scispace - formally typeset
Search or ask a question

Showing papers in "Transition Metal Chemistry in 1987"


Journal ArticleDOI

174 citations


Journal ArticleDOI
TL;DR: In this paper, transfer chemical potentials have been derived from appropriate solubility measurements for several iron(II)-and iron(III)-diimine-cyanide complexes into aqueous methanol.
Abstract: The solvatochromic behaviour of several complexes [Fe(LL)2(CN)2] with LL=Schiff base diimine has been established in a series of non-aqueous solvents, as has that of two analogues containing diazabutadiene ligands. Transfer chemical potentials have been derived from appropriate solubility measurements for several iron(II)-and iron(III)-diimine-cyanide complexes into aqueous methanol, and for [Fe(bipy)2(CN)2] into several binary aqueous solvent series. The usefulness of solvatochromic shifts and transfer chemical potentials as indicators of selective solvation is discussed. Kinetics of oxidation of catechol and of 4-t-butyl catechol by [Fe(bipy)(CN)4]− in aqueous solution are described.

41 citations


Journal ArticleDOI
TL;DR: In this paper, carboxy-substituted ferrocene compounds are prepared and investigated by cyclic voltammetry in acetonitrile solution, and the half-wave potentials of most of the acids studied (E1/2=0.58 V versus s.c.
Abstract: Several carboxy-substituted ferrocene compounds are prepared and investigated by cyclic voltammetry in acetonitrile solution. The half-wave potentials of most of the acids studied (E 1/2=0.34−0.58 V versus s.c.e.) are more positive than that of ferrocene (0.33 V), reflecting a diminished susceptibility to oxidation of these compounds relative to the parent metallocene. Only β-ferrocenylpropionic acid (0.325 V) is effectively identical with the latter in its oxidation behaviour, and γ-ferrocenylbutyric acid (0.31 V) tends to be more readily oxidized. The results are of interest for subsequent chemical oxidation studies of ferrocenylcarboxylic acids.

40 citations


Journal ArticleDOI
TL;DR: A series of metal ion complexes of the thiosemicarbazone,N-methyl-2[1-(2-pyridinyl)ethylidene]-hydrazinecarbothioamide (HL4M) has been prepared and spectrally characterized as discussed by the authors.
Abstract: A series of metal ion complexes of the thiosemicarbazone,N-methyl-2[1-(2-pyridinyl)ethylidene]-hydrazinecarbothioamide (HL4M) has been prepared and spectrally characterized HL4M coordinates either as a neutral bidentate ligand (ie, pyridyl N and imine N) or as deprotonated tridentate ligand (ie, pyridyl N, imine N and thiol sulphur) The cobalt(II) salts yield hexacoordinated cobalt(III) cations, and an isoelectronic species, [Ni(L4M)2], has been formed from Ni(C2H3O2)2 The remaining nickel(II) complexes involve the neutral ligand, as do two of the three copper(II) complexes HL4M possesses a weaker ligand field and has less covalency in its bonding than related thiosemicarbazones that possess anN-dialkyl-function

31 citations


Journal ArticleDOI
TL;DR: In this paper, the ease of dimerisation of the mononuclear complexes [MI2(CO)3(NCMe)L] is discussed in terms of the electronic and steric effects of the ligands.
Abstract: The complexes [MI2(CO)3(NCMe)2] (M=Mo or W) react with one molar equivalent of L in CH2Cl2 at room temperature initially to afford the mononuclear sevencoordinate complexes [MI2(CO)3(NCMe)L] which have been isolated for L-PPh3, AsPh3, SbPh3, PPh2Cy or P(OPh3)3. Many of these complexes dimerise to give the iodide bridged compounds [{M(μ−I)I(CO)3L}2]via displacement of acetonitrile. When L=PPhCy2, PCy3, PEt3 or P(OMe)3 only the dimeric complexes have been isolated. The ease of dimerisation of the mononuclear complexes [MI2(CO)3(NCMe)L] is discussed in terms of the electronic and steric effects of the ligands, L. Low temperature13C n.m.r. spectroscopy of the mononuclear [Wl2(CO)3(NCMe)(EPh3)](E=P or As) complexes are interpreted as suggesting the likely stereochemistry of these seven-coordinate complexes.

30 citations


Journal ArticleDOI
TL;DR: In this article, the solvent, pressure, and temperature dependence of the lowest energy metal-to-ligand charge-transfer absorption bands are reported for a series of [Mo(CO)4(LL)], compounds where LL is a bidentate diimine ligand containing the chelating fragment −N=CRCR=N−.
Abstract: The solvent, pressure, and temperature-dependence of the lowest energy metal-to-ligand charge-transfer absorption bands are reported for a series of [Mo(CO)4(LL)], compounds where LL is a bidentate diimine ligand containing the chelating fragment −N=CRCR=N−, and one terdentate ligand analogue [Mo(CO)3(LLL)] The effects of ligand nature on these dependences are discussed, as are their interrelations and their connection with solvent properties such as polarity

27 citations


Journal ArticleDOI
TL;DR: In this article, rate constants for 4-cyanopyridine substitution in aqueous methanol (40 vol % MeOH) and in toluene solution at 298.2 K (ambient pressure) were investigated.
Abstract: Rate constants are reported for reaction of the 4-cyanopyridine complexes [Fe(CN)5(4CNpy)]3− and [Mo(CO)5(4CNpy)] with a variety of incoming ligands, in aqueous methanol (40 vol % MeOH) and in toluene respectively, at 298.2 K (ambient pressure). The dependence of rate constants on the nature and concentration of the incoming ligand is discussed in terms of the operation of the limiting dissociative,D, mechanism for substitution; the operation of this mechanism here, and in analogous pentacyanoferrate(II), pentacarbonylmolybdenum(I), and penta- and tetra-cyanocobaltate(III) complexes is reviewed. The effect of pressure on rate constants for replacement of 4-cyanopyridine in [Mo(CO)5(4CNpy)], in toluene solution at 298.2 K, indicates an activation volume of +3 cm3 mol−1.

26 citations


Journal ArticleDOI
TL;DR: In this article, magnetic studies and lig-and field parameters suggest a tetragonal structure for [CrCl3L] and [CrCL3L2] adducts, where L =semicarbazones or thiosemicarazones of furfuraldehyde and indole-3-carboxaldehyde.
Abstract: [CrCl3(thf)3] (thf=tetrahydrofuran) reacts with semicarbazones and thiosemicarbazones to yield adducts of the type, [CrCl3L] and [CrCl3L2] (where L=semicarbazones or thiosemicarbazones of furfuraldehyde and indole-3-carboxaldehyde). I.r. data suggest that L bind via the azomethine nitrogen and oxygen/sulphur. Magnetic studies and lig-and field parameters suggest a tetragonal structure for these complexes.

25 citations



Journal ArticleDOI
TL;DR: In this paper, a dioxouranium (VI) complex with the dibasic tridentate 7-carboxaldehyde-8-hydroxyquinoline-aroylhydrazone derivatives was synthesized and is bonded to the axial oxygen of the uranyl moiety and is easily substituted by dimethylsulphoxide.
Abstract: New dioxouranium(VI) complexes with the dibasic tridentate 7-carboxaldehyde-8-hydroxyquinoline-aroylhydrazone derivatives (1), have synthesized and is bonded to the axial oxygen of the uranyl moiety and is easily substituted by dimethylsulphoxide. The ligands contain intramolecular hydrogen bonds, one of which is from the enolic form of the hydrazone residue. The1H n.m.r. spectra show that the position of the hydrogenbonded proton of the hydrazone moiety is substituent dependent. The F(U−O) (mydn/A) and the bond length r(U−O) (A) of the UO bond are calculated from the i.r. data and related to the electronic properties of the substituents.

18 citations


Journal ArticleDOI
TL;DR: In this article, the preparation and characterization of salts of the [ReO2(CN)4]3−, ReO(NCS)(CN) 4]2−, this article 4−, [O(OH)(CN 4]4]-2− and [Re2O3(CN 8]4− species are described.
Abstract: The preparation and characterization of salts of the [ReO2(CN)4]3−, [ReO(OH)(CN)4]2−, [ReO(H2O)(CN)4]−, [Re2O3(CN)8]4− and [ReO(NCS)(CN)4]2− species are described. The nature of the protonation reactions of [ReO2(CN)4]3− was established by the successful isolation of these salts.

Journal ArticleDOI
TL;DR: In this paper, the reduction potentials of two series of complexes having the formula [M{HB(3,5-Me2C3N2H)3}(NO)Cl(NHC6H4Z-p)], in which M=Mo and Z=F, Cl, Br, OMe, SMe, CN, CO2Me or NO2, have been prepared.
Abstract: Two series of complexes having the formula [M{HB(3,5-Me2C3N2H)3}(NO)Cl(NHC6H4Z-p)]; in which M=Mo and Z=F, Cl, Br, OMe, SMe, CN, CO2Me or NO2 and M=W and Z=Br, OMe, CN, CO2Me or NO2, have been prepared. The reduction potentials of these new complexes were measured by cyclic voltammetry and, in combination with previously reported data for related species and for [Mo{HB(3,5-Me2C3N2H)3} (NO)I-(NHC6H4Z-p], were used to determine reaction constants for the reduction of [M{HB(3,5-Me2C3N2H)3}(NO)X(NHC6H4Z)]M=Mo and X=I or Cl; M=W, X=Cl.

Journal ArticleDOI
TL;DR: In this article, the synthesis and characterization of 2-acetylpyridine-semicarbazone (apsc) and aptsc and their complexes with CoCl2, CrCl3 and CuCl2 are reported.
Abstract: The synthesis and characterization of 2-acetylpyridine-semicarbazone (apsc) and 2-acetylpyridinethiosemicarbazone (aptsc) and their complexes with CoCl2, CrCl3 and CuCl2 are reported. These compounds were characterized on the basis of elemental analyses, electronic and i.r. spectra, magnetic moments and conductivity measurements. The molar conductivities in dimethyl formamide indicate the non-ionic nature of the metal chelates. An octahedral structure is proposed for the chromium(III) chelate-complexes, tetrahedral for the copper(II) compounds and tetrahedral or octahedral for the cobalt(II). Apsc and aptsc are bidentate but with different donors, though aptsc is monodentate in its complex with CrCl3.

Journal ArticleDOI
TL;DR: In this paper, the spectral and thermal properties of Benzenesulphonylhydrazine (HB) complexes have been characterized by spectral (uv, ir, nmr), magnetic and thermal (dta, dtg, tg, dsc) measurements.
Abstract: Benzenesulphonylhydrazine (HB) reacts with bivalent metal ions either in the keto-or enol forms The complexes have been characterized by spectral (uv, ir, nmr,), magnetic and thermal (dta, dtg, tg, dsc) measurements Ir spectra suggest that HB is monodentate coordinatingvia NH or NH2, depending on the medium of the reaction The participation of the O=S=O group in bondingvia bridge-formation in a polymeric chain is also considered The substitution of ethanol in the CoII complex, [(CoB2EtOH)n], by H2O, pyridine or acetonitrile was also investigated

Journal ArticleDOI
TL;DR: In this article, an octahedral geometry has been established for all the ruthenium(III) complexes except [Ru(L″)Cl2]n, which is pentacoordinate and a trigonal-bipyramidal environment, D3h, has been suggested for the RIT ion.
Abstract: Ruthenium(III) complexes of types [Ru(L)3], [Ru(L′)Cl(H2O)2], [Ru(L″)Cl2]n, [Ru(L‴)Cl(H2O)]n(LH =Schiff bases derived from anthranilic acid and benzaldehyde, acetophenone, vanillin, cinnamaldehyde orm-hydroxyacetophenone; L′H2=Schiff bases derived from anthranilic acid and salicylaldehyde oro-hydroxyacetophenone; L″H=Schiff bases derived fromp-aminobenzoic acid and benzaldehyde, acetophenone, vanillin, cinnamaldehyde orm-hydroxyacetophenone; L‴H2=Schiff bases derived fromp-aminobenzoic acid and salicylaldehyde oro-hydroxyacetophenone) have been synthesized and characterized on the basis of elemental analyses, conductance, magnetic moment and spectral (electronic, i.r. and1H n.m.r.) data. The wavelengths of the principal electronic absorption peaks have been accounted for quantitatively in terms of crystal field theory and various parameters have been evaluated. On the basis of the electronic spectra, an octahedral geometry has been established for all these complexes except [Ru(L″)Cl2]n. The complexes [Ru(L″)Cl2]n are pentacoordinate and a trigonal-bipyramidal environment, D3h, is suggested for the ruthenium(III) ion. The thermal behaviour of these complexes has also been studied by t.g., d.t.g and d.s.c techniques. Heats of reaction for the decomposition steps were calculated from the d.s.c. curves. The antifungal and antiviral activities of the complexes with Schiff bases derived from anthranilic acid were also investigated.

Journal ArticleDOI
TL;DR: Reaction of Lawessons reagent withbis-phosphine-dihalide complexes of nickel, palladium and platinum proceeds with asymmetric bridge cleavage to give new compounds, characterised by31P n.m.r. and microanalyses.
Abstract: Reaction of Lawessons reagent (MeOC6H4P(S)S2P(S)C6H4OMe) (1) withbis-phosphine-dihalide complexes of nickel, palladium and platinum proceeds with asymmetric bridge cleavage to give M(PR3)2(S2(S)PC6H4OMe) (2). The new compounds were characterised by31P n.m.r., i.r. and microanalyses.

Journal ArticleDOI
TL;DR: In this paper, a mixed ligand complex of palladium(II) containing diethylenetriamine as a primary ligand and amino acids as secondary ligands was made by the pH titration method at 25° C and ionic strengthM=0.1.
Abstract: Equilibrium studies of mixed ligand complexes of palladium(II) containing diethylenetriamine as a primary ligand and amino acids as secondary ligands were made by the pH titration method at 25° C and ionic strengthM=0.1. Different equilibrium constants, characteristic of binary and mixed ligand complexes were calculated and the chelation mode was deduced from conductivity measurements.

Journal ArticleDOI
TL;DR: The 95Mo n.m.r. spectra for a series of molybdenum(0) complexes [Mo(CO)5L] (L=N,P,As, or Sb donor ligands) have been observed; resonances occur in the −1433 to −1864 ppm range for the twenty-six complexes with the 95Mo shielding order being: N
Abstract: The95Mo n.m.r. spectra for a series of molybdenum(0) complexes [Mo(CO)5L] (L=N,P,As, or Sb donor ligands) have been observed; resonances occur in the −1433 to −1864 ppm range for the twenty-six complexes with the95Mo shielding order being: N

Journal ArticleDOI
TL;DR: In this article, the empirical composition of 2-hydroxy-1-naphthaldehyde oxaldihydrazone (HNODH) and HNMDH has been characterized by elemental analysis, magnetic susceptibility, electronic and i.r.
Abstract: Polymeric complexes prepared by solid-solution reactions, from 2-hydroxy-1-naphthaldehyde oxaldihydrazone (HNODH) and 2-hydroxy-1-naphthaldehyde malondihydrazone (HNMDH), had the empirical composition M(L-2H)·nH2O where M=FeII, MnII, CoII, NiII, CuII, ZnII, CdII and HgII; L=HNODH, HNMDH andn=0,1, 2. The complexes, which are intensely coloured and insoluble in common organic solvents, were characterized by elemental analysis, magnetic susceptibility, electronic and i.r. spectral data. The absence of anions indicates that the ligands which bind the metal ions from the hydroxyl and the imino groups have been deprotonated.

Journal ArticleDOI
TL;DR: In this paper, the half-field absorption in the ΔMs=±2 region of the X-band e.p.r. spectra has been observed for the dimeric and polymeric copper(II) complexes.
Abstract: Dimeric and polymeric copper(II) complexes containing BPCA (N-2-pyridinylcarbonyl-2-pyridinecarboximidate), having general formulae Cu(BPCA)X·nH2O (X=Cl, Br, NCS, NCO, N3, or CN) and Cu2(BPCA)2-X·nH2O [X=oxalate anion (OX), chloranilate anion (CA) or the dianion of 2,5-dihydroxy-1,4-benzoquinone (DHBQ)] have been synthesized by the copper(II)-assisted hydrolysis of 2, 4, 6-tris(2-pyridyl)-1, 3, 5-triazine. Spectroscopic results indicate five-coordinate, approximately square-pyramidal, geometry around the copper(II) ion. Half-field absorption in the ΔMs=±2 region of the X-band e.p.r. powder spectra has been observed for the dimeric species.

Journal ArticleDOI
TL;DR: The structure of [S(CH2CH2)3S]2[Re2O3(CN)8]·4H2O has been determined from three-dimensional x-ray diffraction data.
Abstract: The structure of [S(CH2CH2)3S]2[Re2O3(CN)8]·4H2O has been determined from three-dimensional x-ray diffraction data. The blue crystals are monoclinic, space group P21/c, with cell dimensionsa=9.431(2),b=10.879(2),c=16.217(3)A, β=110.84(2)°,Z=2 andD m=2.11 gcm−3. Anisotropic refinement by least-squares methods of 2483 observed reflections converged toR=0.050. The centrosymmetric binuclear anion has a linear O=Re−O−Re=O grouping with an eclipsed configuration for the cyano ligands. Bond distances: Re−O (terminal)=1.69(1), Re−O (bridging)=1.921(1) and Re−Cav=2.12(2)A. Each Re atom is displaced by 0.11(2)A towards the terminal oxygen atom giving a slight square-pyramidal distortion of the octahedral environment. The ring-constrained cation has C−Sav=1.82(2)A with averaged bond angles C−S−C=101(1) and S−C−C=113(1)°.

Journal ArticleDOI
TL;DR: In this article, a series of spin-paired hexa-coordinated mixed-ligand cyanonitrosyl complexes of chromium (with {CrNO}5 electron configuration(1)) of the type [Cr(NO)(CN) 2(L)2(H2O)] (where L=4-methyl-2-pyrazoline-5-one(1), 2,3-dimethyl-1-phenyl-3-polymethyl-polymorphine-5,one(2) or 4-dimethylamino
Abstract: A new series of spin-paired hexa-coordinated mixed-ligand cyanonitrosyl complexes of chromium (having {CrNO}5 electron configuration(1)) of the type [Cr(NO)(CN)2(L)2(H2O)] (where L=4-methyl-2-pyrazoline-5-one(1), 2,3-dimethyl-1-phenyl-3-pyrazoline-5-one(2) or 4-dimethylamino-2,3-dimethyl-1-phenyl-3-pyrazoline-5-one(3) have been synthesized in the solid state by the interaction of potassium pentacyanonitrosylchromate(I) monohydrate, K3[Cr(NO)(CN)5]· H2O with L in aqueous acetic acid. The products, which have been characterized by elemental analyses, molar conductances, thermogravimetric analyses, magnetic measurements, electron spin resonance and infrared spectral studies, contain low-spin chromium(I). An octahedral structure has been suggested for the complexes.

Journal ArticleDOI
TL;DR: In this article, the binding sites of the bidentate bridging L− and the unidentate terminal LH are discussed, and the possible binding sites for the unidentified terminal LH and the single monoanionic L− ligands bridging between adjacent Pd2+ or Pt4+ ions.
Abstract: Complexes of the general types Pd(L)(LH)Cl (LH=hxH, xnH, or tbH) and Pt(L)(LH)Cl3 (LH=hxH, or xnH) are formed by boiling under reflux 2∶1 molar mixtures of hypoxanthine (hxH), xanthine (xnH) or theobromine (tbH) and PdCl2 or PtCl4 in ethanol-triethyl orthoformate. These complexes appear to be linear chain polymeric species, characterized by single monoanionic L− ligands bridging between adjacent Pd2+ or Pt4+ ions. Inclusion of one terminal neutral LH and one terminal chloro-ligand completes the coordination sphere in the square-planar Pd2+ complexes, while the Pt4+ complexes aretrans-octahedral, involving three terminal chloro and one terminal LH ligand per platinum. The possible binding sites of the bidentate bridging L− and the unidentate terminal LH are discussed.

Journal ArticleDOI
TL;DR: In this paper, a synthesis of [RhH{P(OPh)3}4] (1) from [Rh(acac){P[OPh]3}2] or [Rh[acac)(CO)2] has been developed.
Abstract: A synthesis of [RhH{P(OPh)3}4] (1) from [Rh(acac){P(OPh)3}2] or [Rh(acac)(CO)2] has been developed. The reaction of theortho-metallated complex (2) with H2, leading to (1) is described.

Journal ArticleDOI
TL;DR: In this article, the synthesis and characterization of 4-acetyl-pyridinesemicarbazone (4-apsc) and its complexes with CrCl3, CoCl2 and CuCl2 are reported.
Abstract: The synthesis and characterization of 4-acetyl-pyridinesemicarbazone (4-apsc) and 4-acetylpyridine-thiosemicarbazone (4-aptsc) and their complexes with CrCl3, CoCl2 and CuCl2 are reported. These compounds were characterized on the basis of elemental analyses, electronic and i.r. spectra, magnetic moments and conductivities measurements. The compounds are nonconductors in dimethylformamide. Tentative structures for the complexes are suggested.

Journal ArticleDOI
TL;DR: In this paper, the mixed-ligand complexes of palladium(II) containing diethylenetriamine as a primary ligand and α-amino acid esters as secondary ligands were studied using potentiometric and conductometric techniques.
Abstract: The mixed-ligand complexes of palladium(II) containing diethylenetriamine as a primary ligand and α-amino acid esters as secondary ligands were studied using potentiometric and conductometric techniques. The equilibrium and/or stability constants of the binary and mixed-ligand complexes formed were determined. The kinetics of base hydrolysis of the above esters in the presence and absence of PdII-dien complexes were studied at 30°C. The rate and catalysis constants were determined.

Journal ArticleDOI
TL;DR: In this article, a tervalent nickel ion in a tetragonal geometry with four donor groups from the oxime ligand in the equatorial plane and two axially bound water molecules is described.
Abstract: The preparation of new stable tervalent nickel complexes of syn-2-picolylphenyl- and syn-2-picolylmethyl-ketoxime, PPKOH and PMKOH, respectively, are reported. Complexes of the general formula, [NiL2(H2O)2]X (L=PPKO or PMKO and X=Cl or Br) have been isolated and are soluble in water and in most organic solvents. E.s.r. spectra are consistent with a tervalent nickel ion in a tetragonal geometry with four donor groups from the oxime ligand in the equatorial plane and two axially bound water molecules. The unpaired electron is located in an orbital which has a large amount ofdz2 character. The ease of formation and the stability of nickel(III) relative to nickel(II) is proved by the electrode potential versus the standard hydrogen electrode of 0.69 V. Two nickel(III) complexes form on reaction with pyridine, in which pyridine replaces first one and then the second axially bound water molecule.

Journal ArticleDOI
TL;DR: In this paper, the synthesis and structural features of some biologically active benzothiazolines derived by the condensation of various aldehydes and ketones such as pyridine 2-aldehyde, furfuraldehyde, thiophene-2-aldehyde and terpthaldehyde with 2-aminothiophenol are described.
Abstract: This paper describes the synthesis and structural features of iron(II) complexes of some biologically active benzothiazolines derived by the condensation of various aldehydes and ketones such as pyridine 2-aldehyde, furfuraldehyde, thiophene-2-aldehyde, indole-3-carboxaldehyde, benzil, biacetyl, glyoxal, and terpthaldehyde with 2-aminothiophenol. An attempt has been made to characterize the resulting complexes by elemental analysis, conductance measurement, molecular weight determination and electronic, infrared,1H and13C n.m.r. spectral studies. An octahedral geometry has been suggested on the basis of magnetic measurements and Mossbauer spectra.

Journal ArticleDOI
TL;DR: In this paper, the authors studied the kinetics of the catalytic decomposition of hydrogen peroxide in the presence of Dowex-50W resin in the form of some transition metal-ion ammine complexes in an aqueous medium.
Abstract: The kinetics of the catalytic decomposition of hydrogen peroxide was studied in the presence of Dowex-50W resin in the form of some transition metal-ion ammine complexes in an aqueous medium. The transition metal-ions, Co2+, Ag+, Cd2+ and Zn2+ were chosen in this study and the rate constants (per gram of dry resin) were evaluated at various resin weights in the 25–40°C range. A coloured compound (peroxo-metal complex), which formed at the beginning of the reaction in each case, was found to contain the catalytic active species. Probable mechanisms for the reactions are proposed. The activation energy and the change in the entropy of activation increased in the following sequence: [Ag(NH3]2]+< [Cd(NH3)6]2+<[Co(NH3)6]2+<[Zn(NH3)6]2+, which is also the probability sequence for the formation of the activated complex.

Journal ArticleDOI
TL;DR: In this article, the effect of temperature on the solvolysis of trans-[Co(4-Etpy)4Cl2]- (1) (EtPy=ethylpyridine) was investigated in water and in a wide range of water+methanol mixtures.
Abstract: The solvolysis of trans-[Co(4-Etpy)4Cl2]+ (1) (Etpy=ethylpyridine) was investigated in water and in a wide range of water+methanol mixtures. The effect of temperature on the solvolysis was considered and the thermodynamic parameters of activation were calculated. The free energies of transfer of (1) in the initial state were calculated from the solubility of the complex [Co(4-Etpy)4Cl2]2[ReCl6]. The free energy of transfer of the cation (1) in the transition state was calculated using a free energy cycle. The effect of the solvent structure on (1) is dominant in the transition state, where −ΔGto(1) transition >−ΔGto(1) initial. Comparison of the present thermodynamic data with those obtained previously fortrans-[Co(4-Mepy)4Cl2]+, (2), andtrans-[Co(py4Cl2]+, (3) in the same solvent mixture, shows that the stability increases in the order: (1), (2)<(3) at low mole fraction of the co-solvent, contrary to expectation, while at high mole fraction the order of increasing stability is: (1)<(3)<(2). The results were interpreted on non-electrostatic grounds.