X-ray photoelectron spectra of tetraaza macrocyclic complexes of cobalt with molecular oxygen

X-ray photoelectron spectroscopy has been used to determine the electronic state of the cobalt-molecular-oxygen fragment, the type of coordination, and, in some cases, the nature of the bond between the central ion and the axial ligand in the complexes [Co^II(htd)(NCS))C10₄, [-O₂{Co(htd((X)}₂](ClO₄)₂ (X=NCS^–, N₃ ^–, NCO^–, OH^–), and [O₂{Co(htd)(Im)}₂](ClO₄)₄. It has been established that the NCO^– and NCS^– ligands are coordinated as electron donors in an axial position by means of their nitrogen atoms. A conclusion regarding the electronic structure of the Co^III-O₂ ^2–-Co^III fragment has been drawn on the basis of an analysis of the binding energy (E_b) of the Co 2p_3/2 electrons in the oxygenated complexes and in the corresponding low-spin cobalt(II) compounds and cobalt(III) compounds.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 4, pp. 437–442, July–August, 1990.     

A new convenient method for the synthesis of mixed-ligand β-diketonato Tc(III) complexes

A new convenient method has been proposed to synthesize mixed-ligand -diketonato Tc(III) complexes, using the ligand exchange reaction [Tc(acac)₂(CH₃CN)₂]⁺+L^–[Tc(acac)₂L]+ +2CH₃CN where L is bza, dpm or dbm. The yield was about 30–40%. UV-visible and IR spectra of these complexes were measured. Characteristic features of the compounds were compared with those of the corresponding complexes of ruthenium.     

Interaction of bivalent transition metal ions with iminodiacetato-(pentaammine/tetraammine)cobalt(III) ions. A kinetic and equilibrium study

Summary The kinetics of reversible complexation of Ni^II and Co^II with iminodiacetato(pentaammine)cobalt(III), [(NH₃)₅-Co(idaH₂)]³⁺ and Ni^II with iminodiacetato(tetraammine)-cobalt(III), [(NH₃)₄Co(idaH)]²⁺, have been investigated by the stopped-flow technique at 25 °C, pH = 5.7–6.9 and I = 0.3 mol dm ^–3. The reaction paths (NH₃)₅Co(idaH)²⁺+M²⁺(NH₃)₅Co(ida)M³⁺+H⁺ (NH₃)₅Co(ida)⁺+M²⁺(NH₃)₅Co(ida)M³⁺ (NH₃)₄Co(ida)⁺+Ni²⁺(NH₃)₄Co(ida)Ni³⁺ have been identified (idaH = N⁺H₂(CH₂CO₂)₂H, ida = NH(CH₂COO)^2–]. The rate parameters for the formation and dissociation of the binuclear species are reported. The data are essentially consistent with an I _d mechanism. The dissociation rate constants of the binuclear species indicate that Ni²⁺ and Co²⁺ are chelated by the coordinated iminodiacetate moiety.     

Novel properties of molecular assemblies of isoprenoid surfactants

Unlike micelles of straight hydrocarbon chain-surfactants, isoprenoid surfactants, CH₃ [CH(CH₃)CH₂CH₂CH₂]₃ CH(CH₃)CH₂–R (R=CH₂N⁺ (CH₃)₃ Br^–, CH₂OPO₃H^– Na⁺, CH₂OSO ₃ ^– Na⁺, CO ₂ ^– Na⁺), gave large globular and cellular assemblies in water which could be observed directly by transmission electron microscopy; critical micelle concentration of 0.31.4×10^–3 M at 20°C, aggregation number of 215×10⁴, and diameter of 200–2000 Å. A basic structure of the assemblies was a thin layer with a thickness (about 30 Å) which was close to the molecular length of the surfactants. The assemblies were decomposed during gel column chromatography; viz., they were not as stable as the liposomes of lecithins. The morphology was discussed in conjunction with a steric effect of the isoprenoid chain.     

Calculs non empiriques sur une réaction SN2 typique

Résumé On a calculé la structure électronique de l'état initial et de l'état de transition de la réaction de substitution F^–+CH₃FFCH₃+F^– par la méthode des orbitales moléculaires SCF dans l'approximation gaussienne. On trouve que l'énergie de l'état de transition est inférieure à la somme des énergies des produits séparés CH₃F et F^–. Cependant, cette contribution négative à l'énergie d'activation est contrebalancée par la variation des énergies de solvatation.

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Ab initio calculations on a typical SN₂ ReactionElectronic structure of methyl fluoride and of the transition state (FCH₃F)^–

The electronic structure of the initial and transition states of the substitution reaction F^–+CH₃F FCH₃+F^– have been calculated by the SCF molecular orbital method in the Gaussian approximation. It is found that the energy of the transition state is lower than the sum of the energies of the separated systems CH₃F and C^–. However, this negative contribution to the activation energy is balanced by the variation of solvatation energies.

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Zusammenfassung Die Elektronenstruktur des Ausgangs- und des Übergangszustandes der Substitutionsreaktion F^–+CH₃FFCH₃+F^– wurden mit einer SCF-MO-Methode mit Gaußfunktionen berechnet. Die Energie des Übergangszustandes ist niedriger als die Summe der Energien der separierten Systeme CH₃F und F^–. Dieser negative Beitrag zu der Aktivierungsenergie wird allerdings ausgeglichen durch eine Änderung der Solvatationsenergie.

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Remerciements. Nous remercions bien sincèrement M. A. Rassat (CEN, Grenoble) de nous avoir suggéré ce problème et M. Ph. Millie (ENS, Paris) de nous avoir apporté des éléments de discussion constructifs.     

The influence of pentaamminerhodium(III) on the1H n.m.r. spectra and pyrrole pKas of coordinated imidazoles and pyrazoles

Summary The following [(NH₃)₅RhLH]Cl₃ salts were preparedvia the [(NH₃)₅Rh(O₃SCF₃)](O₃SCF₃)₂ synthetic route; LH=1-methylimidazole (1CH₃imH), 2-methylimidazole (2CH₃imH), 4-methylimidazole (4CH₃imH), 5-methylimidazole(5CH₃imH), and pyrazole (pyzH). pK_a's at 25.0°C were determined for [(NH₃)₅RhLH]³⁺ complexes as follows: 2CH₃imH, 10.4±0.1; 5CH₃imH/4CH₃imH isomer mixture, 10.3±0.1; pyzH, 6.54±0.05. The influence on the pK_a's of imidazoles is dominated by withdrawal of the rhodium(III) centre and may be compensated by the presence of ring methylation by only 0.5log units for cobalt(III) and rhodium(III) derivatives, compared to 1.3 units for the -withdrawing ruthenium(III) centre. In the case of the -acceptor pyrazole ring, [(NH₃)₅Rh]³⁺ is observed to serve as a slight -donor and raises the pK_a above the cobalt(III) analogue. The¹H n.m.r. spectra of [(NH₃)₅RhLH]³⁺ complexes of the substituted imidazoles and pyrazole exhibit a deshielding order. C–2H>C–5H>C–4H for imidazoles and C–3H>C–5H>C–4H for pyrazole, as do their cobalt(III) analogues. The magnitude of values (=_{free L}-_complex) are virtually the same as in the cobalt(III) systems which shows that TIP influences are unimportant compared to ring rehybridization in estabilishing chemical shifts for both the cobalt(III) and rhodium(III) complexes. The imidazolato and pyrazolato complexes exhibit resonances upfield of the respective substituted imidazole or pyrazole complex in keeping with more negative charge on the rings; the influence is largest at C–2H of imidazolates and C–3H of pyrazolate.     

Synthesis, Structure, and Reversible Thermochromism of Guanidinium Hexabromotellurate(IV)

Guanidinium hexabromotellurate(IV), C₂H₁₂N₆TeBr₆, has been synthesized and characterized by element analysis and diffuse reflectance spectroscopy. Its crystal structure has been determined (R=0.027). The complex is built from layers of [TeBr₆]^2– anions and [CH₅N₃H]⁺ cations linked by N–H...Br hydrogen bonds and united by van der Waals interactions into a 3D framework. The electronic factors governing the spectral behavior of the complexes at 100 and 300 K are discussed, and reversible thermochromism has been revealed.     

Phosphorus-containing podands 7. Complexing properties of ortho-diphenylphosphinyl-substituted diphenyl ethers of oligoethylene glycols with respect to alkali-metal cations

Stability constants of complexes of alkali-metal cations with oligoethylene glycol diethers RO(CH₂CH₂O)_nR (n=1–5), where R=2-Ph₂P(O)C₆H₄ and 2-Ph₂(O)-4-t-BuC₆H₃P, have been determined conductometrically in a tetrahydrofuran-chloroform mixture (41 by volume). The dependence of complexing ability on a number of monopodand donor centers for Li⁺ and Na⁺ has multiple extrema. For K⁺, Rb⁺, and Cs⁺ the complexing abilities steadily increase with the length of the ligand polyether chain. Monopodands based on triethylene glycol and its pyrocatechol analog are highly effective (log K=6.7–7.0) with respect to Li⁺. The synthesis of ligands with a lipophilic tert-butyl substituent in the terminal group is described.For previous communication, see [1]. The number of the communication in [2] is 5, not 4 as printed in error.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 1992–2000, September, 1991.     

D/H isotope effects in π-complexes of deuterated hexamethylbenzenes with the nitrosonium cation

The isotope effects of deuterium, manifested in the¹³C NMR spectra of complexes of deuterated hexamethylbenzenes C₆(CD₃)_n·(CH₃)_6–n with the nitrosonium cation, have been studied. The small values observed for the isotopic perturbation are evidence of -bonding of the NO⁺ group the hexamethylbenzene molecule. The applicability of an additive scheme of calculation of isotope effects for the ring carbon atoms of the complexes, based on the increments of replacement of the CH₃ group by CD₃ in hexamethylbenzene, has been demonstrated.Novosibirsk Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences, 630090 Novosibirsk. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 9, pp. 2104–2109, September, 1992.     

Mass-spectrometric investigation of coordination compounds of nickel(II) with radical anions of S-alkyl-1-phenylisothiosemicarbazides

The electron-impact mass spectra of coordination compounds of nickel(II) with the general formula NiL₂, in which the radical anions [C₆H₅N -N-C(SR)=NR¹]^–, where R=CH₃ and R=H(I), R=CD₃ and R=H(II), R=C₂H₅ and R=H(III), and R=CH₃ and R=C₆H₅(IV), serve as the ligands, have been studied. In the mass spectra of compounds I–IV the peaks of the molecular ions have the highest intensity among the organometallic fragments. The initial stage of the fragmentation of [M]^+. is associated with the formation of the rearrangement ions [NiL + H]⁺, [NiL + C₆H₅]⁺, and [NiL + SR]⁺, ions, whose appearance becomes understood, if it is taken into account that the removal of one ligand is accompanied by the impairing of spins and the mass spectra of compounds I–IV is the presence of lines for the [NiL]⁺ ion in them. The dissociative ionization of compounds I–IV is strongly reminiscent of the behavior of ordinary complexes of metals with ligands of the nonradical type. The fragmentation scheme of the molecular ions under the effects of electron impact has been presented and discussed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 3, pp. 368–371, May–June, 1990.     

Mössbauer spectroscopic studies in alkali metal hexakis (trimethylacetato) ferrate(III) complexes and their thermal decomposition products

Mössbauer spectra of hexakis (trimethylacetato) ferrate(III) complexes with general formula M₃[Fe{OCOC(CH₃)₃}₆] (where M=H⁺, Li⁺, Na⁺, K⁺ and NH ₄ ⁺ ) exhibit a quadrupole doublet with E_Q=0.31–0.65 mms^–1 and =0.60–0.74 mms^–1 (with respect to S.N.P. as standard). Infrared studies suggest unidentate coordination of the carboxylate ligands. Anomalously high and E_Q values for H₃[Fe{OCOC(CH₃)₃}₆] have been explained in terms of possible hydrogen bonding. Thermal decomposition studies show fast and single stage decomposition yielding a constant weight at 320°C. Mössbauer spectra of intermediates after heating complexes at different temperatures indicate increasing E_Q values. At 350°C, all complexes exhibit six-line spectra, suggesting the formation of alkali metal ferrate (Na₂O·NaFeO₂) or Fe₂O₃.     

Binuclear bis(β-diketonato) complexes of ruthenium(III) containing triphenylphosphine or triphenylarsine

Stable bis(-diketonato) bridged binuclear complexes prepared by reacting [RuX₃(EPh₃)₃] (X = Cl or Br; E = P or As) with (RCO)(MeCO)CH–Y–CH(COR)(COMe) [R = Me or Ph; Y = (CH₂)₆, (CH₂)₁₀] in a 2:1 molar ratio in benzene, have been characterised by elemental analyses, i.r., electronic, e.p.r. and cyclic voltammetry. The oxidation state of the metal ion in these complexes is confirmed as + 3 by electrochemical and by e.p.r. measurements. The complexes belong to a low-spin d⁵ configuration. An attempt has been made to ascertain the effect of the length of the bridging ligand on the electron transfer processes by cyclic voltammetry in these binuclear complexes. Based on the above studies an octahedral geometry has been tentatively proposed. The new complexes have been subjected to the antifungal activity studies.     

Reactions of the radial cattions of acetic acid and acetic anhydride in CFCl3

The ESR spectra of -irradiated, at –196 °C, solutions of acetic acid and acetic anhydride were studied depending on their concentrations in CFCl₃. The structure of thus produced radical cations is confirmed with the deuterium substituted analogues. It has been shown that the ion-molecular reaction of the radical cation CH₂COOH⁺ in the isolated dimer takes place for the dilute solutions of acetic acid in CFCl₃ resulting in the formation of CH₃COO follwed by its decomposition to CH₃+CO₂ while the radicals CH₂COOH are formed via secondary processes. The reactions of radical cations of acetic oxide have been also studied.     

Synthesis of an intercalated compound of montmorillonite and 6-polyamide

Natural montmorillonite, fractionated from bentonite produced in Yamagata, Japan, was ion-exchanged for NH ₃ ⁺ –(CH₂)₁₁–COOH, NH ₃ ⁺ –(CH₂)₅–COOH, Al³⁺, Cu²⁺, Mg²⁺, Co²⁺, Li⁺, K⁺ and H⁺. The mixtures of the ion-exchanged montmorillonite and -caprolactam were heated at 263°C in glass ampoules for various periods. The intercalated compounds before and after the heating were examined by X-ray powder diffraction, DSC and GPC. Although -caprolactam was not polymerized without montmorillonite, it was polymerized at 263°C in the presence of montmorillonite. The polymerization rate varied with the interlayer cations in the order of NH ₃ ⁺ –(CH₂)₁₁–COOH>Al³⁺>NH ₃ ⁺ –(CH₂)₅–COOH>H⁺>Cu²⁺>Mg²⁺>Co²⁺>Li⁺>K⁺. After heating at 263°C for 5 h, the mean number-average molecular weight was about 1.5×10⁴. Although the interlayer distance of NH ₃ ⁺ –(CH₂)₁₁–COOH type montmorillonite/-caprolactam compound increased from 2.85 nm to 4.90 nm by heating at temperatures above the melting point of -caprolactam, those of other compounds were not changed. After heating at 263°C, an intercalated compound of montmorillonite and 6-polyamide, whose interlayer distance was more than 10 nm, was obtained. It is concluded that montmorillonite acts as a Brönsted acid and initiates the open ring polymerization of -caprolactam and that the driving force of swelling is the polymerization energy.Presented at the Fourth International Symposium on Inclusion Phenomena and the Third International Symposium on Cyclodextrins, Lancaster, U.K., 20–25 July 1986.     

Ab initio calculations of small hydrides including electron correlation

Five different structures of CH₅ ⁺ and one structure of CH₅ ^– are calculated using a gaussian basis both in the SCF approximation and with the inclusion of electron correlation in the independent electron pair approximation (IEPA). While on SCF level the C _sstructure of CH₅ ⁺ has to lowest energy, the energy difference between the C _sand C _2vstructures becomes negligible if correlation is included. In contrast to this the approach of a proton to CH₄ at large and intermediate distances is most favorable towards a corner of the CH₄ tetrahedron which means a structure. The decomposition of CH₅ ⁺ into CH₃ ⁺ and H₂ requires 20kcal/mol on SCF level and 40 kcal/mol if correlation is included.     

Ruthenium(II)/(III) complexes of bidentate acetyl hydrazide Schiff bases

A series of octahedral Ru^II/Ru^III complexes of the type [Ru(Y)(CO)(BAX)(PPh₃)₂] and [RuCl₂(BAX)(PPh₃)₂] (Y = H or Cl; BAX = benzaldehydeacetylhydrazone anion; X = H, Me, OMe, OH, Cl or NO₂) have been prepared and characterised by spectral, magnetic and cyclic voltammetric studies. The Ru^II complexes are low spin diamagnetic (S = 0) whereas the Ru^III complexes are low spin and paramagnetic (S = 1/2). These Ru^II and Ru^III complexes absorb in the visible region respectively at ca. 16,000 and 28,000 cm^–1 which bands are assigned to the MLCT. The correlation of the _max values of the Ru^III complexes with the ⁺ Hammett parameter, is linear, indicating the profound effect of substituents on the electron density of the central metal. I.r. spectral data reveals that the hydrazone is chelated to ruthenium through the hydrazinic nitrogen and the deprotonated enolic oxygen. The rhombic nature of the e.s.r. spectra of the Ru^III complexes indicates an asymmetry in the electronic environment around the Ru atom. Ru^II complexes in CH₂Cl₂ show an irreversible Ru^II/III redox couple at ca. 0.9–0.5 V, while the Ru^III complexes show two reversible redox couples in the –0.1–0.1 and 0.8–0.6 V range, indicating that the higher oxidation state of ruthenium is stabilised by hydrazones.     

Synthesis,thermodynamic properties and kinetics of the acid-catalyzed dissociation of nickel(II) diamido polyamino complexes

The ligands 1,10-N,N-bis(2-hydroxymethylbenzoyl)-1,4,7,10-tetraazadecane (L₁) and 1,11-N,N-bis(2-hydroxymethylbenzoyl)-1,4,8,11-tetraazaundecane (L₂) have been synthesized. The stability constants of Ni^II complexes of ligands L₁ and L₂ have been studied at 25 °C using pH titrations. The kinetics of general acid (HCl, 0.04–2.34 mol dm^–3) or buffer (DEPP or DESPEN, 0.05 mol dm^–3, pH 4.83–5.72)-catalyzed dissociation of these Ni^II complexes have been investigated at 25 °C using a stopped-flow spectrophotometer. The ionic strength of solution was controlled at I = 2.34 mol dm^–3 (KCl + HCl) and I = 0.1 mol dm^–3 (KNO₃, buffer), respectively. The kinetic dissociation of Ni^II complexes catalyzed by HCl obeys the equilibrium k _obs = k _1d + k _2H[H⁺], whereas in buffer solution the observed rate constant k _obs = k _d + k _1H[H⁺]. At pH < 1.5, both the proton-assisted and direct protonation pathways contribute to the rates, whereas solvation is the dominant pathway at pH > 6. In the 4.8–5.7 pH range, the complexes dissociate mainly through a proton-assisted pathway.     

Disordered Crystal Structure of Bis[(2.2.2-Cryptand)Sodium] Bis[Aqua(Isothiocyanato)(μ-Isothiocyanato)Sodium] 2[Na(2.2.2-Crypt)]+ · [Na2(NCS)2(μ-NCS)2(H2O)2]2–

Crystals of bis[(2.2.2-cryptand)sodium] bis[aqua(isothiocyanato)(-isothiocyanato)sodium]: 2[Na(C₁₈H₃₆N₂O₆)]⁺ · [Na₂(NCS)₂(-NCS)₂(H₂O)₂]^2– (I) were synthesized and studied by X-ray diffraction analysis. The disordered structure of I (a = 12.715 Å, b = 10.458 Å, c = 21.767 Å, = 102.56°, space group P2₁/n) was solved by the direct method and refined by the full-matrix least-squares method in anisotropic approximation to R = 0.058 from 3896 independent reflections (CAD4 automated diffractometer, MoK ). The crystal consists of two complex ions [I¹]⁺ and [I²]^2– (molar ratio 2 : 1). The Na⁺ cation of the host–guest cation I¹ is coordinated by all eight heteroatoms (6O + 2N) of the cryptand ligand. The coordination polyhedron of this Na⁺ cation is a distorted cube. The atoms of two groups (CH₂–CH₂ and CH₂–O–CH₂–CH₂) in the cryptand ligand are disordered over two positions. The independent cation Na⁺ of the centrosymmetric binuclear complex anion I² is coordinated by one bifurcated O atom of the disordered water molecule and by three N atoms of the SCN^– ligands (including two bridging ligands). The coordination polyhedron of this Na⁺ caiotn is a distorted tetrahedron. The complex ions in the crystal structure of I are united by hydrogen bonds.     

Synthesis,Oxygenation and Catalytic Epoxidation Performance of Salen and Salophen Transition-Metal Complexes with Aza-Crown or Morpholino Pendants

Co^II and Mn^III complexes with aza-crown or morpholino substituted Salen and Salophen ligands were synthesized starting from benzo-10-aza-15-crown-5 or morpholine. The saturated oxygen uptake of the Co^II complexes CoL¹–CoL⁴ in MeOCH₂CH₂OMe solution was determined at different temperatures. The equilibrium constant (KO₂) and thermodynamic parameters (H ⁰, S ⁰) for oxygenation were calculated. Meanwhile, the corresponding Mn^III complexes, MnL¹Cl–MnL⁴Cl, were employed as models of mimic mono-oxygenase to catalyze PhCH=CH₂ epoxidation at ambient temperature and pressures. The modulation of O₂-binding capabilities and catalytic oxidation performance by these pendant substituents in the complexes were investigated and compared with the parent complexes ML⁵(Msalen) and ML⁶(Msalophen). The results indicate that the dioxygen affinities and catalytic oxidation activities of these complexes have been much more enhanced by aza-crown pendants than by morpholino pendants. Moreover, the O₂-binding capabilities of bis(aza-crown ether) Co^II complexes, CoL¹ and CoL², would also be improved by adding alkali metal (Li⁺, Na⁺ and K⁺) cations to the system. Adding K⁺ shows the most significant enhancement of dioxygen affinity through its forming sandwich-type complexes with two aza-crown ethers of CoL¹ and CoL². Likewise, the bis(aza-crown ether) Mn^III complexes, MnL¹ and MnL², exhibit the best catalytic activity: the conversions of PhCH=CH₂ attain 76.6, 79.5% respectively.     

Kinetics and mechanism of complex formation between O-bonded cis-(diglycinato)bis(ethylenediamine)cobalt(III) and α-cis-(diglycinato) (triethylenetetramine)cobalt(III) with nickel(II) in aqueous medium

Summary The kinetics of reversible complexation of Ni(OH₂) _inf6 ^sup2+ with oxygen-bonded glycinatocobalt(III) substrates N₄-Co(glyH)gly²⁺ [N₄ = (en)₂ or trien; glyH = H₃N⁺CH₂-COO^–] have been investigated by the stopped-flow technique in the 20–35° C range, at pH = 6.08–6.82 and I = 0.3 mol dm^–3. The formation of N₄Co(glyH)glyNi⁴⁺ occurred via the reaction of Ni(OH₂) _inf6 ^sup2+ with the deprotonated form of the cobalt(III) substrates, N₄Co-(glyH)gly²⁺. The rate and activation parameters for the formation and dissociation of the binuclear species are reported. The formation rate constants k _f (at 25° C), activation enthalpy and entropy H , S for N₄Co-(glyH)glyNi⁴⁺ are 320±49, 341 ± 52dm³mol^–1 s^–1, 78 ± 7, 79 ± 5 kJmol^–1 and 64 ± 24, 69 ± 18 JK^–1 mol^–1 for the ethylenediamine and triethylenetetraminecobalt(III) substrates, respectively. This result indicates that the rate and activation parameters are virtually independent of the nature of N₄ moities, which strongly suggests that the formation of mono-bonded species occurs via entry of one of the pendant NH₂ groups into the coordination sphere of nickel(II) via a rate-limiting Ni-OH₂ bond dissociation mechanism (I_d). The binuclear species exist in dynamic equilibrium between the monodentate and chelated forms, with the chelate form predominating. The low values of spontaneous dissociation rate constant for the binuclear species (k _r- 0.095^–1 at 25° C) in comparison with the high values of dissociation rate constants of monodentate nickel(II) complexes reported in the literature also support the chelate nature of the binuclear species.