₂O)₆]⁴⁺ and [Cr(H₂O)₅OH]²⁺, by L-phenylalanine in aqueous acid has been studied spectrophotometrically. Effects of varying [substrate], [ligand], [H⁺], , % ethanol and temperature were investigated. The kinetic data suggest a mechanism where outersphere-associations [between chromium(III) species and phenylalanine in the zwitterionic form] precede anation. Comparison of the results with published data suggest an I_a path for the [Cr(H₂O)₆]³⁺ reaction and I_d path for the [Cr(H₂O)₅OH]²⁺ reaction.     

3d-Metal Nitroprusside–Thiosemicarbazide Complexes: Synthesis and Properties

The following complexes were synthesized from 3d-metal nitroprussides and thiosemicarbazide: [CrL₃][Fe(CN)₅H₂O] · 6H₂O, [FeL₃]₂[Fe(CN)₅NO]₃ · 14H₂O, [CoL₃]₂[Fe(CN)₅NO]₃ · 4H₂O, [NiL₂][Fe(CN)₅NO], [CuL₂][Fe(CN)₅NO] · 5H₂O, and [[ZnL₂][Fe(CN)₅NO], where L is thiosemicarbazide. Their structures and properties were studied by IR and diffuse reflection spectroscopies and DTA.     

Diamond‐ and Graphite‐Like Octacyanometalate‐Based Polymers Induced by Metal Ions

By using cyclohexane‐1,2‐diamine (chxn), Ni(ClO₄)₂ ? 6H₂O and Na₃[Mo(CN)₈] ? 4H₂O, a 3D diamond‐like polymer {[Ni^II(chxn)₂]₂[Mo^IV(CN)₈] ? 8H₂O}_n ( 1 ) was synthesised, whereas the reaction of chxn and Cu(ClO₄)₂ ? 6H₂O with Na₃[M^V(CN)₈] ? 4H₂O (M=Mo, W) afforded two isomorphous graphite‐like complexes {[Cu^II(chxn)₂]₃[Mo^V(CN)₈]₂ ? 2H₂O}_n ( 2 ) and {[Cu^II(chxn)₂]₃[W^V(CN)₈]₂ ? 2H₂O}_n ( 3 ). When the same synthetic procedure was employed, but replacing Na₃[Mo(CN)₈] ? 4H₂O by (Bu₃NH)₃[Mo(CN)₈] ? 4H₂O (Bu₃N=tributylamine), {[Cu^II(chxn)₂Mo^IV(CN)₈][Cu^II(chxn)₂] ? 2H₂O}_n ( 4 ) was obtained. Single‐crystal X‐ray diffraction analyses showed that the framework of 4 is similar to 2 and 3 , except that a discrete [Cu(chxn)₂]²⁺ moiety in 4 possesses large channels of parallel adjacent layers. The experimental results showed that in this system, the diamond‐ or graphite‐like framework was strongly influenced by the inducement of metal ions. The magnetic properties illustrate that the diamagnetic [Mo^IV(CN)₈] bridges mediate very weak antiferromagnetic coupling between the Ni^II ions in 1 , but lead to the paramagnetic behaviour in 4 because [Mo^IV(CN)₈] weakly coordinates to the Cu^II ions. The magnetic investigations of 2 and 3 indicate the presence of ferromagnetic coupling between the Cu^II and W^V/Mo^V ions, and the more diffuse 5d orbitals lead to a stronger magnetic coupling interaction between the W^V and Cu^II ions than between the Mo^V and Cu^II ions.     

Photoredox chemistry of nitrosylpentacyanoferrate(II) in methanolic medium

The solvent complexes [Fe(CN)₅(CH₃OH]^2? and [Fe(CN)₅CH₃O]^3? were found to be the main products of the photochemical reactio     

Kinetics and mechanism of the ligand substitution reaction between aquapentacyanoruthenate(II) and 4-cyanopyridine in the presence of anionic surfactant micelles

The kinetics of ligand substitution between aquapentacyanoruthenate(II) ion, [Ru(CN)₅H₂O]³⁻ and 4-cyanopyridine (4-CNpy) has been investigated spectrophotometrically in the presence of anionic surfactant micelle, namely sodium dodecylsulphate (SDS) at 400 nm (λ_max of the intense yellow product [Ru(CN)₅4-CNpy]³⁻) under pseudo-first-order conditions using at least 10% excess of 4-CNpy over [Ru(CN)₅H₂O]³⁻. The reaction was studied as a function of [Ru(CN)₅H₂O³⁻], [4-CNpy], [SDS], pH, ionic strength and temperature, by varying each of these variables one at a time. The reaction exhibited overall second-order kinetics, being first order each in [4-CNpy] and [Ru(CN)₅H₂O³⁻] over a wide concentration range. Variation of ionic strength of the medium had a significant negative effect on the rate. The SDS micelle, being negatively charged, does not reveal any regular effect except at or near its critical micelle concentration (c.m.c). The rate of reaction was measured at different temperatures, and the activation parameters were computed using Arrhenius and Eyring plots. A plausible mechanism consistent with the experimental results has been proposed.