Synthesis and spectral properties of titanium(iv) polynuclear hydroxo complexes stabilized in solution by the [PW11O39]7− heteropolyanion

Unsaturated heteropolyanions (HPA) [PW₁₁O₃₉]⁷⁻ stabilize Ti^IV hydroxo complexes in aqueous solutions (Ti: PW₁₁ [PW₁₁O₃₉]⁷⁻⪯12, pH 1–3). Spectral studies (optical,¹⁷O and³¹P NMR, and IR spectra) and studies by the differential dissolution method demonstrated that Ti^IV hydroxo complexes are stabilized through interactions of polynuclear Ti^IV hydroxo cations with heteropolyanions [PW₁₁TiO₄₀ ⁵⁻ formed. Depending on the reaction conditions, hydroxo cations Ti _n−1O _x H _y ^m+ either add to oxygen atoms of the W−O−Ti bridges of the heteropolyanions to form the complex [PW₁₁TiO₄₀·Ti _n−1O _x H _y ] ^k− (at [HPA]=0.01 mol L⁻¹) or interact with Ti^IV of the heteropolyanions through the terminal o atom to give the polynuclear complexes [PW₁₁O₃₉Ti−O−Ti _n−1O _x H _y ]^q− (at [HPA]=0.2 mol L⁻¹). When the complexes of the first type were treated with H₂O₂, Ti^IV ions added peroxo groups. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 914–920, May, 1997.     

Isotope effect in the formation of hydrogen peroxide by the sonolysis of light and heavy water

The kinetics of the formation of hydrogen peroxide by the sonolysis of light and heavy water in argon and oxygen atmospheres was investigated. The sonochemical reaction has a zero order with respect to hydrogen peroxide (H₂O₂, D₂O₂, or DHO₂). The measurement of the kinetic isotope effect (α), defined as the ratio of the reaction rates in H₂O and D₂O, carried out under argon gave a value of 2.2±0.3. The observed isotope effect decreases with an increase in the concentration of light water in H₂O−D₂O mixtures. No isotope effect is displayed in the oxygen atmosphere (α=1.05±0.10). The isotope effect is determined presumably by the mechanism of sonochemical decomposition of water molecules, which includes the H₂O−Ar^* and D₂O−Ar^* energy exchange (where Ar^* are argon atoms in the³P_2.0 excited state) in the nonequilibrium plasma generated by a shock wave, arising upon a cavitation collapse. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 645–649, April, 2000.     

Mechanistic Study of the Reactions of l-ascorbic Acid and Oxalic Acid with an Octahedral Manganese(IV) Complex of 1,8-bis(2-hydroxybenzamido)-3,6-diazaoctane

The Mn^IV complex of 1,8-bis(2-hydroxybenzamido)-3,6-diazaoctane (Mn^IVL) with phenolate-amido-amine coordination is reduced by l-ascorbic acid and oxalic acid obeying overall 1:1 stoichiometry. The reactions are biphasic and Mn^IIIL⁻ is the reactive intermediate. The product of oxidation of ascorbic acid (H₂Asc) is dehydroascorbic acid and that of oxalic acid (H₂OX) is CO₂, while Mn^II is the end product from Mn^IV. Both Mn^IVL and Mn^IIIL⁻ form outer sphere adducts with H₂Asc and H₂OX with high values of equilibrium constants of formation (Q>10² dm³ mol⁻¹, I = 0.5 mol dm⁻³, 25.8 °C, 1.5% v/v MeOH+H₂O). The adduct formation is diffusion controlled and is attributed to hydrogen bonding interactions between the reactants. The rate constants for the electron transfer in (Mn^IV/^IIIL, H₂A), (Mn^IV/^IIIL, HA⁻) (H₂A = H₂Asc, H₂OX) and for (Mn^IVL, H₂Asc)+H₂Asc, (Mn^IIIL⁻, HAsc⁻)+HAsc⁻ are reported. There was no evidence of direct coordination of the reductants to the Mn^IV/III center indicating an outer sphere (ET) mechanism.     

Kinetic and mechanistic studies on the electron-transfer reactions between diaquabisethylenediaminecobalt(III) and ethylenediaminetetraacetatocobaltate(III) with promazine in acidic aqueous media

The kinetics of the electron-transfer reactions between promazine (ptz) and [Co(en)₂(H₂O)₂]³⁺ in CF₃SO₃H solution ([Co^III] = (2–6) × 10⁻³ m, [ptz] = 2.5 × 10⁻⁴ m, [H⁺] = 0.02 − 0.05 m, I = 0.1 m (H⁺, K⁺, CF₃SO ₃ ⁻ ), T = 288–308 K) and [Co(edta)]⁻ in aqueous HCl ([Co^III] = (1 − 4) × 10⁻³ m, [ptz] = 1 × 10⁻⁴ m, [H⁺] = 0.1 − 0.5 m, I = 1.0 m (H⁺, Na⁺, Cl⁻), T = 313 − 333 K) were studied under the condition of excess Co^III using u.v.–vis. spectroscopy. The reactions produce a Co^II species and a stable cationic radical. A linear dependence of the pseudo-first-order rate constant (k _obs) on [Co^III] with a non-zero intercept was established for both redox processes. The rate of reaction with the [Co(en)₂(H₂O)₂]³⁺ ion was found to be independent of [H⁺]. In the case of the [Co(edta)]⁻ ion, the k _obs dependence on [H⁺] was linear and the increasing [H⁺] accelerates the rate of the outer-sphere electron-transfer reaction. The activation parameters were calculated as follows: ΔH ^≠ = 105 ± 4 kJ mol⁻¹, ΔS ^≠ = 93 ± 11 J K⁻¹mol⁻¹ for [Co(en)₂(H₂O)₂]³⁺; ΔH ^≠ = 67 ± 9 kJ mol⁻¹, ΔS ^≠ = − 54 ± 28 J K⁻¹mol⁻¹ for [Co(edta)]⁻.     

A novel kinetic-spectrophotometric method for determination of nitrites in water

A simple, selective and sensitive kinetic method for the determination of nitrite in water was developed. The method is based on the catalytic effect of nitrite on the oxidation of methylene blue (MB) with bromate in a sulfuric acid medium. During the oxidation process, absorbance of the reaction mixture decreases with the increasing time, inversely proportional to the nitrite concentration. The reaction rate was monitored spectrophotometrically at λ = 666 nm within 30 s of mixing. Linear calibration graph was obtained in the range of 0.005–0.5 μg mL⁻¹ with a relative standard deviation of 2.09 % for six measurements at 0.5 μg mL⁻¹. The detection limit was found to be 0.0015 μg mL⁻¹. The effect of different factors such as acidity, time, bromate concentration, MB concentration, ionic strength, and order of reactants additions is reported. Interference of the most common foreign ions was also investigated. The optimum experimental conditions were: 0.38 mol L⁻¹ H₂SO₄, 5 × 10.4 mol L⁻¹ KBrO₃, 1.25 × 10.5 mol L⁻¹ MB, 0.3 mol L⁻¹ sodium nitrate, and 25°C. The proposed method was conveniently applied for the determination of nitrite in spiked drinking water samples.     

Ions with a strong symmetrical H bond in the HCl−BuiOH system by IR spectroscopy data

Ion-molecular interactions in the HCl−BuⁱOH system with different compositions (from neat isobutyl alcohol to 37 mol.% HCl) were studied by Multiple Attenuated Total Reflectance (MATR) IR spectroscopy at 30 °C. Proton disolvates (Buⁱ(H)O…H…O(H)Buⁱ)⁺ with strong symmetrical H bonds are formed upon the addition of HCl to BuⁱOH. At high concentrations of HCl (C ⁰ _HCl>33 mol.%), (Cl…H…Cl)⁻ ions are formed along with (BuⁱOH)₂H⁺. The spectra of positively and negatively charged proton disolvates were compared to those of similar ions in the HCl−PrⁱOH and HCl−MeOH systems. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2496–2500, December, 1998.     

Molecularly imprinted polymer based on chemiluminescence imaging for the chiral recognition of dansyl-phenylalanine

A new molecularly imprinted polymer (MIP)–chemiluminescence (CL) imaging detection approach towards chiral recognition of dansyl-phenylalanine (Phe) is presented. The polymer microspheres were synthesized using precipitation polymerization with dansyl-l-Phe as template. Polymer microspheres were immobilized in microtiter plates (96 wells) using poly(vinyl alcohol) (PVA) as glue. The analyte was selectively adsorbed on the MIP microspheres. After washing, the bound fraction was quantified based on peroxyoxalate chemiluminescence (PO-CL) analysis. In the presence of dansyl-Phe, bis(2,4,6-trichlorophenyl)oxalate (TCPO) reacted with hydrogen peroxide (H₂O₂) to emit chemiluminescence. The signal was detected and quantified with a highly sensitive cooled charge-coupled device (CCD). Influencing factors were investigated and optimized in detail. Control experiments using capillary electrophoresis showed that there was no significant difference between the proposed method and the control method at a confidence level of 95%. The method can perform 96 independent measurements simultaneously in 30 min and the limits of detection (LODs) for dansyl-l-Phe and dansyl-d-Phe were 0.025 μmol L⁻¹ and 0.075 μmol L⁻¹ (3σ), respectively. The relative standard deviation (RSD) for 11 parallel measurements of dansyl-l-Phe (0.78 μmol L⁻¹) was 8%. The results show that MIP-based CL imaging can become a useful analytical technology for quick chiral recognition.     

Hydrogen bond CH…O in a methanolic solution of hydrogen chloride

The existence of a hydrogen bond in which a methyl group of the (MeOH)₂H⁺ ion acts as a proton donor is examined. The fundamental vibration frequencies of this ion were calculated for different numbers and strengths of CH…O bonds. The atomic charges in neutral ((MeOH) _n ,n=1–4) and protonated ((MeOH) _m H⁺,m=2–6) associates of methanol molecules were also calculated. The experimentally observed decrease in the v(CH) vibration frequencies of the (MeOH)₂H⁺ ion to 2890 cm⁻¹ and 2760 cm⁻¹ is attributable to the fact that each methyl group of the ion is involved in formation of two CH…O bonds with strength of −12.5 kJ mol⁻¹. The proton-donating ability of the CH bond depends on the charge on its H atom; however, it does not correlate with the dipole moment of this bond. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 306–312, February, 1999.     

Determination of p-nitroaniline by the tartrate-acetone-Mn2+-KBrO3-H2SO4 double organic substrate oscillating system using non-equilibrium stationary state

This paper described the determination of p-nitroaniline in a double organic substrate oscillating system of tartrate-acetone-Mn²⁺-KBrO₃-H₂SO₄. Under the optimum conditions, temperature was chosen as a control parameter to design the bifurcation point and proposed a convenient method for determination of p-nitroaniline. Results showed that the system consisting of 3.5 mL 0.06 mol L⁻¹ tartrate, 4.0 mL 0.7 mol L⁻¹ H₂SO₄, 1.5 mL 1.5×10⁻⁴ mol L⁻¹ MnSO₄, 4.0 mL 0.4 mol L⁻¹ acetone and 7.0 mL 0.05 mol L⁻¹ KBrO₃ was very sensitive to the surrounding at 33.5°C. A good linear relationship between the potential difference and the negative logarithm concentration of p-nitroaniline was obtained to be in the range of 2.50×10⁻⁷∼3.75×10⁻⁵ mol L⁻¹ with a lower detection limit of 2.50×10⁻⁸ mol L⁻¹.      

Kinetic-potentiometric assay of formaldehyde in pharmaceutical and industrial samples, monitored by copper solid ion selective electrode, after its reaction with the copper(II)-bis-(ethylenediamine) complex

A kinetic-potentiometric method is described for the quantitative assay of formaldehyde (HCHO) in pharmaceutical and industrial preparations. It is based on the reaction of HCHO with (ethylenediamine)-Cu(II)-sulfate [Cu(CH₂NH₂)₂(H₂O)₂] · SO₄. The changes in potential, resulting from the release of the Cu(II) cations, are monitored with a Cu(II)-ion selective electrode. The calibration curve for the HCHO is linear in the concentration range 50–250 mg L⁻¹, with a limit of detection of 8.5 mg L⁻¹. The method shows very good reproducibility with an RSD of 2.6% for successive injections (n = 5) of 150 mg L⁻¹ HCHO primary solution, while it is interference free. The method was successfully tested in various industrial and pharmaceutical preparations.     

Effect of Ionic Strength and Temperature on the Protonation of Oxidized Glutathione

The protonation constants for oxidized glutathione, H _i−1L^(4−i+1)−, K _i ^H=[H _i L⁽⁴⁻ⁱ⁾⁻]/[H _i−1L^(4−i+1)−][H⁺] i=1,2,…,6 have been measured at 5, 25 and 45 °C as a function of the ionic strength (0.1 to 5.4 mol⋅[kg(H₂O)]⁻¹) in NaCl solutions. The effect of ionic strength on the measured protonation constants has been used to determine the thermodynamic values (K _i ^H0) and the enthalpy (ΔH _i ) for the dissociation reaction using the SIT model and Pitzer equations. The SIT (ε) and Pitzer parameters (β ⁽⁰⁾, β ⁽¹⁾ and C) for the dissociation products (L⁴⁻, HL³⁻, H₂L²⁻, H₃L⁻, H₄L, H₅L⁺, H₆L²⁺) have been determined as a function of temperature. These results can be used to examine the effect of ionic strength and temperature on glutathione in aqueous solutions with NaCl as the major component (body fluids, seawater and brines).     

Synthesis and characterization of new metal(II) complexes with formates and some nitrogen donor ligands

New mixed-ligands complexes with empirical formulae: M(2,4′-bpy)₂L₂·H₂O (M(II)Zn, Cd), Zn(2-bpy)₃L₂·4H₂O, Cd(2-bpy)₂L₂·3H₂O, M(phen)L₂·2H₂O (where M(II)=Mn, Ni, Zn, Cd; 2,4′-bpy=2,4′-bipyridine, 2-bpy=2,2′-bipyridine, phen=1,10-phenanthroline, L=HCOO⁻) were prepared in pure solid state. They were characterized by chemical, thermal and X-ray powder diffraction analysis, IR spectroscopy, molar conductance in MeOH, DMF and DMSO. Examinations of OCO⁻ absorption bands suggest versatile coordination behaviour of obtained complexes. The 2,4′-bpy acts as monodentate ligand; 2-bpy and phen as chelating ligands. Thermal studies were performed in static air atmosphere. When the temperature raised the dehydration processes started. The final decomposition products, namely MO (Ni, Zn, Cd) and Mn₃O₄, were identified by X-ray diffraction.     

Manganese(III)-carboxylate binding: Chemistry and structure of a hydrated pyridinedicarboxylate

The reaction of Mn(CH₃COO)₃ 2H₂O with the carboxyl-rich ligand pyridine-2,6-dicarboxylic acid (H₂L) in methanol affords a high-spin (S = 2) hydratedbis-complex. Structure determination has revealed the solid to be [Mn^III(H₂ L)(L)] [Mn^IIIL₂] 5H₂ O: space group P−1;Z = 2;a = 7.527(3)?³,b= 14.260(4)?,c = 16.080(6)?,α = 91.08(3)°,β = 103.58(3)°,γ= 105.41(3)° andV= 1611.2(10)?³. Each ligand is planar and is bonded in the tridentate O₂N fashion. The MnO₄N₂ coordination spheres show large distortions from octahedral symmetry. The lattice is stabilised by an extensive network of O…O hydrogen-bonding involving water molecules and carboxyl functions. Upon dissolution in water, protic redistribution occurs and the complex acts as the mono-basic acid Mn(HL)(L) (pK, 4.3 ±0.05). The deprotonated complex displays high metal reduction potentials: Mn^IVL₂-Mn^IIIL ₂ ⁻ , 1.05V; Mn^IIIL ₂ ⁻ Mn^IIL ₂ ²⁻ -, 0.28V vs. SCE     

A thermochemical study of the coordination reactions of La(III) with alanine and glycine

The solid-state coordination reactions of lanthanum chloride with alanine and glycine, and lanthanum nitrate with alanine have been studied by classical solution calorimetry. The molar dissolution enthalpies of the reactants and the products in 2 mol L^-1 HCl solvent of these three solid-solid coordination reactions have been measured using an isoperibol calorimeter. From the results and other auxiliary quantities, the standard molar formation enthalpies have been determined to be Δ_f H _m ^θ[La(Ala)₃Cl₃·3H₂O(s), 298.2 K]= -3716.3 kJ mol^-1, Δ_f H _m ^θ [La(Gly)₃Cl₃·5H₂O(s), 298.2 K]= -4223.0 kJ mol^-1 and Δ_f H _m ^θ [La(Ala)₄(NO₃)₃·H₂O(s), 298.2 K]= -3867.57 kJ mol^-1, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermochemical properties of trialkylarsenites

The heats of the reaction of sodium with ethyl and methyl alcohol were determined by calorimetry. The difference in the standard heats of the formation of triethylarsenite and arsenic trichloride was obtained by calorimetration of the reaction of arsenic trichloride with sodium ethylate, the value of which was −382.42 ± 3.60 kJ/mol. The standard enthalpies of formation were determined from a critical analysis of all data on thermochemistry of trialkylarsenites for the following compounds: triethylarsenite Δ_f H ₂₉₈^ℴ [(C₂H₅O)₃As(liquid)] = (−704.38 ± 3.85) kJ/mol; trimethylarsenite Δ_f H ₂₉₈^ℴ [(CH₃O)₃As(liquid)] = (−599.36 ± 1.88) kJ/mol. The values of standard enthalpies of formation were not adjusted for the following substances in liquid state: arsenic trichloride (−321.96 ± 3.85 kJ/mol), tris-(diethylamido)arsenic(III) As(NEt₂)₃(liquid) (−129.81 ± 4.41 kJ/mol), tri-n-propylarsenite (−720.61 ± 4.49 kJ/mol), triisopropylarsenite (−756.11 ± 4.65 kJ/mol), tri-n-butylarsenite (−775.11 ± 4.53 kJ/mol), and triisobutylarsenite (−809.71 ± 4.59 kJ/mol). The use of sodium alcoxide solutions for the calorimetration of halogen anhydrides of various acids was demonstrated.     

Quantum chemical study of C—H bond activation in methane molecule by AuIII aqua chloride complexes

The mechanism of the reactions of methane with the gold(III) complexes [AuCl_x(H₂O)_{4− x} ]^3−x (x = 2, 3, or 4) was studied by the DFT/PBE method with the SBK basis set. High activation barriers obtained for the reactions of [AuCl₄]⁻ and [Au(H₂O)Cl₃] with methane suggest these reactions cannot proceed under mild conditions. The reaction of the [Au(H₂O)₂Cl₂]⁺ complex with methane has a rather low energy barrier and proceeds through the formation of an intermediate complex. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 191–201, February, 2006.     

Supramolecular cobalt(II) complexes: syntheses,crystal structures and solvent effects

Two Co^II complexes, namely {[CoL(MeOH)(μ-OAc)]₂Co}·2MeCN·2MeOH (1) and {[CoL(EtOH)(μ-OAc)]₂Co}·3EtOH (2) (H₂L=3,3′-dimethoxy-2,2′-[(1,3-propylene)dioxybis(nitrilomethylidyne)]diphenol), have been synthesized and characterized by X-ray crystallography. Both complexes contain octahedral coordination geometries, comprising three Co^II atoms, two deprotonated bisoxime L²⁻ units in which four μ-phenoxo oxygen atoms form two [CoL(X)] (X = MeOH or EtOH) units, two acetate ligands coordinated to three Co^II centers through Co–O–C–O–Co bridges, and coordinated and non-coordinated solvent. Both complexes exhibit 2D supramolecular networks through different intermolecular hydrogen-bonding interactions.     

Kinetics and mechanism of interaction of hexaaquachromium(III) with <Emphasis Type="SmallCaps">l</Emphasis>-Dopa in aqueous medium: comparative antiparkinsonian studies

The kinetics and mechanism of the substitution reaction between [Cr(H₂O)₆]³⁺ and l-Dopa in aqueous medium has been studied over the range 1.8 ≤ pH ≤ 2.6, 1.68 × 10⁻² mol dm⁻³ ≤ [Dopa] ≤ 5.04 × 10⁻² mol dm⁻³, I = 0.1 mol dm⁻³ (KNO₃) at 50 °C. The reaction takes place via an outer sphere association between Cr³⁺ and l-Dopa followed by chelation. The product was characterized by physicochemical and infrared spectroscopic methods. The antiparkinsonian activity of the product was found to be higher than that of l-Dopa.     

Oxidation of the thiosulfate ion by some iron(III) complexes with phenolate - amide-amine coordination: A comparative kinetic study

The redox reactions of thiosulfate with four iron(III) complexes having phenolate-amide-amine coordination, Fe^III(L){L = 1,2-bis(2-hydroxybenzamido)ethane, L¹; 1,3-bis(2-hydroxybenzamido)propane, L²; 1,5-bis(2-hydroxybenzamido)3-azapentane, L³; and 1,8-bis(2-hydroxybenzamido)3,6-diazaoctane, L⁴} have been investigated in 10% v/v MeOH + H₂O and I = 0.3 mol dm⁻³. At constant pH (~ 4.8) and under pseudo-first order conditions of [S₂O ₃ ²⁻ ] the reaction obeyed the rate law : − d[Fe^III(L)]/dt = k _obs [Fe^III(L)] + k _obs ^′ where k _obs ^′ denotes the observed rate constant of thiosulfate decomposition; k _obs = a[S₂O ₃ ²⁻ ] + b[S₂O ₃ ²⁻ ] _T ² is valid for all the complexes, particularly at pH < 6, while k _obs ^′ = [H⁺][S₂O ₃ ²⁻ ] _T ² is consistent with the rate law for thiosulfate decomposition proposed earlier. The rate data (k _obs) were analysed on the basis of the reactivities of various species of Fe^III(L) generated by the equilibrium protonation of the sec-NH of dien and trien spacer units resulting in the ring opening (for [Fe^III(L³/L⁴)]), and acid base equilibrium of the aqua ligand bound to the iron(III) centre ([Fe^III(L)(OH₂) _n ]). The redox activities, both for second and third order paths, show the ligand dependencies : L⁴<L³<L¹<L² conforming to the fact that the complexes tend to be less susceptible to electron transfer from S₂O ₃ ²⁻ with (i) the increase of the number of chelate rings, (ii) the decrease of overall charge, and (iii) the decrease of ring size offered by the amine moiety (from six membered to five membered one as for [Fe^III(L¹/L²)(OH₂)₂]⁺. There was no evidence for the formation of inner sphere thiosulfato complex, the possibility of the formation of the outer sphere ion-pairs, [Fe(L/HL)(OH₂)n ^+/2+, S₂O ₃ ²⁻ ] with low equilibrium constant value may not be excluded. In view of this, the outer sphere electron transfer (ET) mechanism is the most likely possibility.     

Kinetic studies on chromium-glycinato complexes in acidic and alkaline media

Two solid complexes, fac–[Cr(gly)₃] and [Cr(gly)₂(OH)]₂, (where gly is glycinato ligand) were prepared and their acid-catalysed aquation products were identified. The structure of [Cr(gly)₃] was solved by X-ray diffraction, revealing a cationic 3D sublattice with perchlorate anions inside its cavities. Acid-catalysed aquation of [Cr(gly)₃] and [Cr(gly)₂(OH)]₂ leads to the same inert product, [Cr(gly)₂(H₂O)₂]⁺, in a two-stages process. At the first stage, intermediate complexes, [Cr(gly)₂(O–glyH)(H₂O)]⁺ and [Cr(gly)₂(H₂O)–OH–Cr(gly)₂(H₂O)]⁺, are formed respectively. Kinetics of the first aquation stage of [Cr(gly)₃] were studied in HClO₄ solutions. The dependencies of the pseudo first-order rate constants on [H⁺] are as follows: k _obs1H = k ₀ + k ₁ K _p1[H⁺], where k ₀ and k ₁ are rate constants for the chelate-ring opening via spontaneous and acid-catalysed reaction paths, respectively, and K _p1 is the protonation constant. The proposed mechanism assumes formation of the reactive intermediate as a result of proton addition to the coordinated carboxylate group of the didentate ligand. Some kinetic studies on the second reaction stage, the one-end bonded glycine liberation, were also done. The obtained results were analogous to those for stage I. In this case, the proposed reactive species are intermediates, protonated at the carboxylate group of the monodentate glycine. Base hydrolysis of two complexes, [Cr(gly)₂(O–gly)(OH)]⁻ and [Cr(gly)₂(OH)₂]⁻, was studied in 0.2–1.0 M NaOH. The pseudo first-order rate constants, k _obsOH, were [OH⁻] independent in the case of [Cr(gly)₂(O–gly)(OH)]⁻, whereas those for [Cr(gly)₂(OH)₂]⁻ linearly depended on [OH⁻]. The reaction mechanisms were proposed, where the OH⁻ -catalysed reaction path was rationalized in terms of formation of the reactive conjugate base, [Cr(gly)₂(OH)(O)]²⁻, as a result of OH⁻ ligand deprotonation. Activation parameters were determined and discussed.