Substitution Reactions of Oxalato Complex Ions. Ii. Kinetics of Aquation of Trisoxalatochromium(iii) Ion—solvent Deuterium Isotope Effect

Krishnamurty, Kotra V.; Harris, G. M.

doi:10.1021/j100832a015

Cited by 51 publications

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“…Cr(C204)2(HC204)(H20)2" % Cr(C204)33-+ H30+ (9) condition is assumed for the concentration of the Cr-(C204)2(HC204)(H20)2~complex intermediate, a closed-form rate law may be derived for the equilibration process which has an observed rate constant given by eq 10. In the event that (fc2/ta)[H+] » 1, eq 10 then reverts to eq 11.…”

Section: Resultsmentioning

confidence: 99%

Reactions of the trans- and cis-diaquobis(oxalato)chromate(III) ions in solutions which contain oxalic acid

Kallen¹

1976

Inorg. Chem.

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When t/'iZZM-Cr(C204)2(H20)2-is added to acidic solutions that contain H2C2O2 and HC2O4-, rapid isomerization of the trans complex occurs. This step is followed by the slower anation of the resulting cis complex by oxalate species. Anation proceeds to an equilibrium mixture of species described by the equilibrium quotient Ki = [Cr(C2CU)33-] [H+]2/ [cis-Cr(C204)2(H20)2-][H2C204]. At 50°C and µ = 1.00 M, maintained with potassium nitrate, Ks = 0.890 ± 0.012 M. The kinetics of the two-step reaction at µ = 1.00 M, between 35 and 55°C, are reported. Both steps of the reaction obey simple first-order kinetics. Observed pseudo-first-order rate constants for the trans-cis isomerization in sodium perchlorate and potassium nitrate were fit to the form /cobsd = kn2o + £m[M+] + &h[H+], where M is sodium or potassium. Activation enthalpies for the various constants are 15.1 ± 0.5 (fcNa), 14.7 ± 0.8 (kt0, and 18.5 ± 0.3 (ku) kcal/mol. Activation entropies are -23.9 ± 1.6 (kNa), -26.0 ± 2.6 (/ck), and -8.5 ± 0.8 (kn) cal/(mol deg). Data interpretations are based on AH* = 17.9 kcal/mol and AS* = -14.7 ca!/(mole deg) for Zch20. Hydrogen ion and ligand dependencies of the observed pseudo-first-order anation rate constants are medium-dependent and slower rates are observed in perchlorate media. In perchlorate media, Zcobsd = /cb[HC204"] + Zc4[H+], while in nitrate media, Acobsd = {/ci[H2C2O4] + (/:2/:4//c3)[H+]2|/|l + (k2//£3)[H+]|. At 50°C in potassium nitrate, k\ = 2.84 X 10-2 AH sec-1, ki/ki = 73.8 ± 11.3 M-1, and ¿4 = 4.38 X 10-4 AH sec-1. Activation enthalpies are 20.7 ± 0.4 and 21.9 ± 0.4 kcal/mol, and activation entropies are -1.9 ± 1.0 and -6.5 ± 1.4 cal/(mol deg), for k] and /c4, respectively. A steady-state mechanism, which describes k 1 and ki as anation steps and ki and ¿4 as aquation steps, is proposed for the anation reaction in both media. This mechanism identifies kb as a composite constant equal to ktks/kiKt, where K\ is the first dissociation constant of oxalic acid. The anation rate constant, k\, is limited by kn for the trans-cis isomerization. Other mechanistic similarities between the isomerization process and aquation and anation processes are described, and a new conformation for the bidentate oxalate ligand is proposed as a precursor to each process.

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Section: Resultsmentioning

confidence: 99%

Reactions of the trans- and cis-diaquobis(oxalato)chromate(III) ions in solutions which contain oxalic acid

Kallen¹

1976

Inorg. Chem.

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“…Even though Cr-0 bonds are involved in both cases, thermal racemization32 of Cr(C204)33-is faster, by several orders of magnitude, than similar processes in /3-diketonate chelates,7 and a factor of ca. 104 separates the aquation rates of Cr(C204)33- 33 and Cr(acac)3. Formation of LF excited states would not significantly perturb the x delocalization which lends unusual stability to the ground state.…”

Section: Discussionmentioning

confidence: 99%

Photochemical and thermal reactions of tris(acetylacetonato)chromium(III) in water-ethanol solution

Zinato¹,

Riccieri²,

Sheridan³

1979

Inorg. Chem.

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on A and B, e is the dielectric constant of the fluid, a is the distance of closest approach of A and B, and the other constants have their usual meanings.hexachloro complex. (17) See, for example, C. H. Langford and J. P. H. Tong, Acc. Chem. Res., 10, 258 (1977). (18) This ratio was calculated by use of the data given by Palmer and Harris' for the cis tetrachloro complex, by W. Robb and M. M. de V. Steyn, Contribution from the Irradiation of 50% v/v water-ethanol solutions of Cr(acac)j at 16 wavelengths between 230 and 730 nm leads to replacement of one acetylacetonate ligand by two water molecules. The photoproduct is cationic, neutral, or anionic depending on solution p H and was characterized by absorption spectra, chemical analysis, ion exchange, and conductivity. The photoaquation quantum yields are pH independent between p H 0 and p H 13, are wavelength independent between 350 and 730 nm, and are atypically low for a Cr(II1) complex (4 = 0.01). A fourfold increase in quantum yield is observed upon 250-nm excitation, with no evidence for redox processes. The system is photochromic, as photoinduced acetylacetonate labilization is opposed by thermal anation of acetylacetone, and photostationary states can occur. The results are interpreted in terms of two distinct reactive excited states: a relatively unreactive ligand field (LF) state and a higher energy ligand-localized (LL) state. IntroductionThe remarkable stability,] t h e well-characterized structural properties,* absorption3 and emission4 spectra, and the variety of electronic transitions make tris(acety1acetonato)chromium(II1) especially interesting from a photochemical point of view.5 Previous investigations of Cr(acac), and of other, variously substituted, P-diketonatochromium(II1) chelates have focused on p h o t o i s~m e r i z a t i o n~~~ and on partial photoresolution.8-12 These studies, however, have been performed in organic, noncoordinating media such as h e~a n e ,~.~ benzene,'O and c h l o r~b e n z e n e ,~~~~~~ where only intramolecular processes (either twisting or bond rupture and recoordination) are possible.An u n d e r s t a n d i n g of t h e photochemical behavior of Cr-(acac), in a coordinating solvent is i m p o r t a n t for a n u m b e r of reasons. (i) The solvent is t h o u g h t to play a crucial role in t h e photochemical reactivity of many Cr(II1) c~m p l e x e s , '~ so studies in noncoordinating solvents exclude a n i m p o r t a n t reactant. (ii) The exceptional inertness' and extensive Telectron system'-3 of the acetylacetonato ligand introduce factors which are rather u n u s u a l in photochemical studies of chromium(III).'3 (iii) The diversity of t h e absorption spectrum gives access to several types of electronic excitation, corresponding t o ligand field (LF), charge-transfer (CT), a n d ligand-localized (LL) transitions.s Selective irradiation may

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“…The syntheses with gadolinium(III) and chromium(III) produced colourless crystals of the binuclear complex [{Gd(bbpen)} 2 (-ox)]Á4CH 3 OHÁ4H 2 O, as revealed by single crystal X-ray diffraction analysis. The formation of this dimer is explained by dissociation of [Cr(ox) 3 ] 3into {Cr(ox) 2 (OH 2 ) 2 } À and ox 2in aqueous solution (Krishnamurty & Harris, 1960), followed by interaction of the ox 2anion with Gd(bbpen) + . Structural elucidation of this otherwise unexpected product prompted us to try and perform its targeted preparation with both gadolinium(III) and dysprosium(III) in good yields.…”

Section: Chemical Contextmentioning

confidence: 99%

Crystal structures of binuclear complexes of gadolinium(III) and dysprosium(III) with oxalate bridges and chelating N,N′-bis(2-oxidobenzyl)-N,N′-bis(pyridin-2-ylmethyl)ethylenediamine (bbpen²⁻)

et al. 2019

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The reaction between mononuclear [Ln(bbpen)Cl] [Ln = Gd or Dy; H2bbpen = N,N′-bis(2-hydroxybenzyl)-N,N′-bis(pyridin-2-ylmethyl)ethylenediamine, C28H30N4O2] and potassium oxalate monohydrate in water/methanol produced the solvated centrosymmetric isostructural binuclear (μ-oxalato)bis{[N,N′-bis(2-oxidobenzyl-κO)-N,N′-bis(pyridin-2-ylmethyl-κN)ethylenediamine-κ2 N,N′]dilanthanide(III)}–methanol–water (1/4/4) complexes, [Ln 2(C28H28N4O2)2(C2O4)]·4CH3OH·4H2O, with lanthanide(III) = gadolinium(III) (Ln = Gd) and dysprosium(III) (Ln = Dy), in high yields (ca 70%) directly from the reaction mixtures. In both complexes, the lanthanide ion is eight-coordinate and adopts a distorted square-antiprismatic coordination environment. The triclinic (P\overline{1}) unit cell contains one dimeric unit together with four water and four methanol molecules; in the final structural model, two of each type of solvating molecule refine well. In each lanthanide(III) dimeric molecule, the medium-strength O...H—O hydrogen-bonding pattern involves four oxygen atoms, two of them from the phenolate groups that are `bridged' by one water and one methanol molecule. These interactions seem to contribute to the stabilization of the relatively compact shape of the dimer. Electron densities associated with an additional water and methanol molecule were removed with the SQUEEZE procedure in PLATON [Spek (2015). Acta Cryst. C71, 9–18]. These two new compounds are of interest with respect to magnetic properties.

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Substitution Reactions of Oxalato Complex Ions. Ii. Kinetics of Aquation of Trisoxalatochromium(iii) Ion—solvent Deuterium Isotope Effect

Cited by 51 publications

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Reactions of the trans- and cis-diaquobis(oxalato)chromate(III) ions in solutions which contain oxalic acid

Reactions of the trans- and cis-diaquobis(oxalato)chromate(III) ions in solutions which contain oxalic acid

Photochemical and thermal reactions of tris(acetylacetonato)chromium(III) in water-ethanol solution

Crystal structures of binuclear complexes of gadolinium(III) and dysprosium(III) with oxalate bridges and chelating N,N′-bis(2-oxidobenzyl)-N,N′-bis(pyridin-2-ylmethyl)ethylenediamine (bbpen²⁻)

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Substitution Reactions of Oxalato Complex Ions. Ii. Kinetics of Aquation of Trisoxalatochromium(iii) Ion—solvent Deuterium Isotope Effect

Cited by 51 publications

References 0 publications

Reactions of the trans- and cis-diaquobis(oxalato)chromate(III) ions in solutions which contain oxalic acid

Reactions of the trans- and cis-diaquobis(oxalato)chromate(III) ions in solutions which contain oxalic acid

Photochemical and thermal reactions of tris(acetylacetonato)chromium(III) in water-ethanol solution

Crystal structures of binuclear complexes of gadolinium(III) and dysprosium(III) with oxalate bridges and chelating N,N′-bis(2-oxidobenzyl)-N,N′-bis(pyridin-2-ylmethyl)ethylenediamine (bbpen2−)

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Crystal structures of binuclear complexes of gadolinium(III) and dysprosium(III) with oxalate bridges and chelating N,N′-bis(2-oxidobenzyl)-N,N′-bis(pyridin-2-ylmethyl)ethylenediamine (bbpen²⁻)