Stable Salts of Heteroleptic Iron Carbonyl/Nitrosyl Cations

The oxidation of Fe(CO)₅ with the [NO]⁺ salt of the weakly coordinating perfluoroalkoxyaluminate anion [F‐{Al(OR^F)₃}₂]^? (R^F=C(CF₃)₃) leads to stable salts of the 18 valence electron (VE) species [Fe(CO)₄(NO)]⁺ and [Fe(CO)(NO)₃]⁺ with the Enemark–Feltham numbers of {FeNO}⁸ and {FeNO}¹⁰. This finally concludes the triad of heteroleptic iron carbonyl/nitrosyl complexes, since the first discovery of the anionic ([Fe(CO)₃(NO)]^?) and neutral ([Fe(CO)₂(NO)₂]) species over 80 years ago. Both complexes were fully characterized (IR, Raman, NMR, UV/Vis, scXRD, pXRD) and are stable at room temperature under inert conditions over months and may serve as useful starting materials for further investigations.     

Optical properties,structural, and DFT studies of Pd(II) complexes with 1-phenyl-1H-tetrazol-5-thiol,X-ray crystal structure of [Pd(κ1-S-ptt)2(κ2-dppe)] complex

Seven tetrazole-thione complexes, [Pd₂(κ²-ptt)₄]( 1 ), trans-[Pd(k¹-S-ptt)₂(PPh₃)₂] ( 2 ), trans-[Pd(k¹-S-ptt)₂(SPPh₃)₂] ( 3 ), trans-[Pd(k¹-S-ptt)₂(OPPh₃)₂] ( 4 ), [Pd(k¹-N-ptt)₂(k²-dppe)] ( 5a ), [Pd(k¹-S-ptt)₂(k²-dppe)] ( 5b ), [Pd(k¹-S-ptt)₂(k²-dppeS₂)] ( 6 ), and [Pd(k¹-S-ptt)₂(k²-dppeO₂)] ( 7 ), were prepared from 1-phenyl-1H-tetrazole-5-thiol (Hptt), with substituted phosphines. These complexes were investigated by CHNS analysis; infrared (IR), nuclear magnetic resonance (NMR) (¹H and ³¹P), and ultraviolet–visible (UV–Vis) spectroscopy; and single-crystal X-ray data for 5b . In Complex 1 , the ptt⁻ ligand adopted μ²- k-N, k-S bridging mode to afford a dimeric complex, whereas in Complexes 2–4 , 6 , and 7 , the ptt⁻ was covalently coordinated via sulfur atom of the thiol group as a solo product. In contrast, in Complex 5 , the ptt⁻ ligand was bonded in a monodentate fashion through a deprotonated tetrazole ring nitrogen atom in isomer 5a or via a thiolato sulfur atom in isomer 5b . These linkage isomers were clearly shown in the ³¹P-{¹H} NMR. To explain the adoption of the ligand binding modes in Complexes 5a and 5b , geometry optimization calculations were carried out on two isomers. Very small differences of all molecular parameters were found between 5a and 5b isomers. This confirms the reason for obtaining two isomers. Also, theoretical studies are made for all compounds, and excellent agreement is obtained with experimental data. The direct band gap (Eg) values are equal to 2.88, 2.85, and 2.45 eV for Complexes 1 , 2 , and 4 , respectively, revealing a semiconductor nature. The inhibition activity of Complexes 1–3 , 5 , and 8 were evaluated versus the growth of four types of bacteria in vitro. The complexes showed a good activity compared with free ligand and a standard antibiotic.     

Raman studies of the hydrated melt of FeCl36H2O

The hydrated melt of FeCl₃6H₂O has been investigated by laser Raman spectroscopy. Application of the background correction and band fitting computational methods has revealed that the hydrated melt predominantly contains an octahedral species, Fe(H₂O)₄Cl⁺₂, and a tetrahedral species, FeCl⁻₄. These are present in almost equal concentrations because the hydrated melt produces about twice the amount of contained FeCl⁻₄ species in the presence of excess CL⁻ ion. The relatively high electrical conductivity of the hydrated melt is consistent with the ionic species [Fe(H₂O)₄Cl₂]⁺ and [FeCl₄]⁻, rather than a bitetrahedral species, Fe₂Cl₆.     

Spectroscopic and Computational Study of a Nonheme Iron Nitrosyl Center in a Biosynthetic Model of Nitric Oxide Reductase

A major barrier to understanding the mechanism of nitric oxide reductases (NORs) is the lack of a selective probe of NO binding to the nonheme Fe_B center. By replacing the heme in a biosynthetic model of NORs, which structurally and functionally mimics NORs, with isostructural ZnPP, the electronic structure and functional properties of the Fe_B nitrosyl complex was probed. This approach allowed observation of the first S=3/2 nonheme {FeNO}⁷ complex in a protein‐based model system of NOR. Detailed spectroscopic and computational studies show that the electronic state of the {FeNO}⁷ complex is best described as a high spin ferrous iron (S=2) antiferromagnetically coupled to an NO radical (S= 1/2) [Fe²⁺‐NO^.]. The radical nature of the Fe_B‐bound NO would facilitate N? N bond formation by radical coupling with the heme‐bound NO. This finding, therefore, supports the proposed trans mechanism of NO reduction by NORs.     

[Na(15-Krone-5)][ReFCl3(NO)(CH3CN)] Synthese,IR-Spektrum und Kristallstruktur

[Na(15-crown-5)][ReFCl₃(NO)(CH₃CN)] Synthesis, IR Spectrum, and Crystal Structure The title compound has been prepared by the reaction of [ReCl₃(NO)₂(CH₃CN)] with the equivalent amount of sodium fluoride in the presence of 15-crown-5 in boiling acetonitrile, forming blue crystals. They were characterized by IR spectroscopy and by an X-ray structure determination. Space group P2₁/n, Z = 4,2117 observed independent reflections, R = 0.037, wR = 0.029. Lattice dimensions at 20°C: a = 834.0(2), b = 1600.0(3), c = 1670.0(3) pm; β = 104.19(3)°. The compound forms an ion pair via one Na F contact of 234.4 pm and one Na Cl contact of 293.4 pm; the nitrosyl ligand ist in trans-position to the F atom of the anion [ReFCl₃(NO)(CH₃CN)]⁻.     

One Electron Makes Differences: From Heme {FeNO}7 to {FeNO}8

The first X‐ray single‐crystal structure of a {FeNO}⁸ porphyrin complex [Co(Cp)₂][Fe(TFPPBr₈)(NO)], and the structure of the {FeNO}⁷ precursor [Fe(TFPPBr₈)(NO)] are determined at 100 K. The two complexes are also characterized by FTIR and UV/Vis spectroscopy. [Fe(TFPPBr₈)(NO)]^? shows distinct structural features in contrast to a nitrosyl iron(II) porphyrinate on the Fe? N? O^? moiety, which include a much more bent Fe? N? O^? angle (122.4(3)°), considerably longer Fe? NO^? (1.814(4)) and N? O^? (1.194(5) Å) bond distances. These and the about 180 cm^?1 downshift ν_N‐O stretch (1540 cm^?1) can be understood by the covalently bonding nature between the iron(II) and the NO^? ligand which possesses a two‐electron‐occupied π* orbital as a result of the reduction. The overall structural features of [Fe(TFPPBr₈)(NO)]^? and [Fe(TFPPBr₈)(NO)] suggest a low‐spin state of the iron(II) atom at 100 K.     

Reactivity of Cyanide and Thiocyanate Towards the Nitrosyl Carbonyl [Co(CO)3(NO)]

The reaction of equimolar amounts of [Co(CO)₃(NO)] and [PPN]CN, PPN⁺ = (PPh₃)₂N⁺, in THF at room temperature resulted in ligand substitution of a carbonyl towards the cyanido ligand presumably affording the complex salt PPN[Co(CO)₂(NO)(CN)] as a reactive intermediate species which could not be isolated. Applying the synthetic protocol using the nitrosyl carbonyl in excess, the title reaction afforded unexpectedly the novel complex salt PPN[Co₂(μ-CN)(CO)₄(NO)₂] ( 1 ) in high yield. Because of many disorder phenomena in crystals of 1 the corresponding NBu₄⁺ salt of 1 has been prepared and the molecular structure of the dinuclear metal core in NnBu₄[Co₂(μ-CN)(CO)₄(NO)₂] ( 2 ) was determined by X-ray crystal diffraction in a more satisfactory manner. In contrast to the former result, the reaction of [PPN]SCN with [Co(CO)₃(NO)] yielded the mononuclear complex salt PPN[Co(CO)₂(NO)(SCN-κN)] ( 3 ) in good yield whose molecular structure in the solid was even determined and its composition additionally confirmed by spectroscopic means.     

Six-coordinated oxovanadium(V) complexes of reduced Schiff bases derived from amino acids: synthesis,reactivity and redox studies

New oxovanadium(V) complexes, [VOL(hq)] (1)–(4) have been prepared by the reaction of [VO(acac)₂] with ligands LH₂ in the presence of 8-hydroxyquinoline (Hhq). LH₂ is the dibasic tridentate ONO Mannich base [(S)-H₂glysal, (S)-H₂alasal, (S)-H₂leusal and (S)-H₂ileusal; S represents the S-enantiomer] obtained by the reduction of the Schiff bases of salicylaldehyde (sal) and the amino acids: glycine (gly), DL-alanine (ala), leucine (leu) and isoleucine (ileu), respectively. Spectral studies suggest an octahedral structure for these complexes. The complexes exhibit a single ⁵¹V-n.m.r. signal at –464.6 to –468.0 p.p.m. due to the existence of a single isomeric species in solution. In the presence of L-ascorbic acid under aerobic conditions [VO(S-glysal)(hq)] (1) and [VO(S-isoleusal)(hq)] (4) are converted into the corresponding dioxo species possible via intermediate reduction. A time- dependent ⁵¹V-n.m.r. study has also been carried out in order to investigate the possible isomerisation and/or further reaction in solution.     

Two Novel Oxamidato-bridged Tetranuclear Complexes M[Cu(PMoxd)]3(ClO4)2 (M=Mn, Ni, Cu(PMoxd)=N,N′-bis(pyridyl-methyl)-oxamidatocopper(II)): Syntheses, Spectra, Magnetic and Electrochemical Properties

Two novel oxamidato-bridged Mn[Cu(PMoxd)]₃(ClO₄)₂ (1) Ni[Cu(PMoxd)]₃(ClO₄)₂ (2) tetranuclear complexes were prepared and characterized by i.r., e.p.r., electronic spectra, cyclic voltammograms, and magnetic properties. The magnetic analysis was carried out by means of the theoretical expression of the magnetic susceptibility deduced from the spin Hamiltonian H=−2JS_M(S_Cu1+ S_Cu2 + S_Cu3) (M=Mn, Ni), leading to J=−20.4 cm⁻¹; −121.1 cm⁻¹ for complexes (1) and (2) respectively. Magnetic measurements indicate that the overall magnetic behavior of the tetranuclear species are antiferromagnetic.     

Kinetics and mechanism of reaction of trans-(diaqua)(N,N′-ethylene-bis-salicylidenimine) chromium(iii) with sulfur(iv): The labilizing effect of coordinated sulfite

The reaction of trans-[Cr(Salen)(OH₂)₂]⁺ with aqueous sulfite yields trans-[Cr(Salen)(OH₂)(OSO₂(SINGLEBOND)O)]⁻ (O-bonded isomer). The rate and activation parameter data for the formation of the sulfito complex are consistent with a mechanism involving rate-limiting addition of SO₂ to the Cr^III(SINGLEBOND)OH bond. The complex ions, trans-[(OH₂)Cr(Salen)(OSO₂(SINGLEBOND)O)]⁻, and trans-[(OH)Cr(Salen)(OSO₂(SINGLEBOND)O)]²⁻, undergo reversible anation by NCS⁻, N₃⁻, imidazole, and pyridine resulting in the formation of trans-[XCr(Salen)(OSO₂(SINGLEBOND)O)]^(N+1)−(n=1 for X=N₃⁻,NCS⁻, and 0 for X=imidazole and pyridine) predominantly via dissociative interchange mechanism. The labilizing action of the coordinated sulfite on the trans-Cr^III-X bond in trans-[XCr(Salen)(OSO₂)]⁽ⁿ⁺¹⁾⁻ follows the sequence: NCS⁻pyridine ca. N₃⁻ ca. imidazole. Data analysis indicated that the coordinated sulfite has little trans activating influence. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 373–384, 1998     

A Stereoselective Glycosylation Approach to the Construction of 1,2-trans-β-d-Glycosidic Linkages and Convergent Synthesis of Saponins

Conventional syntheses of 1,2-trans-β-d - or α-l -glycosidic linkages rely mainly on neighboring group participation in the glycosylation reactions. The requirement for a neighboring participation group (NPG) excludes direct glycosylation with (1→2)-linked glycan donors, thus only allowing stepwise assembly of glycans and glycoconjugates containing this type of common motif. Here, a robust glycosylation protocol for the synthesis of 1,2-trans-β-d - or α-l -glycosidic linkages without resorting to NPG is disclosed; it employs an optimal combination of glycosyl N-phenyltrifluroacetimidates as donors, FeCl₃ as promoter, and CH₂Cl₂/nitrile as solvent. A broad substrate scope has been demonstrated by glycosylations with 12 (1→2)-linked di- and trisaccharide donors and 13 alcoholic acceptors including eight complex triterpene derivatives. Most of the glycosylation reactions are high yielding and exclusively 1,2-trans selective. Ten representative, naturally occurring triterpene saponins were thus synthesized in a convergent manner after deprotection of the coupled glycosides. Intensive mechanistic studies indicated that this glycosylation proceeds by S_N2-type substitution of the glycosyl α-nitrilium intermediates. Importantly, FeCl₃ dissociates and coordinates with nitrile into [Fe(RCN)_nCl₂]⁺ and [FeCl₄]⁻, and the ferric cationic species coordinates with the alcoholic acceptor to provide a protic species that activates the imidate, meanwhile the poor nucleophilicity of [FeCl₄]⁻ ensures an uninterruptive role for the glycosidation.     

Minocycline‐Based Europium(III) Chelate Complexes: Synthesis,Luminescent Properties,and Labeling to Streptavidin

Two chelate ligands for europium(III) having minocycline (=(4S,4aS,5aR,12aS)‐4,7‐bis(dimethylamino)‐1,4,4a,5,5a,6,11,12a‐octahydro‐3,10,12,12a‐tetrahydroxy‐1,11‐dioxonaphthacene‐2‐carboxamide; 5 ) as a VIS‐light‐absorbing group were synthesized as possible VIS‐light‐excitable stable Eu³⁺ complexes for protein labeling. The 9‐amino derivative 7 of minocycline was treated with H₆TTHA (=triethylenetetraminehexaacetic acid=3,6,9,12‐tetrakis(carboxymethyl)‐3,6,9,12‐tetraazatetradecanedioic acid) or H₅DTPA (=diethylenetriaminepentaacetic acid=N,N‐bis{2‐[bis(carboxymethyl)amino]ethyl}glycine) to link the polycarboxylic acids to minocycline. One of the Eu³⁺ chelates, [Eu³⁺(minocycline‐TTHA)] ( 13 ), is moderately luminescent in H₂O by excitation at 395 nm, whereas [Eu³⁺(minocycline‐DTPA)] ( 9 ) was not luminescent by excitation at the same wavelength. The luminescence and the excitation spectra of [Eu³⁺(minocycline‐TTHA)] ( 13 ) showed that, different from other luminescent Eu^III chelate complexes, the emission at 615 nm is caused via direct excitation of the Eu³⁺ ion, and the chelate ligand is not involved in the excitation of Eu³⁺. However, the ligand seems to act for the prevention of quenching of the Eu³⁺ emission by H₂O. The fact that the excitation spectrum of [Eu³⁺(minocycline‐TTHA)] is almost identical with the absorption spectrum of Eu³⁺ aqua ion supports such an excitation mechanism. The high stability of the complexes of [Eu³⁺(minocycline‐DTPA)] ( 9 ) and [Eu³⁺(minocycline‐TTHA)] ( 13 ) was confirmed by UV‐absorption semi‐quantitative titrations of H₄(minocycline‐DTPA) ( 8 ) and H₅(minocycline‐TTHA) ( 12 ) with Eu³⁺. The titrations suggested also that an 1 : 1 ligand Eu³⁺ complex is formed from 12 , whereas an 1 : 2 complex was formed from 8 minocycline‐DTPA. The H₅(minocycline‐TTHA) ( 12 ) was successfully conjugated to streptavidin (SA) (Scheme 5), and thus the applicability of the corresponding Eu³⁺ complex to label a protein was established.     

Mono- and bi-metallic complexes based on redox-active tris(3,5-dimethylpyrazolyl)borato-molybdenum nitrosyls,part III.(1) Complexes containing meta-substituted benzene- and naphthalenediols or -diamines

Summary The complexes [MoL^*(NO)Cl(YC₆H₄YH-m)] (Y = O or NH), [MoL^*(NO)Cl(YC₁₀H₆YH-1,5)], (Y = O or NH), [MoL^*(NO)Cl(OC₁₀H₆OH-2,7)], [{MoL^*(NO)Cl}₂(XC₆H₄Y-m)] (X=Y=O, NH or S; X=O, Y=NH), [{MoL^*(NO)-C1}₂(YC₁₀H₆Y-1,5)] (Y=O or NH) and [{MoL^*(NO)Cl₂-(OC₁₀H₆-2,7)] have been prepared and studied by cyclic voltammetry. The monometallic species undergo a reversible oneelectron reduction, whereas the bimetallics undergo two oneelectron reductions. A comparison of E_1/2 (E_1/2(1)-E_1/2(2)) values for those new species with those obtained frompara- substituted analogues and bimetallics containing extended bridges YC₆H₄ZC₆H₄Y (e.g. Z = S or CH₂CH₂) established that the interaction between the redox centres in these new species is intermediate (YC₆H₄Y-m; NHC₁₀H₆NH-1,5) or weak (OC₁₀H₆O).In earlier papers^1,2 we have described the synthesis and electrochemical properties of a series of mono- and bi-metallic complexes of the type [MoL^*(NO)X(YC₆H₄YH)], [MoL^*(NO)X}₂(YC₆H₄Y)] and [{MoL^*(NO)X}₂(YC₆H₄-ZC₆H₄Y)] [L^*=tris(3,5-dimethylpyrazolyl)borate, HB(Me₂C₃HN₂)₃] where the arene ring ispara-substituted (X=Cl or I while Y=O, S or NH and Z = nothing, CH₂, CH₂CH₂, S, SO₂ or O). We have shown that the E_1/2-values of these species are dependent on X and Y, and that the bimetallic species undergo two one-electron reduction processes.We have established that there is strong interaction between the redox centres in bimetallics bridged byp-YC₆H₄Y, but that weak-to-negligible interaction occurs in those species containing YC₆H₄ZC₆H₄Y bridges. In this paper we describe our investigations ofmete-substituted bridging systems,m-YC₆H₄Y, and comparable systems containing naphthalene bridges,e.g. 1,5- or 2,7-YC₁₀H₂Y. From these studies we hoped to establish the extent of interaction between the two redox centres and how this compared to thepara-substituted arene counterparts.     

Nitrite and Nitric Oxide Interconversion at Mononuclear Copper(II): Insight into the Role of the Red Copper Site in Denitrification

Nitrite (NO₂⁻) and nitric oxide (NO) interconversion is crucial for maintaining optimum NO flux in mammalian physiology. Herein we demonstrate that [ L ₂Cu^II(nitrite)]⁺ moieties (in 2 a and 2 b ; where, L = Me₂PzPy and Me₂PzQu ) with distorted octahedral geometry undergo facile reduction to provide tetrahedral [ L ₂Cu^I]⁺ (in 3 a and 3 b ) and NO in the presence of biologically relevant reductants, such as 4-methoxy-2,6-di-tert-butylphenol (4-MeO-2,6-DTBP, a tyrosine model) and N-benzyl-1,4-dihydronicotinamide (BNAH, a NAD(P)H model). Interestingly, the reaction of excess NO gas with [ L ₂Cu^II(MeCN)₂]²⁺ (in 1 a ) provides a putative {CuNO}¹⁰ species, which is effective in mediating the nitrosation of various nucleophiles, such as thiol and amine. Generation of the transient {CuNO}¹⁰ species in wet acetonitrile leads to NO₂⁻ as assessed by Griess assay and ¹⁴N/¹⁵N-FTIR analyses. A detailed study reveals that the bidirectional NO_x-reactivity, namely, nitrite reductase (NIR) and NO oxidase (NOO), at a common Cu^II site, is governed by the geometric-preference-driven facile Cu^II/Cu^I redox process. Of broader interest, this study not only highlights potential strategies for the design of copper-based catalysts for nitrite reduction, but also strengthens the previous postulates regarding the involvement of red copper proteins in denitrification.     

Halogeno-Nitrosylkomplexe von Molybdän und Wolfram. Die Kristallstrukturen von [Na2(15-Krone-5)2(CH3CN)][MoCl4(NO)2] und [Na(15-Krone-5)]2[MoF4Cl(NO)]

Halogeno-Nitrosyl Complexes of Molybdenum and Tungsten. Crystal Structures of [Na₂(15-Crown-5)₂(CH₃CN)][MoCl₄(NO)₂] and [Na(15-Crown-5)]₂[MoF₄Cl(NO)] MoCl₂(NO)₂ and WCl₂(NO)₂, respectively, react with excess sodium fluoride in acetonitrile at room temperature and in the presence of 15-crown-5 to give crystalline mixtures, which consist of the title compounds, respectively of [Na(15-crown-5)]₂[WCl₄(NO)₂] and [Na(15-crown-5)]₂[WF₄Cl(NO)], and which can be separated by selection. The complexes are characterized by their i.r. spectra, the molybdenum compounds additionally by crystal structure determinations. [Na₂(15-crown-5)₂(CH₃CN)][MoCl₄(NO)₂]: Space group P2₁, Z = 2, 5415 independent unique reflexions, R = 0.039. Lattice dimensions at ?10°C: a = 984.3, b = 1231.1, c = 1483.0 pm, β = 105.67°. The compound consists of cations [Ne(l5-crown-5)(CH₃CN)]⁺, in which the sodium ion is surrounded by the five O-atoms of the crown ether and by the N-atom of the acetonitrile molecule, as well as of anions, which form an ion pair {Na(15-crown-5)[MoCl₄(NO)₂]}^?. In the in pairs the sodium ion is coordinated by the five oxygen atoms of the crown ether and by two chlorine atoms of the [MoCI₄(NO)₂]^2? unit. The nitrosyl ligands take the cis-position a t the molybdenum atom which is in a distorted octahedrally fashion. [Na(15-crown-5)]₂[MoF₄Cl(NO)]. Space group C2/c, Z = 4, 1933 independent unique reflexions, R = 0.078. Lattice dimensions at ?7O°C: D : 1.585.8, b = 1171.5, c = 1771.5 pm, β = 114.91°. The compound forms an ion triple, in which the sodium ions are linked to five oxygen atoms each of the crown ether molecules, and to two F-atoms of the [MoF₄Cl(NO)]^2? unit. The F-atom which is arranged in trans-position to the nitrosyl ligand coordinates with both sodium ions; thus an unusual T-shaped arrangement results for this F-atom. The sole terminal F-Atom and the Cl-atom are disordered in two positions.     

The Fe2(NO)2 Diamond Core: A Unique Structural Motif In Non‐Heme Iron–NO Chemistry

Non‐heme high‐spin (hs) {FeNO}⁸ complexes have been proposed as important intermediates towards N₂O formation in flavodiiron NO reductases (FNORs). Many hs‐{FeNO}⁸ complexes disproportionate by forming dinitrosyl iron complexes (DNICs), but the mechanism of this reaction is not understood. While investigating this process, we isolated a new type of non‐heme iron nitrosyl complex that is stabilized by an unexpected spin‐state change. Upon reduction of the hs‐{FeNO}⁷ complex, [Fe(TPA)(NO)(OTf)](OTf) ( 1 ), the N‐O stretching band vanishes, but no sign of DNIC or N₂O formation is observed. Instead, the dimer, [Fe₂(TPA)₂(NO)₂](OTf)₂ ( 2 ) could be isolated and structurally characterized. We propose that 2 is formed from dimerization of the hs‐{FeNO}⁸ intermediate, followed by a spin state change of the iron centers to low‐spin (ls), and speculate that 2 models intermediates in hs‐{FeNO}⁸ complexes that precede the disproportionation reaction.     

Kinetic study of the ligand substitution on the trimethylplatinum(iv) complexes with unidentate ligands

Ligand substitution kinetics for the reaction [Pt^IVMe₃(X)(NN)]+NaY=[Pt^IVMe₃(Y)(NN)]+NaX, where NN=bipy or phen, X=MeO⁻, CH₃COO⁻, or HCOO⁻, and Y=SCN⁻ or N₃⁻, has been studied in methanol at various temperatures. The kinetic parameters for the reaction are as follows. The reaction of [PtMe₃(OMe)(phen)] with NaSCN: k₁=36.1±10.0 s⁻¹; ΔH₁^≠=65.9±14.2 kJ mol⁻¹; ΔS₁^≠=6±47 J mol⁻¹ K⁻¹; k₋₂=0.0355±0.0034 s⁻¹; ΔH₋₂^≠=63.8±1.1 kJ mol⁻¹; ΔS₋₂^≠=−58.8±3.6 J mol⁻¹ K⁻¹; and k₋₁/k₂=148±19. The reaction of [PtMe₃(OAc)(bipy)] with NaN₃: k₁=26.2±0.1 s⁻¹; ΔH₁^≠=60.5±6.6 kJ mol⁻¹; ΔS₁^≠=−14±22 J mol⁻¹K⁻¹; k₋₂=0.134±0.081 s⁻¹; ΔH₋₂^≠=74.1±24.3 kJ mol⁻¹; ΔS₋₂^≠=−10±82 J mol⁻¹K⁻¹; and k₋₁/k₂=0.479±0.012. The reaction of [PtMe₃(OAc)(bipy)] with NaSCN: k₁=26.4±0.3 s⁻¹; ΔH₁^≠=59.6±6.7 kJ mol⁻¹; ΔS₁^≠=−17±23 J mol⁻¹K⁻¹; k₋₂=0.174±0.200 s⁻¹; ΔH₋₂^≠=62.7±10.3 kJ mol⁻¹; ΔS₋₂^≠=−48±35 J mol⁻¹K⁻¹; and k₋₁/k₂=1.01±0.08. The reaction of [PtMe₃(OOCH)(bipy)] with NaN₃: k₁=36.8±0.3 s⁻¹; ΔH₁^≠=66.4±4.7 kJ mol⁻¹; ΔS₁^≠=7±16 J mol⁻¹K⁻¹; k₋₂=0.164±0.076 s⁻¹; ΔH₋₂^≠=47.0±18.1 kJ mol⁻¹; ΔS₋₂^≠=−101±61 J mol⁻¹ K⁻¹; and k₋₁/k₂=5.90±0.18. The reaction of [PtMe₃(OOCH)(bipy)] with NaSCN: k₁ =33.5±0.2 s⁻¹; ΔH₁^≠=58.0±0.4 kJ mol⁻¹; ΔS₁^≠=−20.5±1.6 J mol⁻¹ K⁻¹; k₋₂=0.222±0.083 s⁻¹; ΔH₋₂^≠=54.9±6.3 kJ mol⁻¹; ΔS₋₂^≠=−73.0±21.3 J mol⁻¹ K⁻¹; and k₋₁/k₂=12.0±0.3. Conditional pseudo-first-order rate constant k₀ increased linearly with the concentration of NaY, while it decreased drastically with the concentration of NaX. Some plausible mechanisms were examined, and the following mechanism was proposed. [Note to reader: Please see article pdf to view this scheme.] © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 523–532, 1998     

Synthesis and X-ray and Spectral Study of the Compounds [Q4N]2[Fe2(S2O3)2(NO)4] (Q = Me,Et, n-Pr,n-Bu)

Iron nitrosyl complexes with general formula [Q₄N]₂[Fe₂(S₂O₃)₂(NO)₄] (Q = Me, Et, n-Pr, n-Bu) were synthesized by the exchange reaction of K₂[Fe₂(S₂O₃)₂(NO)₄] with tetraalkylammonium bromides. The molecular and crystal structure of [(CH₃)₄N]₂[Fe₂(S₂O₃)₂(NO)₄] were studied by X-ray diffraction analysis. The iron atom in the four-membered cycle of the [2Fe–2S] anion is bound to another Fe atom and to two sulfur atoms and is coordinated by two nonequivalent NO groups, each bridging sulfur atom being bound to the SO₃group. The structurally equivalent iron atoms are in the state Fe^1–(S= 1/2). The Mössbauer spectroscopy method shows that the complexes are diamagnetic due to the strong Fe–Fe bond. It is found that the SO₃group provides higher stability of the thiosulfate anion than the anion in Roussin's red salt [Fe₂S₂(NO)₄]^2–.