Sorption of neptunyl(V) cations on suspended silicate: Effects of pH, ionic strength, complexing anions, humic acid, and metal ions

Sorption of NpO₂ ⁺ on silicate (10.00 g/l) particles dispersed in sodium perchlorate media was studied as a function of pcH and ionic strength at 298 K. The sorption increased with increased pcH in the range of ∼6.5 to 9.2, above which saturation was observed. An increase in ionic strength from 0.20M to 1.00M (NaClO₄), increased the NpO₂ ⁺ sorption, which then decreased at 1.50M (NaClO₄) for 7<pcH<8.5. The effects of different types of ligands on the sorption of NpO₂ ⁺ to suspended silicate were investigated. The types of ligands included: (i) inorganic anions (fluoride, carbonate, phosphate (ii) N-donors (ethylenediamine, 1,10 phenanthroline (iii) carboxylic acids (oxalic acid, citric acid, iminodiacetic acid, ethylenediaminetetraacetic acid) and (iv) humic acid. A synergistic enhancement in sorption to the suspended silicate was observed for phosphate, oxalate, ethylenediaminetetraacetic acid, ethylenediamine, 1,10 phenanthroline (5<pcH<8) and humic acid (6.5<pcH<8.8). This behavior was attributed to the formation of ternary NpO₂ ⁺/silicate/ligand complexes. The effects of Ca(II) (1.00·10⁻³M) and Eu(III) (1.00·10⁻⁴ and 1.00·10⁻³M) ions on NpO₂ ⁺ sorption to suspended silicate were also investigated. On leave from Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai-400 085, India.     

Sorption behavior of Am<Superscript>3+</Superscript> on suspended pyrite

Sorption behavior of ²⁴¹Am (~10⁻⁹ M) on naturally occurring mineral pyrite (particle size: ≤70 μm) has been studied under varying conditions of pH (2–11), and ionic strength (0.01–1.0 M (NaClO₄)). The effects of humic acid (2 mg/L), other complexing anions (1 × 10⁻⁴ M CO₃ ²⁻, SO₄ ²⁻, C₂O₄ ²⁻ and PO₄ ³⁻), di- and trivalent metal ions (1 × 10⁻³ M Mg²⁺, Ca²⁺ and Nd³⁺) on sorption behavior of Am³⁺ at a fixed ionic strength (I = 0.10 M (NaClO₄)) have been studied. The sorption of ²⁴¹Am on pyrite increased with pH from 2.8 (84%) to 8.1 (97%). The sorption of ²⁴¹Am decreased with ionic strength at low pH values (2 ≤ pH ≤ 4), but was insensitive in the pH range of 4–10, suggesting the formation of outer-sphere complexes on pyrite surface at lower pH, and inner-sphere complexes at higher pH values. The sorption of ²⁴¹Am increased in the presence of (i) humic acid (5 < pH < 7.5), and (ii) C₂O₄ ²⁻ (2 < pH < 3). By contrast, other complexing anions such as (carbonate, phosphate, and sulphate) showed negligible influence on ²⁴¹Am sorption. The presence of Mg²⁺, Ca²⁺ ions showed marginal effect on the sorption profile of ²⁴¹Am; while the presence of Nd³⁺ ion suppressed its sorption significantly under the conditions of present study. The sorption of ²⁴¹Am on pyrite decreased with increased temperature indicating an exothermic process.     

Silicate complexation of NpO<Subscript>2</Subscript><Superscript>+</Superscript> ion in perchlorate media

Complexation behavior of NpO₂ ⁺ with ortho-silicic acid (o-SA) has been studied using solvent extraction at ionic strengths varying from 0.10 to 1.00M (NaClO₄) at pcH 3.68±0.08 and 25 °C with bis-(2-ethylhexyl) phosphoric acid (HDEHP) as the extractant. The stability constant value (log β₁) for the 1:1 complex, NpO₂(OSi(OH)₃), was found to decrease with increase in ionic strength of the aqueous phase [6.83±0.01 at I=0.10M to 6.51±0.02 at I = 1.00M]. These values have been fitted in the SIT model expression and compared with similar values of complexation of the metal ions Am³⁺, Eu³⁺, UO₂ ²⁺, PuO₂ ²⁺, Np⁴⁺, Ni²⁺ and Co²⁺. The speciation of NpO₂ ⁺-o-silicate/carbonate system has been calculated as a function of pcH under ground water conditions. On leave from Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai-400 085, India.     

Sorption of uranyl ion on hydrous silica: Effects of ionic strength and ethylenediaminetetraacetic acid (EDTA)

The effects of ionic strength and of ethylenediamin et etraacetic acid (EDTA) on the sorption of uranyl ion, UO₂ ²⁺, to SiO₂·xH₂O (silica gel) were investigated. It was observed that pH and the ions present in the supporting electrolytes influence the ionic strength effects. The presence of different sodium salts in the concentration range (0.20 to 1.40M) suppressed the sorption of UO₂ ²⁺ in the order: NaNO₃ < NaClO₄ < NaCl < NaOCOCH₃ < Na₂SO₄ [pH 2.75(±0.05)], while the presence of perchlorate salts of Li⁺, Na⁺ and Ca²⁺ (0.20 to 1.40M) promoted the sorption of UO₂ ²⁺ on silica gel in the order: LiClO₄∼NaClO₄<Ca(ClO₄)₂ at pH 2.80(±0.05). The ionic strength effect on UO₂ ²⁺ sorption was studied in presence of EDTA (0–1.00·10⁻³M) in the pH range 2.90 to 5.57. The sorption data and speciation calculation suggest negligible complexation of UO₂ ²⁺ with EDTA at I≥1.00M NaClO₄. On leave from Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai, 400 085, India.     

Calculations of chemical equilibria in heparin-arginine-H<Subscript>2</Subscript>O-NaCl and MCl<Subscript>2</Subscript>-heparin-arginine-H<Subscript>2</Subscript>O-NaCl systems (M = Ca<Superscript>2+</Superscript>, Mg<Superscript>2+</Superscript>) in a physiological solution

Chemical equilibria in the high-molecular-weight heparin (Na₄hep)-arginine (HArg)-H₂O-NaCl and MCl₂-Na₄hep-HArg-H₂O-NaCl systems of electrolytes (M = Ca²⁺, Mg²⁺) were calculated by the method of mathematical simulation of chemical equilibria from representative planned pH-metric titration experiment at 2.30 ≤ pH ≤ 10.50 in a physiological solution medium in the presence of 0.154 M NaCl as a background electrolyte at 37°C. The initial concentrations of the basic components were n × 10⁻³ M (n ≤ 4).     

Solubility and hydrolysis of lutetium at different [Lu<Superscript>3+</Superscript>]<Subscript>initial</Subscript>

Solubility product (Lu(OH)_3(s)⇆Lu³⁺+3OH⁻) and first hydrolysis (Lu³⁺+H₂O⇆Lu(OH)²⁺+H⁺) constants were determined for an initial lutetium concentration range from 3.72·10⁻⁵ mol·dm⁻³ to 2.09·10⁻³ mol·dm⁻³. Measurements were made in 2 mol·dm⁻³ NaClO₄ ionic strength, under CO₂-free conditions and temperature was controlled at 303 K. Solubility diagrams (pLu_aq vs. pC _H) were determined by means of a radiochemical method using ¹⁷⁷Lu. The pC _H for the beginning of precipitation and solubility product constant were determined from these diagrams and both the first hydrolysis and solubility product constants were calculated by fitting the diagrams to the solubility equation. The pC _H values of precipitation increases inversely to [Lu³⁺]_initial and the values for the first hydrolysis and solubility product constants were log₁₀ β* _Lu,H = −7.92±0.07 and log₁₀ K*_sp,Lu(OH)3 = −23.37±0.14. Individual solubility values for pC _H range between the beginning of precipitation and 8.5 were S _Lu3+ = 3.5·10⁻⁷ mol·dm⁻³, S _Lu(OH)2+ = 6.2·10⁻⁷ mol·dm⁻³, and then total solubility was 9.7·10⁻⁷ mol·dm⁻³.     

Interaction of trivalent f-element cations with iodide in methanol + water solvents

The stability constants (β ₁) of iodide ion-pairs of trivalent f-block element ions (lanthanoids Ce, Eu, Gd, Tb and Tm, and actinoid Am) were determined in the vicinity of pH 2.5 of mixed methanol/water solvent solutions of an ionic strength of 1.00 mol·dm⁻³ at 298±1 K. The values were less than 2. From the variation in distance between Eu³⁺ and I⁻, which was calculated using a Born-type equation for Gibbs’ free energy derived from β ₁(Eu), the Eu³⁺-I⁻ interaction was shown to be solvent-shared ion-pair formation when the mole fraction of methanol (X _MeOH)≤0.40. In contrast, it was suggested that the interaction of Am³⁺-I⁻ changed from solvent-separated ion-pair to solvent-shared ion-pair with increasing X _MeOH when X _MeOH≤0.10, but remained as solvent-shared ion-pair in the range 0.16≤X _MeOH≤0.40. Furthermore, β ₂(Am) was measured in the range 0.31≤X _MeOH≤0.40. It was also shown that the β ₁ values of lanthanoids at X _MeOH = 0.40, except for that of Gd(III), decreased with increasing atomic number.     

Sorption behavior of Co(II) on γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> in the presence of humic acid

The fate and transport of toxic metal ions and radionuclides in the environment is generally controlled by sorption reactions. The extent of sorption of divalent metal cations is controlled by a number of factors including cosorbing or complexing. In this work, the effects of pH, humic acid HA/Co(II) addition orders, ionic strength, concentration of HA, and foreign cations on the Co(II) sorption on γ-Al₂O₃ in the presence of HA were investigated. The sorption isotherms of Co(II) on γ-Al₂O₃ in the absence and presence HA were also studied and described by using S-type sorption model. The experimental results showed that the Co(II) sorption is strongly dependent on the pH values, concentration of HA, but independent of HA/Co(II) addition orders, ionic strength, and foreign cations in the presence of HA under our experimental conditions. The results also indicated that HA enhanced the Co(II) sorption at low pH, but reduced the Co(II) sorption at high pH. It was hypothesized that the significantly positive influence of HA at low pH on the Co(II) sorption on γ-Al₂O₃ was attributed to strong surface binding of HA on γ-Al₂O₃ and subsequently the formation of ternary surface complexes such as ≡S-OOC-R-(COO⁻) _x Co^2−x . Chemi-complexation may be the main mechanism of the Co(II) sorption on γ-Al₂O₃ in the presence of HA.     

Enthalpies of formation of the complexes [Co<Superscript>2+</Superscript>-N,N-bis(carboxymethyl)aspartic acid] in aqueous solutions at 298.15 K

Enthalpies of complex formation between N,N-bis(carboxymethyl)aspartic acid (H₄Y) with Co²⁺ ion at 298.15 K are determined by calorimetry over a wide range of ionic strengths (KNO₃). Thermodynamic characteristics of the formation reactions of the complexes CoY²⁻, CoY₂⁶⁻, and Co(OH)Y³⁻ are calculated at zero and other values of ionic strength. The obtained values are interpreted.     

Application of the Specific Ion Interaction Theory → the Solubility Product and First Hydrolysis Constant of Europium

The specific ion interaction theory (SIT) was applied to the first hydrolysis constants of Eu(III) and solubility product of Eu(OH)₃ in aqueous 2, 3 and 4 mol⋅dm⁻³ NaClO₄ at 303.0 K, under CO₂-free conditions. Diagrams of pEu_aq versus pC_H were constructed from solubilities obtained by a radiometric method, the solubility product log₁₀ K_{sp, Eu(OH)3}^I {Eu(OH)_3(s) Eu_aq³⁺+ 3OH_aq⁻ } values were calculated from these diagrams and the results obtained are log₁₀ K_sp,Eu(OH)3^I = − 22.65 ± 0.29, −23.32 ± 0.33 and −23.70 ± 0.35 for ionic strengths of 2, 3 and 4 mol⋅dm⁻³ NaClO₄, respectively. First hydrolysis constants {Eu_aq³⁺+H₂O Eu(OH)_(aq)²⁺+H⁺ } were also determined in these media by pH titration and the values found are log₁₀β_Eu,H^I = − 8.19 ± 0.15, −7.90 ± 0.7 and −7.61 ± 0.01 for ionic strengths of 2, 3, and 4 mol⋅dm⁻³ NaClO₄, respectively. Total solubilities were estimated taking into account the formation of both Eu³⁺ and Eu(OH)²⁺ (7.7 < pC_H < 9) and the values found are: 1.4 × 10⁻⁶ mol⋅dm⁻³, 1.2 × 10⁻⁶ mol⋅dm⁻³ and 1.3 × 10⁻⁶ mol⋅dm⁻³, for ionic strengths of 2, 3 and 4 mol⋅dm⁻³ NaClO₄, respectively. The limiting values at zero ionic strength were extrapolated by means of the SIT from the experimental results of the present research together with some other published values. The results obtained are log₁₀ K_{sp, Eu(OH)3}^o = − 23.94 ± 0.51 (1.96 SD) and log₁₀β_Eu,H⁰ = − 7.49 ± 0.15 (1.96 SD).     

Thermodynamics of citrate complexation with Mn<Superscript>2+</Superscript>, Co<Superscript>2+</Superscript>, Ni<Superscript>2+</Superscript> and Zn<Superscript>2+</Superscript> ions

Isothermal titration calorimetry has been used to determine the stoichiometry, formation constants and thermodynamic parameters (ΔG ^o, ΔH, ΔS) for the formation of the citrate complexes with the Mn²⁺, Co²⁺, Ni²⁺ and Zn²⁺ ions. The measurements were run in Cacodylate, Pipes and Mes buffer solutions with a pH of 6, at 298.15 K. A constant ionic strength of 100 mM was maintained with NaClO₄. The influence of a metal ion on its interaction energy with the citrate ions and the stability of the resulting complexes have been discussed.     

Kinetic and thermodynamic studies of cesium(I) sorption on hydrous silica

Summary Batch sorption experiments of cesium, Cs⁺, on SiO₂ ^. xH₂O (silica gel) have been conducted with variable times of equilibration, amounts of silica gel (0.10-1.00 g), cesium concentrations (5.00 ^. 10^-5-2.40 ^. 10^-3M), ionic strengths (0.20-1.40M NaClO₄), pH (2.50-7.70), and temperatures (273-333 K). The diffusion coefficient of Cs⁺ ion was calculated to be (9.19±0.86) ^. 10^-11 m^{2 .} s^-1 under particle diffusion-controlled conditions. The sorption rate was (3.94±0.65) ^. 10^-3 s^-1 at 298 K, pH 7.70±0.05 in 0.20M NaClO₄. The sorption data fits the Freundlich, Langmuir and Dubinin-Radushkevich (D-R) isotherms. Cesium sorption on 0.20 g silica gel decreased with ionic strength from (40.42±0.34)% in 0.20M NaClO₄ to (6.35±0.40)% in 1.40M NaClO₄, at pH_(initial) 8.20±0.05. A gradual decrease in pH with increased ionic strength is consistent with a cation-exchange mechanism. Sorption of Cs⁺ on silica gel decreased with increased temperature, indicating an exothermic enthalpy. The presence of anions such as fluoride, carbonate, phosphate and oxalate in the aqueous medium did not influence the cesium sorption profile.     

Critical Evaluation of Protonation Constants. Literature Analysis and Experimental Potentiometric and Calorimetric Data for the Thermodynamics of Phthalate Protonation in Different Ionic Media

The protonation constants of phthalate were determined in aqueous NaCl (0.1 ≤ I ≤ 5,mol⋅L⁻¹) and in aqueous Me₄NCl (0.1 mol⋅L⁻¹ ≤ I ≤ 3,mol⋅L⁻¹) at t = 25,^∘C. Experimental data were employed in conjunction with literature data from studies in different ionic media (Et₄NI: 0 ≤ I ≤ 1,mol⋅L⁻¹; NaClO₄: 0.05 mol⋅L⁻¹ ≤ I ≤ 2,mol⋅L⁻¹)to study the dependence on ionic strength using different models, such as the SIT and Pitzer equations, and an Extended Debye-Hückel type equation. Experimental calorimetric data in NaCl and protonation constants at different temperatures in Et₄NI (5 ≤ t ≤ 45^∘C) and in NaClO₄ (15 ≤ t ≤ 35 ^∘C) were also used to study their dependence on temperature. Recommended equilibrium data are reported together with a short discussion of a prospective protocol for drawing these data.     

Effect of organic acids on sorption of uranyl ions in solution onto ZrP<Subscript>2</Subscript>O<Subscript>7</Subscript>

Hydration of zirconium diphosphate (ZrP₂O₇) conduced to formation of active sites in solid/liquid interface. In ZrP₂O₇/NaClO₄ 0.5 M suspensions, active sites and their acidity constants are quite determined but the presence of some impurities is now studied. This work was conducted to determine the surface properties changes produced by oxalic and citric acid during the hydration process. Moreover the presence of organic acids with ZrP₂O₇ modified reveals an increase in uranium sorption constants. The zirconium diphosphate has been characterized using X-ray powder diffraction (XRD), Scanning electron microscopy (SEM) and Particle induced X-ray emission and Neutron (PIXE). Furthermore, the specific surface area, measured by the BET method, was 3.5 m²/g. The pH corresponding to the isoelectric point, determined by Zeta Potential measurements and mass titration was 3.6. The sites density calculated using titration curves was around of 5.37 s/nm² for NaClO₄ 0.5 M_, 13.71 s/nm² for NaClO₄ 0.5 M/citric acid 0.1 M and 7.33 s/nm² NaClO₄ 0.5 M/oxalic acid 0.1 M. The surface acidity constants and species distribution in surface were calculated by means of simulation of the titration curves with the FITEQL code (constant capacitance model), for ZrO and PO amphoteric sites of ZrP₂O_7. The uranyl sorption edge was determined for NaClO₄ 0.5 M. It spreads between pH 3 and 4.5 for complete sorption according to the previously published results. In the ZrP₂O₇–citrate modified surface, the uranyl sorption edge begin at pH 2 and was almost complete at pH 3.2 while ZrP₂O₇–oxalate modified surface edge started at 50% of sorption at pH of 1.5 and was complete at pH 3.     

Investigation of radionuclide <Superscript>63</Superscript>Ni(II) sorption on ZSM-5 zeolite

The sorption of ⁶³Ni(II) from aqueous solution using ZSM-5 zeolite was investigated by batch technique under ambient conditions. ZSM-5 zeolite was characterized by point of zero net proton charge (PZNPC) titration. The sorption was investigated as a function of shaking time, pH, ionic strength, foreign ions, humic acid (HA), fulvic acid (FA) and temperature. The results indicate that the sorption of ⁶³Ni(II) on ZSM-5 zeolite is strongly dependent on pH. The sorption is dependent on ionic strength at low pH, but independent of ionic strength at high pH values. The presence of HA/FA enhances ⁶³Ni(II) sorption at low pH values, whereas reduces ⁶³Ni(II) sorption at high pH values. The sorption isotherms are simulated by Langmuir model very well. The thermodynamic parameters (i.e., ∆H ⁰, ∆S ⁰ and ∆G ⁰) for the sorption of ⁶³Ni(II) are determined from the temperature dependent sorption isotherms at 293.15, 313.15 and 333.15 K, respectively, and the results indicate that the sorption process of ⁶³Ni(II) on ZSM-5 zeolite is spontaneous and endothermic.     

Extraction chromatographic study on the separation of Am<Superscript>3+</Superscript> and Eu<Superscript>3+</Superscript> using ethyl-BTP as the extractant

Ethyl-substituted bis-triazinylpyridine (Et-BTP), a nitrogen containing soft-donor extractant, was used in investigations pertaining to the separation of Am³⁺ and Eu³⁺ from dilute nitric acid feed solutions by extraction chromatography using XAD-4 as the inert support, chlorinated dicarbollide as the modifier and 2-nitrophenyloctylether (NPOE) as the diluent. After carrying out a series of experiments, the optimum composition of the extractant mixture for the resin was found out to be 0.1 M Et-BTP and 0.025 M CCD in NPOE. Separation factor values were encouraging to carry out subsequent batch uptake studies at varying nitrate ion concentration which indicated favourable separation behaviour up to NaNO₃ concentration of 2 M. Column studies have been carried out and conditions for elution and separation of Am³⁺ from Eu³⁺ have been found out. Long term stability of the resin was also investigated.     

Complexation studies of Co<Superscript>2+</Superscript>ion with orthosilicic acid

Summary The complexation behavior of Co²⁺with ortho-silicic acid (o-SA) has been studied as a function of ionic strength (I) from 0.20 to 1.00M (NaClO₄) at pH 4.96±0.03 and 25 °C by solvent extraction with bis(2-ethylhexyl) phosphoric acid (HDEHP) as the extractant. The stoichiometry of the extracted species was determined to be Co(DEHP)₂(HDEHP)₂. Co²⁺forms a 1:1 complex, CoOSi(OH)₃⁺, as the predominant species witho-SA concentrations of 3.00^. 10^-4to 4.00^. 10^-3M. The stability constant (logb₁) values for CoOSi(OH)₃⁺complex decrease with the increase in ionic strength. These values were fitted with the extended Debye-Huckel expression to obtain the value of logb₁at I=0.00M. The effect of aging time of the o-SA solution on logb₁values for CoOSi(OH)₃⁺complex was investigated and compared with those of the UO₂OSi(OH)₃⁺complex.     

Complexes of Zr<Superscript>IV</Superscript> and Hf<Superscript>IV</Superscript> with monolacunary Keggin-and Dawson-type anions

The reactions of the tetranuclear hydroxo complexes [M₄(μ₂-OH)₈(H₂O)₁₆]⁸⁺ (M = Zr or Hf) with the lacunary Keggin-type ([α-PW₁₁O₃₉]⁷⁻) and Dawson-type ([α ₂-P₂W₁₇O₆₁]¹⁰⁻) phosphotungstates in aqueous solutions produce the sandwich polyoxometalate complexes [M(α-PW₁₁O₃₉)₂]¹⁰⁻ (M = Zr (1) or Hf (2)) and [M(α ₂-P₂W₁₇O₆₁)₂]¹⁶⁻ (M = Zr (3) and Hf (4)). The complexes were isolated and structurally characterized as salts with potassium and dimethylammonium cations. The zirconium and hafnium atoms have a square antiprismatic coordination environment (coordination number is 8). In all complexes, the mutual arrangement of the ligands corresponds to the syn isomer. Hafnium complexes 2 and 4 are the first structurally characterized polyoxometalate complexes of this metal. The structures of the resulting compounds were confirmed also by ³¹P NMR spectroscopy in solution. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 214–218, February, 2007.     

Formation of excited uranyl in oxidation of tetravalent uranium with oxygen in HClO<Subscript>4</Subscript> aqueous solutions: IV. Enhancement of the chemiluminescent reaction in the presence of Fe<Superscript>2+</Superscript>

Experimental data that support the hypothesis on the determining role of ^•OH radicals in the emergence of luminescence during the oxidation of U(IV) with atmospheric oxygen in aqueous HClO₄ solutions have been obtained using the H₂O₂-FeSO₄ system as a source of OH radicals. It has been found that brighter chemiluminescence (CL) is observed in the presence of 10⁻⁵ mol/l Fe²⁺ in a 5 × 10⁻⁴ mol/l U(IV) solution in 0.1 mol/l HClO₄ compared with the FeSO₄-free solution. The CL yield in the presence of Fe²⁺ (η_CL = 3.9 × 10⁻⁸) is 2.8 times that in the solution without iron (η_CL = 1.4 × 10⁻⁸). These results can be regarded as a further piece of evidence for the idea that the elementary event of the formation of a CL emitter—electronically excited uranyl ion *(UO₂²⁺)—in radical chain U(IV) oxidation reactions is electron transfer from the uranoyl ion (UO₂⁺) to the oxidant, the ^•OH radical. Thus, one of the main prerequisites for light emission during U(IV) oxidation reactions is a high generation efficiency of ^•OH radicals and their easy access to the uranoyl UO₂⁺ ion.     

Pivalates with the M<Superscript>II</Superscript><Subscript>4</Subscript>O<Subscript>4</Subscript> cubane core (M = Co,Ni): synthesis,structure, magnetic properties,and solid-state thermolysis

Methods were developed for the controlled thermal synthesis of high-spin cubane-like pivalates {M^II ₄(μ₃−OR)₄} (M = Co or Ni; R = H or Me) starting from mono-and polynuclear complexes. The solid-state thermal decomposition of the known pivalate clusters [M^II ₄(μ₃−OMe)₄−(μ₂−OOCBu^t)₂(η²−OOCBu^t)₂(MeOH)₄] and the new clusters [M₄^II(μ₃)−OH₄(η¹−OOCBu^t)₃−(μ−(NH₂)₂C₆H₂Me₂)₃(η¹−(NH₂)₂C₆H₂Me₂)₃]⁺(OOCBu^t)− (M = Co or Ni) was studied by differential scanning calorimetry and thermogravimetry. The thermolysis of cubane-like CoII and NiII pivalates is a destructive process. The phase composition of the decomposition products is determined by the nature of coordinated ligands and the structural features of the metal core.