Kinetics and mechanism of nucleophilic substitution of dichloro{1-methyl-2-(arylazo)imidazole}palladium(II) by pyridine bases

The reaction of dichloro{1-methyl-2-(arylazo)imidazole}palladium(II), Pd(RaaiMe)Cl₂ where RaaiMe = p-R–C₆H₄N=N–C₃H₂N₂-1-Me; R = H(1), Me(2), Cl(3), with pyridine bases [RPY: R = H (a), 4-Me (b), 4-Cl (c), 2-Me (d), 2,6-Me₂ (e), 2,4,6-Me₃ (f)] has been studied spectrophotometrically in MeCN at 451 nm. The products (4) have been isolated and characterised as trans-Pd(RPy)₂Cl₂. The kinetics of the nucleophilic substitution has been examined under pseudo-first-order conditions at 298 K. A single phase reaction step has been observed for bases such as Hpy (a), 4-MePy (b) and 4-ClPy (c) and follows the rate law: rate = (a + k[RPy]²[Pd(RaaiMe)Cl₂]). The bases 2-MePy (d), 2,6-Me₂Py (e) and 2,4,6-Me₃Py (f) exhibits a bi-phasic reaction and follows the rate laws: rate–1 = (a + k[RPy][Pd(RaaiMe)Cl₂]) and rate–2 = (a + k[RPy][Pd(RaaiMe)-Cl₂]), where k is the third-order rate constant; k is the second-order first phase rate constant, k is the second-order second phase rate constant and a/a/a correspond to the solvent dependent constant of the respective reaction path. The rate data supports a nucleophilic association path. External addition of Cl^– (LiCl) suppresses the rate, which follows the order: k/k/k (3) > k/k,k (1) > k/k,k (2). The k values are linearly related to the Hammett constants. The 2-substituted pyridines (d–f) remarkably reduce the rate and show a bi-phasic reaction behaviour as compared with 4-Rpy (a–c). This is attributed to the steric effect that destabilises the transition state. The rate decreases with increasing steric crowding at the ortho-position and follows the order: (d) > (f) > (e). The 4-substituted pyridines control the rate via an inductive effect and follow the order: (b) > (a) > (c).     

A new spot test reagent for chromium(VI), vanadium(V), and hexacyanoferrate(III) ions: the schiff base from 4,4′-methylenedianiline and 4-dimethylaminobenzaldehyde

Summary A new Schiff base, bis(4-dimethylaminobenzylidine)4,4-methylenedianiline (I) has been prepared by reacting 4-dimethylaminoben-zaldehyde with 4,4-methylenedianiline. A 1% solution ofI in conc. sulphuric acid gives a deep red or blood red colour with Cr(VI), and V(V), and a deep rose red colour with [Fe(CN)₆]^3-. The limits of detection and dilution are 0.7 g, 171,000 for Cr(VI); 5 g, 110,000 for V(V); and 7 g, 17,100 for [Fe(CN)₆]^3-. Cr(III), V(IV), and [Fe(CN)₆]^4- do not interfere. The effects of common anions and cations are reported.

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Zusammenfassung Durch Umsetzung von 4-Dimethylaminobenzaldehyd mit 4,4-Methylen-dianilin wurde eine neue Schiffsche Base hergestellt, deren 1%ige Lösung in konz. Schwefelsäure eine tiefrote oder blutrote Farbe mit Cr(VI) und V(V), eine tiefrosa Farbe mit [Fe(CN)₆]^3– gibt. Die Nachweisgrenzen bzw. die Grenzkonzentrationen betragen: 0,7 g, 171000 für Cr(VI), 5 g, 110000 für V(V) und 7 g, 17100 für [Fe(CN)]₆ ^3–. Cr(III), V(IV) und [Fe(CN)₆]^4– stören nicht. Der Einfluß gängiger Anionen und Kationen wird angegeben.

     

Kinetics and mechanism of the hydrolysis of sodium carboxymethylcellulose (Na-CMC) by a cellulase complex

TheSomogyi-Nelson colorimetric method is applied in a new manner more suitable for evaluating the kinetics of the enzyme hydrolysis of sodium carboxymethylcellulose (Na-CMC) catalyzed by the cellulase complex. By means of selective inhibition of a chosen enzyme from the cellulase complex it became possible to trace the effect of the other enzymes included in its composition.

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Kinetik und Mechanismus der Hydrolyse von Natriumcarboxymethylcellulose (Na-CMC) durch einen Cellulase-Komplex

Zusammenfassung Die kolorimetrische Methode nachSomogyi undNelson wird nach einem neuen Verfahren zur Verfolgung der Kinetik der hydrolytischen Spaltung von Natriumcarboxymethylcellulose (Na-CMC), katalysiert durch den Cellulase-Komplex, angewandt. Durch selektive Inhibierung eines bestimmten Enzyms des Cellulase-Komplexes kann man die Wirkung der anderen zu seiner gesamten Zusammensetzung gehörenden Enzyme verfolgen.

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Symbols Used E enzyme (E—cellulase;E—exo-cellobiohydrolase;E—-glucosidase) - [E] _w weight concentration of enzymeE - S substrate (Na-CMC—sodium carboxymethylcellulose) - [S]₀ weight concentration of substrateS - I inhibitor (I—lactose;I—calcium chloride;I—condurrite-B-epoxide) - P product (P—oligosaccharides;P—cellobiose;P—D-glucose) - P end product (K , K , K ) - DP degree of polymerization - DS degree of substitution - ES enzyme-substrate complex (E S, E S, E S) - EP enzyme-product complex (E P, E P) - EI enzyme-inhibitor complex (E I, E I, E I) - M _s molecular mass of substrateS - K _s substrate constant (K _s , K _s , K _s ) - K _I inhibitor constant (K _I , K _I , K _I ) - K _m Michaelis-Menten constant - k ₊₁,k ₊₂ (k ₊₂ ,k ₊₂ ,k ₊₂ ) forward rate constants - k _–1 reverse rate constant - ₀ initial rate of reaction - V maximal reaction rate - A change in absorbance - molar absorption coefficient - wavelength Herrn Prof. Dr.Hans Tuppy zum 60. Geburtstag herzlichst gewidmet.     

Salicylaldehydo chelates of bis(cyclopentadienyl) zirconium(IV)

A new series of organometallic ionic chelates of the type [Cp ₂Zr(sal)]⁺ [ROCS₂/RRNCS₂]^–, where Hsal = salicylaldehyde;R =Me, Et, i-Pr ori-Bu andR =R =Me, Et, i-Pr;R =Me,R = benzyl orR =Et,R =m-tolyl, have been synthesized in aqueous medium by the reaction of [Cp ₂Zr(sal)]⁺Cl^– andROCS ₂ ^– K⁺/RRNCS ₂ ^– Na⁺. These compounds have been characterized by chemical analyses, electrical conductance, electronic, IR and¹H-NMR spectral studies. These studies indicate that the complexes are 1:1 electrolytes and the salicylaldehyde ligand is chelating in all these complexes. Therefore, a tetrahedral coordination about the zirconium atom is proposed.

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Salicylaldehydo-Chelate von Bis(cyclopentadienyl)-zirkonium(IV)

Zusammenfassung Eine neue Gruppe von organometallischen ionischen Chelaten vom Typ [Cp ₂Zr(sal)]⁺ [ROCS₂/RRNCS₂]^– (mit Hsal = Salicyladehyd;R =Me, Et, i-Pr oderi-Bu undR =R =Me, Et, i-Pr;R =Me,R = Benzyl oderR =Et,R =m-Tolyl) wurde in wäßrigem Medium mittels der Reaktion von [Cp ₂Zr(sal)]⁺Cl^– mitROCS ₂ ^– K⁺/RRNCS ₂ ^– Na⁺ hergestellt. Die erhaltenen Verbindungen wurden mittels chemischer Analyse, elektrischer Leitfähigkeit und der IR- sowie¹H-NMR-Spektren charakterisiert. Diese Untersuchungen zeigen, daß die Komplexe 1:1-Elektrolyte sind, wobei der Salicylaldehyd-Ligand in allen Fällen an der Chelatbildung beteiligt ist. Es wird daher für das Zirkoniumatom eine tetrahedrale Koordination vorgeschlagen.

     

Kinetics and mechanism of osmium(VIII)-catalysed and uncatalysed oxidation of aminoalcohols by chloramine-T in alkaline medium

Summary The kinetics of osmium(VIII)-catalysed oxidation of aminoalcohols,viz., 2-aminoethanol, 3-aminopropanol, diethanolamine and triethanolamine, by chloramine-T in alkaline medium have been investigated. The reactions follow a first-order-rate dependence with respect to oxidant. The order in [aminoalcohol] decreases from unity at higher concentrations of aminoalcohols while that in [OH^–] is nearly –1. The oxidation rate is directly proportional to [osmium(VIII)] in primary amino-alcohols, while that is proportional to {k+k [osmium(VIII)]} (where k and k are rate constants) in diethanolamine and triethanolamine. The uncatalysed oxidation of diethanolamine and triethanolamine follows a first-order-rate dependence in each of the oxidant and the sustrate. Suitable mechanisms consistent with the observed kinetic results are proposed.     

The unusual morphological structure of the aging products of coprecipitated Fe(III)-Al(III) hydroxides

Aluminum-substituted hematite ( ^*-Fe₂O₃) with an unusual morphological structure is formed upon the aging of coprecipitated Fe(III)-Al(III) hydroxides with excess Fe(III). The crystals of this hematite are found in separate layers and includes seams of an aluminum-containing phase. In samples with excess Al(III) content, the ^*-Fe₂O₃ crystals are found as seams in mixed aggregates of boehmite and ^*-Fe₂O₃.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 931–933, April, 1990.     

Novel dioximato-bridged chromium(III)-copper(II)-chromium(III) trinuclear complexes with ferromagnetic exchange interactions

Summary Two new dioximato-bridged trinuclear Cr^II-Cu^II-Cr^III complexes, [Cr(salen)-Cu(-BD)₂-Cr(salen)] (1) and [Cr(salen)-Cu(-FD)₂-Cr(salen)]-H₂O (2), have been prepared and characterized [salen^2– = N,N-ethylene- bis (salicylideneiminate), (-BD)^2– = -benzyldioximato and (-FD)^2– = -furildioximato]. Magnetic susceptibility measurements in the 4.2–300 K range demonstrated the operation of a ferromagnetic interaction between the adjacent Cr^III and Cu^II ions through oximato bridges in both (1) and (2). Based on spin Hamiltonians =–2J(₁₂+₂₃)(S₁=S₃=3/2,S₂=1/2) the exchange integrals (J) were evaluated as 3.19 and 5.38 cm^–1 for (1) and (2), respectively.     

Phenolate complexes of iron(III) in dimethylsulphoxide solution

Summary The formation of complexes between Fe³⁺ and 2,4-dinitrophenol, 4-nitrophenol and 4-methylphenol is studied in dimethylsulphoxide solution. The reaction proceeds almost to completion and the occurrence, in solution, of complexes with higher stoichiometry than 11 is reported for the first time. The following stability constants are determined (25 °C, 0.1 M KClO₄): Fe^III-2,4-dinitrophenolate ₁=1.8×10³, ₂=4.4×10⁵; Fe^III-4-nitrophenolate ₁=1.10×10⁷, ₂=2.5×10¹² ₃=3.9×10¹⁶; Fe^III-4-methylphenolate =1.7×10¹².The binding of a phenolate ligand to iron(III) strongly decreases its affinity for other phenolate ligands. The superior -donor, 4-methylphenolate (OC₆H₄Me)^–, only forms a 11 complex, Fe(OC₆H₄Me)²⁺. The e.s.r. spectrum of this species clearly prove it is a true iron(III) complex and does not contain iron(II), in opposition to recent claims. However, the complex Fe(OC₆H₄Me)²⁺ easily undergoes a ligand-to-metal electron transference. Addition of an excess of 1,10 phenanthroline yields the iron(II) complex [Fe(o-phen)₃]²⁺ instantaneously.     

Kinetics and mechanism of dissociation of ethylenedibiguanidenickel(II) and copper(II) and of bisbiguanide-nickel(II) in acid

Summary The kinetics of dissociation of the ethylenedibiguanidenickel(II) and copper(II), [M(EndibigH₂)]²⁺, where M = Ni^II or Cu^II, and bisbiguanide-nickel(II), [Ni(BigH)₂]²⁺, complexes in acid media forming the aquo-metal ions and the protonated ligand as the ultimate products have been studied by the stopped-flow technique. The reactions occur in two consecutive steps, the first being faster than the second, forming aquometal ions and protonated ligands as the ultimate products. For each step the rate is acid dependent and may be expressed by: k_x = k _x [H⁺] + k _x [H⁺]², where k_x is the observed rate constant and x = f or s for fast and slow steps respectively. Both paths (k _x and k _x ) contribute in the ethylenedibiguanidenickel(II) system, whereas k _x paths are virtually absent in the corresponding copper(II) complex; k _x paths are absent in the bisbiguanidenickel(II) system. A likely mechanism involves protonation of the bound ligand which facilitates its dissociation. A comparison of the S values indicates considerable solvent participation in the transition state, suggesting an assisted dissociative mechanism, which also accounts for the low H values. The observed lability order is [Ni(EndibigH₂)]²⁺ < [Ni(BigH)₂]²⁺ =ca. [Cu(EndibigH₂)]²⁺, and [Cu(BigH)₂]²⁺ dissociates under comparable conditions at a rate too fast to be measured by the stopped-flow method.     

Mössbauer studies of thermal decomposition of metal(III) hexacyanoferrates(II)

The thermal decomposition of metal(III) hexacyanoferrates(II) (Al, As, Sb, Bi) was studied up to 700° in air by employing Mössbauer, infrared spectroscopy and thermal analysis techniques. With the exception of the bismuth compound, the isomer shift of these hexacyanoferrates(II) increases on dehydration at 200°. Dehydration is complete at 200°, decomposition into the ferrite at 300°, and formation of-Fe₂O₃ from aluminium and bismuth hexacyanoferrates(II) and Fe₃O₄ from antimony and arsenic hexacyanoferrates(II) at 700°.

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Zusammenfassung Die thermische Zersetzung von Metall(III)ferrocyaniden (Al, As, Sb, Bi) wurde bis zu 700° in Luft unter Anwendung der Mössbauer und Infrarotspektroskopie, sowie thermoanalytischer Techniken untersucht. Die Isomerverschiebung dieser Ferrocyanide nimmt mit der Dehydratisierung bei 200° zu, mit Ausnahme des Wismuts. Die Dehydratisierung ist bei 200° abgeschlossen, die Zersetzung zum Ferrit bei 300° und die Bildung von-Fe₂O₃ aus Aluminium- und Wismutferrocyanid, von Fe₃O₄ aus Antimon- und Arsenferrocyanid bei 700°.

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Résumé On a étudié dans l'air jusqu'à 700°, la décomposition thermique des ferrocyanures de métaux trivalents (Al, As, Sb, Bi), par spectroscopies Mössbauer et infrarouge, ainsi que par les techniques d'analyse thermique. Le déplacement des isomères de ces ferrocyanures augmente lors de la déshydratation à 200°, à l'exception du bismuth. La déshydratation est complète à 200°, la décomposition en ferrite à 300°, la formation d'-Fe₂O₃ à partir des ferrocyanures d'aluminium et de bismuth ainsi que du Fe₃O₄ à partir des ferrocyanures de l'antimoine et de l'arsenic à 700°

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-, , — Al, As, Sb, Bi- 700° . , , 200°. 200°, 300° -Fe₂O₃. 700° Fe₃O₄.

     

Synthesis and magnetic properties of trinuclear chromium(III)palladium(II)-chromium(III) complexes bridged by extended dioximato groups

Summary Heterotrinuclear Cr^III-Pd^II-Cr^III complexes of formulae [Cr(salen)-Pd(dmg)₂-Cr(salen)]·H₂O (1), [Cr(salen)-Pd(-BD) ₂-Cr(salen)]·H₂O (2) and [Cr(salen)-Pd(-FD) ₂-Cr(salen)]·2H₂O (3) [dmg^2- =dimethyl-glyoximato, (-BD)^2/2- = -benzyldioximato, (-FD)^2/2- = -furildioximato and salen^2– = N,N-ethylenebis(salicylideneiminate)] have been prepared and characterized by elemental analysis, i.r. and electronic spectroscopies, and molar conductances. These complexes are thought to contain extended diomixato bridges. The magnetic properties of complex (1) has been investigated over the 80–300 K range and corresponds to what is expected for an antiferromagnetic Cr^III-Cr^IIIi pair with S _Cr = 3/2 and S _Pd = 0 (Pd²⁺ is a diamagnetic in a square-planar environment) local spins. The exchange integral (J) was evaluated as -3.38cm^–1 using the spin Hamiltonians = -2J _{A B}(S _A = S _B = 3/2).     

Some compounds of iron(III) with tertiary and secondary nitrogen bases

Summary The iron(III) compound, FeCl(OH)(MeCO₂) · MeCO₂ H · 0.5 H₂O, combines with tertiary nitrogen bases, pyridine, quinoline and-picoline, to form FeCl(OH)(MeCO₂) · (Base) 0.5 H₂O and with-picoline to give FeCl(OH)(MeCO₂) (-picoline). The secondary nitrogen bases (BH), such as, piperidine, pyrrolidine and diethylamine, on the other hand, react with the elimination of base hydrochloride to form Fe(B)(OH)(MeCO₂) · 0.5 H₂O compounds, containing covalently bonded bases. Pyrrole and indole (BH) combine with the partial elimination of chlorine to give Fe₃Cl₂(B)(OH)₃(MeCO₂)₃ · 3(BH). Phthalimide (BH), however, forms a simple addition compound Fe₂Cl₂(OH)₂(MeCO₂)₂ · (BH). The i.r. spectra, room temperature magnetic susceptibilities, thermal decompositions wherever possible and molar conductance have been studied.     

Thermal decomposition of halo-bis(piperidyldithio-carbamates) of As(III), Sb(III) and Bi(III)

Simultaneous TG/DTG/DTA studies under non-isothermal conditions have been carried out in air and nitrogen on some halo-dithiocarbamates of the general formula XM[S₂CN(CH₂)₅]₂ (X=Cl, Br and I; andM=As, Sb and Bi).E* values for the 1st stage of decomposition were determined by graphical methods and the TTN temperatures were calculated from the TG profiles. A possible mechanism of the decomposition reaction is suggested, based on the thermoanalytical and pyrolysis results and the mass spectral data. The kinetic analysis data on five of the above dithiocarbamates and nine complexes of the general formula M[S₂CN<]₃ (M=As, Sb and Bi; and N<=NEt₂, N(CH₂)₅ and N(CH₂)₄O) were studied by the QIA (quasi-isothermal analysis) technique in air atmosphere. An example of kinetic parameter (k andn) estimation for the first decomposition stage is given for Bi[S₂CN(CH₂)₅]₃, with the assumption of different kinetic equations.

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Zusammenfassung Einige helo-Dithiocarbamate der allgemeinen Formal XM[S₂CN(CH₂)₅]₂ (X=Cl, Br und I;M=As, Sb und Bi) wurden mittels simultaner TG/DTG/DTA unter nichtisothermen Bedingungen in Luft und Stickstoff untersucht. Für den ersten Zersetzungsschritt wurden E^*-Werte durch graphische Methoden bestimmt und die TIN-Temperaturen aus den TG-Profilen berechnet. Ein auf den Ergebnissen der Thermogravimetrie und Pyrolyse sowie auf massenspektroskopischen Daten beruhender möglicher Mechanismus wird vorgeschlagen. Fünf der angeführten Dithiocarbamate und 9 Komplexe der allgemeinen Formel M[S₂CN<]₃] (M=As, Sb und Bi;N=NEt₂, N(CH₂)₅ und N(CH₂)₄O) wurden mittels QIA (quasi-isotherme Analyse) in Luft untersucht. Als Beispiel ist die Bestimmung der kinetischen Parameter (k undn) für den ersten Schritt der Zersetzung von Bi[S₂CN(CH₂)₅]₃ unter Annahme verschiedener kinetischer Gleichungen angegeben.

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, - XM[S₂CN(CH₂)₅]₂, =Cl, r l, a M=As, Sb Bi. ^a , -. - . M[S₂CN<]₃, M=As, Sb Bi, a N<=NEt₂, N(CH₂)₅ N(CH₂)₄O. k ³[S₂N(₂)₅]₃.

     

Dynamics of the formation and decay of C2(a 3II u,v″=0) radical in a pulse discharge in methane

The plasma of a pulse discharge (0.05 J/cm³) in methane at low pressure (200 Pa) is studied. The dynamics of formation and decay of C₂(a³II_u, v=0) is monitored using a stroboscopic laser absorption method. It was found that substantial amounts of C₂, 10¹⁵ cm^–3, arise with a 1-µs delay after the current pulse.Notation _v absorption coefficient - wave number, cm^–1 - e electron charge - c velocity of light - h Planck's constant - m _e mass of electron - N _v concentration of molecules in the vibrational level v - f oscillator strength - l plasma column length - q _vv Franck-Condon factor - S _JJ Hönl-London factor - Q _rot rotational partition function - F(J) rotational term, cm^–1 - I _sig signal beam intensity - I _ref reference beam intensity - higher state index - lower state index - decay constant     

Simultaneous flow injection speciation of iron(II) and iron(III) cyano complexes utilizing electrochemical and atomic absorption detectors in series

Summary A method is described for the simultaneous speciation of Fe(CN) ₆ ^4– and Fe(CN) ₆ ^3– in a flow injection (FIA) system comprising electrochemical (EC) and flame atomic absorption spectrometry (AAS) detectors in series. One of these species is detected amperometrically at a Pt-electrode by applying the required potential and measuring the resulting reduction or oxidation current of the appropriate iron cyanide complex. Total iron in both species is determined by an AAS detector. The EC detector is inherently more sensitive, with a detection limit of 0.5 g Fe l^–1 and a relative standard deviation of 1.0% for a 0.040 g Fe ml^–1 sample. The limit of detection for the AAS detector is 0.5 g Fe ml^–1, and the relative standard deviation for a 5.70 g Fe ml^–1 sample is 0.40%. The method enables up to 60 analyses (120 speciations) per hour and obviates the problem of easy oxidation of Fe(CN) ₆ ^4– .

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Simultane Speziation von Eisen(II)- und Eisen(III)-Cyanokomplexen durch Flie\injektionsanalyse mit Hilfe von hintereinander geschalteten elektrochemischen und AAS-Detektoren

     

Half-sandwich metal diselenolate complexes Cp#M(NO)(SePh)2 (M = Mo or W; Cp# = Cp or MeCp) as ligands. Synthesis of selenolate-bridged heterobimetallic compounds

The reactions of half-sandwich diselenolate Mo and W complexes Cp^#M(NO)(SePh)₂ (M = Mo; Cp^# = Cp (1a), MeCp (1b); M = W; Cp^# = Cp (1c)) with (Norb)Mo(CO)₄, Ni(COD)₂ and Fe(CO)₅ have been investigated. Treatment of (1a), (1b) and (1c) with (Norb)Mo(CO)₄ in PhMe gave the bimetallic complexes: CpMo(NO)(-SePh)₂Mo(CO)₄ (2a), MeCpMo(NO)(-SePh)₂Mo(CO)₄ (2b) and CpW(NO)(-SePh)₂Mo(CO)₄ (2c) in moderate yields. Irradiation of (1a) and (1c) in the presence of Fe(CO)₅ gave heterobimetallic complexes CpMo(CO)(-SePh)₂Fe(CO)₃ (3a) and CpW(NO)(-SePh)₂Fe(CO)₃ (3c). Ni(COD)₂ reacts with two equivalents of (1a), (1b) and (1c) to give [CpMo(NO)(-SePh)₂]₂Ni (4a), [MeCpMo(NO)(-SePh)₂]₂Ni (4b) and [CpW(NO)(-SePh)₂]₂Ni (4c) in good yields. The new heterobimetallic complexes were characterized by i.r., ¹H-n.m.r., ¹³C-n.m.r. and EI-MS spectroscopy.     

Kinetics and mechanism of dissociation of some tri- and tetra-dentate complexes of copper(II) in acid media

Summary Kinetics of the dissociation ofm-phenylene-dibiguanidecopper(II) ion,N-salicylideneglycyl-glycinatocuprate(II) ion andN-salicylideneglycinato-aquocopper(II) in acid media, forming aquo-copper(II) ion, have been studied by the stopped-flow spectrophotometric technique. Dissociation of the complexes occurs in two consecutive steps, the first being faster than the second. For them-phenylenedibiguanide complex each step exhibits second order acid dependance,k _x=k _x [H⁺]² wherek _x is the observed pseudo-first order rate constant. However, the Schiff base complexes show first order acid dependance,k _x=k _x [H⁺], for both steps. The results, with relatively low H and highly negative S values, are consistent with a solvent-assisted dissociative process.     

Eigenvalues of the real generalized eigenvalue equation perturbed by a low-rank perturbation

The low-rank perturbation (LRP) method solves the perturbed eigenvalue equation (B +V) _k = _k (C +P) _k , where the eigenvalues and the eigenstates of the related unperturbed eigenvalue equationB _i = _i C _i are known. The method is designed for arbitraryn-by-n matricesB, V, C, andP, with the only restriction that the eigenstates _i of the unperturbed equation should form a complete set. We consider here a real LRP problem where all matrices are Hermitian, and where in addition matricesC and (C +P) are positive definite. These conditions guarantee reality of the eigenvalues _k and _i . In the original formulation of the LRP method, each eigenvalue _k is obtained iteratively, starting from some approximate eigenvalue _k . If this approximate eigenvalue is not well chosen, the iteration may sometimes diverge. It is shown that in the case of a real LRP problem, this danger can be completely eliminated. If the rank of the generalized perturbation {V, P} is small with respect ton, then one can easily bracket and hence locate to any desirable accuracy the eigenvalues _k (k = 1, ...,n) of the perturbed equation. The calculation of alln eigenvalues requiresO(² n ²) operations. In addition, if the perturbation (V, P) is local with the localizabilityl p, then onlyO(² n) operations are required for a derivation of a single eigenvalue.     

Reactivity and solvatochromism of 2,2′-bi(4H-5,6-dihydrothiazine)-tetracarbonylmolybdenum(O)

Summary The dependence of the charge-transfer frequency for [Mo(CO)₄(btz)], btz = 2,2-bi(4H-5,6-dihydrothiazine), on solvent is described, and the solvatochromic behaviour of this compound compared with that of other [Mo(CO)₄(LL)] species, with LL = 2,2-bipyrimidine or 2,2-bipyridine, and of iron(II) analogues [Fe(btz)₂(CN)₂] and [Fe(bipy)₂(CN)₂]. Kinetics of solvolysis (k, H, S) are reported for [Mo(CO)₄(btz)] in methanol, acetonitrile, and dimethyl sulphoxide. These kinetic results are analysed into initial state and transition state contributions. A parallel analysis of the solvatochromic results for [Mo(CO)₄(btz)] into ground state and excited state solvation contributions is compared with similar analyses for the solvatochromic organic compoundsp-nitroanisole and dimethylindoaniline.