芳基四硫富瓦烯与碘电荷转移复合物的合成及其晶体结构

采用缓慢挥发溶剂的方法合成了硫原子桥联芳基取代四硫富瓦烯（Ar-S-TTF）与碘的3种电荷转移复合物（1^+·）（I₃）·I₂、（2^+·）（I₅）·I₂和（3²⁺）（I₃）₂,采用单晶X射线衍射、紫外可见光谱、循环伏安对其进行了表征。复合物（1^+·）（I₃）·I₂为C2/c空间群,1^+·呈椅式构型。化合物1与碘之间在溶液中和复合物中电荷转移一致。复合物（2^+·）（I₅）·I₂为P1空间群,2^+·呈椅式构型。复合物（3²⁺）（I₃）₂为Pbca空间群,3²⁺呈独特的平面构型。化合物2和3与碘之间在溶液中和复合物中呈现不同的电荷转移。复合物中聚碘阴离子呈现不同的堆积结构：由I₃^-或I₅^-/I₂组成的一维链状和I₃^-/I₂组成的二维网格状。     

Bismuth compounds [Ph3BuP]+I?, [Ph3BuP] 2+ [Bi2I8 · 2Me2C=O]2?, and [Ph3BuP] 2+ [Bi2I8 · 2Me2S=O]2?: Syntheses and crystal structures

The complexes [Ph₃BuP]₂⁺[Bi₂I₈ · 2Me₂C=O]²⁻ (II) and [Ph₃BuP]₂⁺[Bi₂I₈ · 2Me₂S=O]²⁻ (III) are synthesized by the reactions of triphenyl(n-butyl)phosphonium iodide (I) with bismuth iodide in acetone and dimethyl sulfoxide. In the cations of complexes I–III, the P atoms have a distorted tetrahedral coordination (CPC angles 106.3(2)°–112.0(3)°). The butyl group in cation I is disordered over two positions. In the binuclear centrosymmetric anions of structures II and III, the octahedrally coordinated bismuth atoms are linked in pairs by two bridging (br) iodine atoms (Bi-I_br 3.1508(7) and 3.2824(8) ? in compound II, 3.1961(3) and 3.3108(3) ? in complex III), which are coplanar to four terminal (t) iodine atoms (Bi-I_t 2.9260(7) and 2.9953(6) ? in complex II, 2.9206(3) and 2.9786(3) ? in complex III). The two remaining positions at the bismuth atom are occupied by the iodine atom (Bi-I_t 2.8531(7) ? in complex II, 2.8984(3) ? in complex III) and O atom of the organic molecule (Bi-O 2.747(6) ? in complex II, 2.507(3) ? in complex III). Original Russian Text ? V.V. Sharutin, I.V. Egorova, N.N. Klepikov, E.A. Boyarkina, O.K. Sharutina, 2009, published in Koordinatsionnaya Khimiya, 2009, Vol. 35, No. 3, pp. 188–192.     

芳基四硫富瓦烯与碘电荷转移复合物的合成及其晶体结构

采用缓慢挥发溶剂的方法合成了硫原子桥联芳基取代四硫富瓦烯(Ar-S-TTF)与碘的3种电荷转移复合物(1^+·)(I₃)·I₂、(2^+·)(I₅)·I₂和(3²⁺)(I₃)₂,采用单晶X射线衍射、紫外可见光谱、循环伏安对其进行了表征。复合物(1^+·)(I₃)·I₂为C2/c空间群,1^+·呈椅式构型。化合物1与碘之间在溶液中和复合物中电荷转移一致。复合物(2^+·)(I₅)·I₂为P1空间群,2^+·呈椅式构型。复合物(3²⁺)(I₃)₂为Pbca空间群,3²⁺呈独特的平面构型。化合物2和3与碘之间在溶液中和复合物中呈现不同的电荷转移。复合物中聚碘阴离子呈现不同的堆积结构：由I₃^-或I₅^-/I₂组成的一维链状和I₃^-/I₂组成的二维网格状。     

Kinetics and mechanism of the iodine oxidation of hydroxylamine

Studies of the stoichiometry and kinetics of the reaction between hydroxylamine and iodine, previously studied in media below pH 3, have been extended to pH 5.5. The stoichiometry over the pH range 3.4–5.5 is 2NH₂OH + 2I₂ = N₂O + 4I^? + H₂O + 4H⁺. Since the reaction is first-order in [I₂] + [I₃^?], the specific rate law, k₀, is k₀ = (k₁ + k₂/[H⁺]) {[NH₃OH⁺]₀/(1 + K_p[H⁺])} {1/(1 + K_I[I^?])}, where [NH₃OH⁺]₀ is total initial hydroxylamine concentration, and k₁, k₂, K_p, and K_I are (6.5 ± 0.6) × 10⁵ M^?1 s^?1, (5.0 ± 0.5) s^?1, 1 × 10⁶ M^?1, and 725 M^?1, respectively. A mechanism taking into account unprotonated hydroxylamine (NH₂OH) and molecular iodine (I₂) as reactive species, with intermediates NH₂OI₂^?, HNO, NH₂O, and I₂^?, is proposed.     

Isolierte I102−‐Ringe,ein neues Strukturelement in der Polyiodid‐Chemie

The novel compound bis(1,4,7,10‐tetraoxa­cyclo­do­decane)­cadmium(II) decaiodide, [Cd(C₈H₁₆O₄)₂]I₁₀, contains the [Cd(12‐crown‐4)₂]²⁺ complex cation, triiodide ions and iodine mol­ecules. Two triiodide ions and two iodine mol­ecules form isolated twisted I₁₀^2? rings. The geometry of the complex cation is as expected, e.g.d(Cd—O) = 2.366 (4) and 2.394 (4) Å.     

From an Icosahedron to a Plane: Flattening Dodecaiodo‐dodecaborate by Successive Stripping of Iodine

It has been shown by electrospray ionization–ion‐trap mass spectrometry that B₁₂I₁₂^2? converts to an intact B₁₂ cluster as a result of successive stripping of single iodine radicals or ions. Herein, the structure and stability of all intermediate B₁₂I_n^? species (n=11 to 1) determined by means of first‐principles calculations are reported. The initial predominant loss of an iodine radical occurs most probably via the triplet state of B₁₂I₁₂^2?, and the reaction path for loss of an iodide ion from the singlet state crosses that from the triplet state. Experimentally, the boron clusters resulting from B₁₂I₁₂^2? through loss of either iodide or iodine occur at the same excitation energy in the ion trap. It is shown that the icosahedral B₁₂ unit commonly observed in dodecaborate compounds is destabilized while losing iodine. The boron framework opens to nonicosahedral structures with five to seven iodine atoms left. The temperature of the ions has a considerable influence on the relative stability near the opening of the clusters. The most stable structures with five to seven iodine atoms are neither planar nor icosahedral.     

Kinetics of oxidation of phenylhydrazine by a μ-oxo diiron(III,III) complex in acidic aqueous media

Phenylhydrazine (R) quantitatively reduces [Fe₂(μ-O)(phen)₄(H₂O)₂]⁴⁺ (1) (phen?=?1,10-phenanthroline) and its conjugate base [Fe₂(μ-O)(phen)₄(H₂O)(OH)]³⁺ (2) to [Fe(phen)₃]²⁺ in presence of excess 1,10-phenanthroline in the pH range 4.12–5.55. Oxidation products of phenylhydrazine are dinitrogen and phenol. The reaction proceeds through two parallel paths: 1?+?R?→?products (k ₁), 2?+?R?→?products (k ₂); neither RH⁺ nor the doubly deprotonated conjugate base of the oxidant, [Fe₂(μ-O)(phen)₄(OH)₂]²⁺ (3) is kinetically reactive though both are present in the reaction media. At 25.0°C, I?=?1.0?M (NaNO₃), the rate constants are k ₁?=?425?±?10?M^?1?s^?1 and k ₂?=?103?±?5?M^?1?s^?1. An inner-sphere, one-electron, rate-limiting step is proposed.     

Heterometallic iodoplumbates modified by copper(I) or silver(I) with viologens

Cu/Ag(I) were introduced into iodoplumbate systems to produce two new heterometallic iodoplumbates with viologen as templates, i.e. (PV)₂(Pb₂Cu₂I₁₀) (1) and [(BV)(Pb₂AgI₇)]_n (2) (PV²⁺ = propyl viologen, BV²⁺ = benzyl viologen), in which the common connection of PbI₆ units have been remarkably altered. In (PV)₂(Pb₂Cu₂I₁₀) (1), two PbI₆ octahedra are bridged by two CuI₄ tetrahedra via face-sharing to give a (Pb₂Cu₂I₁₀)^4? cluster, but the ternary one-dimensional polymeric (Pb₂AgI₇)_n^2n? of [(BV)(Pb₂AgI₇)]_n (2) is assembled from edge-sharing AgI₄ tetrahedra and PbI₆ octahedra. Their optical band gaps and fluorescence were also discussed. The absorption edges of haloplumbates could be engineered by introduction of suitable conjugated molecules as templates.     

Crystal Structure of an Unusual Hydrated Complex of 1,4,7,10,13-Pentaoxacyclohexadecane-14,16-Dione with Calcium Thiocyanate

An unusual hydrated complex of 1,4,7,10,13-pentaoxacyclohexadecane-14,16-dione (L) with calcium thiocyanate, C₂₆H₄₈Ca₂N₄O₂₀S₄ (I), was synthesized and studied by X-ray diffraction analysis (CAD4 automated diffractometer, MoK radiation). The unit cell parameters are as follows: a = 31.293 Å, b = 9.756 Å, c = 14.253 Å, space group Pca2₁, Z = 4. Structure I was solved by the direct method and refined by the full-matrix least-squares method in the anisotropic approximation (final R = 0.075 for all 5187 measured independent reflections). In crystal form, complex I is composed of oppositely charged complex ions [CaL₂(H₂O)₄]²⁺ (I ₁) and [Ca(NCS)₄(H₂O)₂]^2– (I ₂) united by an infinite three-dimensional net of hydrogen bonds. The coordination polyhedron of Ca²⁺ in ion I ₁ (CN = 7) is a distorted octahedron with a bifurcate vertex. This Ca²⁺ cation is not located in the cavities of either of the crown ligands L and is not coordinated by any of the ether O atoms. The coordination polyhedron of Ca²⁺ in ion I ₂ (CN = 6) is a distorted octahedron with two cis-arranged water molecules. This Ca²⁺ cation is also coordinated by the nitrogen atoms of four SCN^– anions.     

Reaction of excited iodine atoms with methyl iodide: Rate constant determinations

The rate constant for the reaction I(²P_1/2) + CH₃I → I₂ + CH₃ has been reevaluated taking into account both collisional deactivation of excited iodine atoms and loss of I₂ by I₂ + CH₃ → I + CH₃I. The reevaluation is based upon data obtained (R. T. Meyer), J. Chem. Phys., 46 , 4146 (1967) from the flash photolysis of CH₃I using time-resolved mass spectrometry to measure the rate of I₂ formation. Computer simulations of the complete kinetic system and a closed-form solution of a simplified set of the differential equations yielded a value of 6(± 4) × 10⁶ 1./mole-sec for the excited iodine atom reaction in the temperature region of 316 to 447 K. A slight temperature dependence was observed, but an activation energy could not be evaluated quantitatively due to the small temperature range studied. An upper limit for the collisional deactivation of I(²P_1/2) with CH₃I was also determined (2.4 × 10⁷ 1./mole-sec).     

A Dual Plating Battery with the Iodine/[ZnIx(OH2)4−x]2−x Cathode

Plating battery electrodes typically deliver higher specific capacity values than insertion or conversion electrodes because the ion charge carriers represent the sole electrode active mass, and a host electrode is unnecessary. However, reversible plating electrodes are rare for electronically insulating nonmetals. Now, a highly reversible iodine plating cathode is presented that operates on the redox couples of I₂/[ZnI_x(OH₂)_4?x]^2?x in a water‐in‐salt electrolyte. The iodine plating cathode with the theoretical capacity of 211 mAh g^?1 plates on carbon fiber paper as the current collector, delivering a large areal capacity of 4 mAh cm^?2. Tunable femtosecond stimulated Raman spectroscopy coupled with DFT calculations elucidate a series of [ZnI_x(OH₂)_4?x]^2?x superhalide ions serving as iodide vehicles in the electrolyte, which eliminates most free iodide ions, thus preventing the consequent dissolution of the cathode‐plated iodine as triiodides.     

Synthesis and structure of bismuth complex [n-Bu4N] 2+ [Bi2I8 · 2 Me2S=O]2?

Bismuth complex [Bu₄N]₂⁺[Bi₂I₈ · 2Me₂S=O]²⁻(I) was synthesized by reacting tetrabutylammonium iodide with bismuth iodide. In the cations, an N atom has a distorted tetrahedral coordination (CNC angles change in the range from 107.9(5)° to 111.9(5)°). In the centrosymmetric binuclear anion, octahedral bismuth atoms are bound to each other through the bridging (br) iodine atoms (Bi-I_br, 3.2779(7) ? and 3.3156(9) ?), which are coplanar with four terminal (t) iodine atoms (Bi-I_t, 2.9392(7) ? and 2.9534(8) ?). Two remaining positions near the bismuth atom are occupied by an iodine atom (Bi-I, 3.0079(8) dimethyl sulfoxide (DMSO) molecule (Bi-O, 2.456(5) ?).     

Crystal and molecular structure of tetraaquabarium Di-μ-tartrato-di-μ-hydroxodigermanate(IV) pentahydrate [Ba(H2O)4][Ge2(μ-Tart)2(μ-OH)2] · 5H2O

A new heteronuclear germanium barium complex with D-tartaric acid [Ba(H₂O)₄][Ge₂(μ-Tart)₂(μ-OH)₂]·5H₂O (I) (H₄Tart is tartaric acid) was synthesized. The identity of compound I and its com- position were determined by elemental analysis and X-ray diffraction. The thermal stability of the compound was studied; the coordination centers of the ligand were found from IR spectroscopy. The structure of I was determined by X-ray crystallography. Crystals I are tetragonal: a = 8.5033(2) ?, c = 30.9393(11) ?, V = 2237.10(11) ?³, Z = 4, space group P4₁, R1 = 0.0301 based on 4215 reflections with I > 2σ(I). In crystals I, neutral [Ge₂(μ-Tart)₂] dimers are linked in pairs by double hydroxyl bridges to form {[Ge₂(μ-Tart)₂(μ-OH)₂]²⁻}_∞ polymeric chains. Hydrated Ba²⁺ cations and crystal water molecules are in between the anionic chains. Polymeric complex anions, hydrated barium cations, and H₂O molecules are bound by a system of hydrogen bonds to form a framework.     

Equilibrium,kinetics, and mechanism of the malonic acid–iodine reaction

The equilibrium constant for the reaction CH₂(COOH)₂ + I₃^? ? CHI(COOH)₂ + 2I^? + H⁺, measured spectrophotometrically at 25°C and ionic strength 1.00M (NaClO₄), is (2.79 ± 0.48) × 10^?4M². Stopped-flow kinetic measurements at 25°C and ionic strength 1.00M with [H⁺] = (2.09-95.0) × 10^?3M and [I^?] = (1.23-26.1) × 10^?3M indicate that the rate of the forward reaction is given by (k₁[I₂] + k₃[I₃^?]) [HOOCCH₂COO^?] + (k₂[I₂] + k₄[I₃^?]) [CH(COOH)₂] + k₅[H⁺] [I₃^?] [CH₂(COOH)₂]. The values of the rate constants k₁-k₅ are (1.21 ± 0.31) × 10², (2.41 ± 0.15) × 10¹, (1.16 ± 0.33) × 10¹, (8.7 ± 4.5) × 10^?1M^?1·sec^?1, and (3.20 ± 0.56) × 10¹M^?2·sec^?1, respectively. The rate of enolization of malonic acid, measured by the bromine scavenging technique, is given by k_en[CH₂(COOH)₂], with k_en = 2.0 × 10^?3 + 1.0 × 10^?2 [CH₂(COOH)₂]. An intramolecular mechanism, featuring a six-member cyclic transition state, is postulated to account for the results on the enolization of malonic acid. The reactions of the enol, enolate ion, and protonated enol with iodine and/or triodide ion are proposed to account for the various rate terms.     

New π ligand N,N,N,N′,N′,N′-hexaallylethylenediaminium (L2+): Synthesis and crystal structures of LBr2 · 2H2O and its cuprocomplexes L[CuII(Br0.45Cl3.55)], L[Cu 4I (Br4.55Cl1.45)], and L[Cu 4I Br6]

The alkylation of ethylenediamine with allyl bromide in the presence of a fourfold (with respect to ethylenediamine) molar amount of NaHCO₃ in acetone with an ethanol admixture (15: 1) affords LBr₂ · 2H₂O (I), where L²⁺ is the N,N,N,N′,N′,N′-hexaallylethylenediaminium cation. Single crystals of complexes L[Cu^II(Br_0.45Cl_3.55)] (II), L[Cu₄^I(Br_4.55Cl_1.45)] (III), and L[Cu₄^IBr₆] (IV) are prepared by ac electrochemical synthesis from an ethanolic solution of LBr₂ · 2H₂O, CuCl₂ · 2H₂O (or CuBr₂) at copper wire electrodes. The crystal structures of compounds I–IV are determined by X-ray diffraction analysis. The crystals of complex I are monoclinic: space group P2₁/n, a = 8.544(3), b = 10.404(3), c = 13.350(4) ?, β = 97.29(3)°, V = 1177.2(6) ?³, Z = 2. The bromine anions in compound I are bonded to the L²⁺ cations and water molecules through hydrogen contacts (E)H…Br (E = O, C) of 2.57(3)–2.86(3) ?. The crystals of compounds II–IV are triclinic: space group P . For II: a = 8.762(4), b = 9.163(4), c = 16.500(6) ?, α = 95.62(4)°, β = 96.39(4)°, γ = 111.46(4)°, V = 1211.4(9) ?³, Z = 2; for III: a = 9.074(4), b = 9.435(4), c = 9.829(5) ?, α = 116.12(4)°, β = 104.14(4)°, γ = 100.22(4)°, V = 692.3(6) ?³, Z = 1; for IV isostructural III: a = 9.084(4), b = 9.404(4), c = 9.869(4) ?, α = 116.31(3)°, β = 104.00(3)°, γ = 100.37(3)°, V = 692.1(5) ?³, Z = 1. Unlike the isolated tetrahedral CuX₄²⁻ anion in structure II, an original chain anion (Cu₄X₆²⁻) _n is observed in the structures of π complexes III and IV. Original Russian Text ? M.M. Monchak, A.V. Pavlyuk, V.V. Kinzhibalo, M.G. Mys’kiv, 2009, published in Koordinatsionnaya Khimiya, 2009, Vol. 35, No. 6, pp. 414–419.     

Inorganic reactions of iodine(+1) in acidic solutions

We present a thorough analysis of the former works concerning the hydrolysis of iodine and its mechanism in acidic or neutral solutions and recommend values of equilibrium and kinetic constants. Since the literature value for the reaction H₂OI⁺ ? HOI + H⁺ appeared questionable, we have measured it by titration of acidic iodine solutions with AgNO₃. Our new value, K(H₂OI⁺ ? HOI + H⁺) ～ 2 M at 25°C, is much larger than accepted before. It decreases slowly with the temperature. We have also measured the rate of the reaction 3HOI → IO₃^? + 2I^? + 3H⁺ in perchloric acid solutions from 5 × 10^?2 M to 0.5 M. It is a second order reaction with a rate constant nearly independent on the acidity. Its value is 25 M^?1 s^?1 at 25°C and decreases slightly when the temperature increases, indicating that the disproportionation mechanism is more complicated than believed before. An analysis of the studies of this disproportionation in acidic and slightly basic solutions strongly supports the importance of a dimeric intermediate 2HOI ? I₂O·H₂O in the mechanism. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36:480–493, 2004     

Zum chemischen Transport von SiAs mit Iod — Experimente und Modellrechnungen

On the Chemical Transport of SiAs using Iodine — Experiments and Thermochemical Calculations Using iodine as transport agent siliconarsenide migrates in a temperature gradient. The direction of the migration depends on the chosen temperature and the concentration of the transport agent. The transport rates were measured for various transport agent concentrations (0.0002 ? C(I₂) ≥ 0,02 mmol/cm³) and for various mean transport temperatures (650 ? T? ? 1 000°C). For low temperatures (e.g. T₁ = 750°C→T₂ = 850°C), low iodine concentrations (e.g. C(I₂) = 0.001 mmol/cm³) and in the presence of H₂O (from wall of silica ampoule) the following exothermic reaction is responsible for the deposition of SiAs-crystals in the sink region:

• SiAs_s + 4HI_g = SiI_4,g + 2H_2,g + 1/4As_4,g

In case of higher temperatures (e.g. T₂ = 1 050°C→T₁ = 950°C) and higher iodine concentrations (e.g. C(I₂) = 0.02 mmol/cm³) SiI_4,g is the transport agent. According to model calculations the following endothermic reaction is responsible for the migration of SiAs to the region of the lower temperature:

• SiAs_s + SiI_4,g = 2SiI_2,g + 1/4As_4,g

The heterogeneous and homogenous equilibria will be discussed and an explanation of the non equilibrium transport behaviour of SiAs is given. Thermochemical data of SiAs are characterized by the quartzmembrane zero manometer technique and further verified by model calculations.     

Twinned and Disordered Crystal Structure of Solvated Bis[Aqua(2.2.2-Cryptand)Calcium] Hexa(Isothiocyanato)Calcium

Twinned and disordered crystals of solvated bis[aqua(2.2.2-cryptand)calcium] hexa(isothiocyanato)calcium 2[Ca(2.2.2-Crypt)(H₂O)]²⁺ · [Ca(NCS)₆]^4– · Sol (I), where Sol is acetone and/or ethanol and may be water, were synthesized and studied by X-ray diffraction analysis. Structure I (space group P2₁/n, a = 11.841 Å, b = 21.787 Å, c = 12.377 Å, = 90.90°) was solved by the direct method and refined by the full-matrix least squares method in anisotropic approximation to R = 0.079 from 4168 independent reflections (CAD4 automated diffractometer, MoK ). In crystal form, complex I exists as the two aforesaid complex ions [I¹]²⁺ and [I²]^4– in the molar ratio 2 : 1 united through hydrogen bonds. Complex cation I¹ is of the guest–host type. Its Ca²⁺ cation is coordinated by all eight heteroatoms (6O + 2N) of the cryptand ligand and by the O atom of the water molecule; the coordination polyhedron of this Ca²⁺ cation (CN 9) is irregular. The Ca²⁺ cation of complex anion I² (in the crystallographic center of inversion) is coordinated by six N atoms of six neighboring SCN^– anionic ligands; the coordination polyhedron of this Ca²⁺ cation (CN 6) is a slightly distorted octahedron.     

Synthesis, crystal and molecular structure of tetraaquabis(nicotinamide)cobalt(II) phthalate dihydrate

The coordination compound of cobalt(II) with nicotinamide [CoL₂(H₂O)₄][C₆H₄(COO)₂] · 2H₂O (I) (where L stands for nicotinamide) was synthesized and characterized by IR spectroscopy, conductometry, and thermogravimetry. The X-ray structure of complex I was determined. Crystals are monoclinic: a = 15.630(2) ?, b = 7.550(2) ?, c = 21.035(4) ?, β = 100.90(5)°, V = 2437.4(4) ?³, Z = 4, space group C2/c. The structural units of complex I are centrosymmetrical cations [CoL₂(H₂O)₄]²⁺, anions [C₆H₄(COO)₂]²⁻ (lying on axis 2), and molecules of waster of crystallization. Complex cations are packed into layers are alternate with layers containing anions and free H₂O molecules. This is a classical case of π-π-staking interactions that lead to the formation of supramolecular layered assemblies. Original Russian Text ? A.S. Antsyshkina, G.G. Sadikov, T.V. Koksharova, I.S. Gritsenko, V.S. Sergienko, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 8, pp. 1379–1384.     

Kinetic study of the iodine-catalyzed alcoholysis of Butoxytriethylsilane: n-butoxy group—s-butoxy group exchange reaction

In order to appreciate the excellent catalytic effect of iodine on the alcoholyses of alkoxysilanes more precisely, the rates of the reaction, Et₃SiOBuⁿ + Bu^sOH ? Et₃SiOBu^s + BuⁿOH, were determined at various iodine concentrations. Both forward and reverse reactions are first order with respect to butoxysilane and to butanol, and pseudo first-order rate constants were measured at 40°, 30°, and 20°C on reaction mixtures containing both butanols in excess by means of gas-liquid chromatography. The observed rate constants as a function of iodine concentration gave linear relationships, and from these data the catalytic coefficients of iodine were evaluated: The enthalpies and the entropies of activation were estimated to be 53.2 kJ mol^?1, ?103 J K^?1 mol^?1 (forward, 30°C) and 51.8 kJ mol^?1, minus;100 J K^?1 mol^?1 (reverse, 30°C).