Kinetics and mechanism of ligand interchange in pentacyano-L-osmate(II) complexes (L = H2O, NH3, N-heterocyclic ligands
The new complex, K3[Os(CN)5NH3]·2H2O, a convenient precursor for the pentacyano-L-osmate(II) series, was prepared and characterized by chemical analysis, cyclic voltammetry, and IR and UV-vis spectroscopies. By controlled aquation in weakly acidic medium, the [Os(CN)5H2O]3- ion was generated. Weak a...
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todo:paper_00201669_v41_n1_p114_Slep2023-10-03T14:16:51Z Kinetics and mechanism of ligand interchange in pentacyano-L-osmate(II) complexes (L = H2O, NH3, N-heterocyclic ligands Slep, L.D. Alborés, P. Baraldo, L.M. Olabe, J.A. ammonia heterocyclic compound iron derivative isonicotinamide isonicotinic acid ligand nitrile osmium derivative pyrazine derivative pyridine derivative ruthenium derivative water acidity article chemical analysis chemical reaction kinetics cyclic potentiometry dissociation enthalpy entropy infrared spectroscopy synthesis ultraviolet spectroscopy The new complex, K3[Os(CN)5NH3]·2H2O, a convenient precursor for the pentacyano-L-osmate(II) series, was prepared and characterized by chemical analysis, cyclic voltammetry, and IR and UV-vis spectroscopies. By controlled aquation in weakly acidic medium, the [Os(CN)5H2O]3- ion was generated. Weak absorptions in the UV region for L = H2O, NH3, and CN- were found at 287, 272, and 240 nm, respectively, and were assigned to d-d transitions, in terms of a model for tetragonally distorted ions also valid for the members of the iron and ruthenium series. The kinetics of the formation and dissociation reactions of the [Os(CN)5L]n- ions, L = pyridine (py), pyrazine (pz), N-methylpyrazinium (mpz+), etc., were studied. At 25.0 °C, the formation rate constants for the neutral ligands pz and isonicotinamide were ca. 0.13 M-1 s-1 and slightly increased for L = mpz+ and decreased for isonicotinate. The enthalpies of activation were ca. 22.0 kcal mol-1, independently of the entering L, and the activation entropies were all positive, ca. 11-13 cal K-1 mol-1. The dissociation reactions showed a saturation rate behavior of kobs (s-1) as a function of the concentration of the scavenger ligand. The specific dissociation rate constant at 25.0 °C was 1.06 × 10-7 s-1 for L = NH3 and around 10-9 s-1 for py, pz, and mpz+ (extrapolated to 25.0 °C from values measured in the range 60-95 °C). These small values are associated with high activation enthalpies (range 30-35 kcal mol-1) and positive activation entropies (range 10-20 cal K-1 mol-1). The evidence for both the formation and dissociation processes shows that dissociative mechanisms are operative, as for the iron and ruthenium analogues. Fil:Slep, L.D. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Fil:Alborés, P. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Fil:Baraldo, L.M. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Fil:Olabe, J.A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. JOUR info:eu-repo/semantics/openAccess http://creativecommons.org/licenses/by/2.5/ar http://hdl.handle.net/20.500.12110/paper_00201669_v41_n1_p114_Slep |
| institution |
Universidad de Buenos Aires |
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I-28 |
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R-134 |
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Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) |
| topic |
ammonia heterocyclic compound iron derivative isonicotinamide isonicotinic acid ligand nitrile osmium derivative pyrazine derivative pyridine derivative ruthenium derivative water acidity article chemical analysis chemical reaction kinetics cyclic potentiometry dissociation enthalpy entropy infrared spectroscopy synthesis ultraviolet spectroscopy |
| spellingShingle |
ammonia heterocyclic compound iron derivative isonicotinamide isonicotinic acid ligand nitrile osmium derivative pyrazine derivative pyridine derivative ruthenium derivative water acidity article chemical analysis chemical reaction kinetics cyclic potentiometry dissociation enthalpy entropy infrared spectroscopy synthesis ultraviolet spectroscopy Slep, L.D. Alborés, P. Baraldo, L.M. Olabe, J.A. Kinetics and mechanism of ligand interchange in pentacyano-L-osmate(II) complexes (L = H2O, NH3, N-heterocyclic ligands |
| topic_facet |
ammonia heterocyclic compound iron derivative isonicotinamide isonicotinic acid ligand nitrile osmium derivative pyrazine derivative pyridine derivative ruthenium derivative water acidity article chemical analysis chemical reaction kinetics cyclic potentiometry dissociation enthalpy entropy infrared spectroscopy synthesis ultraviolet spectroscopy |
| description |
The new complex, K3[Os(CN)5NH3]·2H2O, a convenient precursor for the pentacyano-L-osmate(II) series, was prepared and characterized by chemical analysis, cyclic voltammetry, and IR and UV-vis spectroscopies. By controlled aquation in weakly acidic medium, the [Os(CN)5H2O]3- ion was generated. Weak absorptions in the UV region for L = H2O, NH3, and CN- were found at 287, 272, and 240 nm, respectively, and were assigned to d-d transitions, in terms of a model for tetragonally distorted ions also valid for the members of the iron and ruthenium series. The kinetics of the formation and dissociation reactions of the [Os(CN)5L]n- ions, L = pyridine (py), pyrazine (pz), N-methylpyrazinium (mpz+), etc., were studied. At 25.0 °C, the formation rate constants for the neutral ligands pz and isonicotinamide were ca. 0.13 M-1 s-1 and slightly increased for L = mpz+ and decreased for isonicotinate. The enthalpies of activation were ca. 22.0 kcal mol-1, independently of the entering L, and the activation entropies were all positive, ca. 11-13 cal K-1 mol-1. The dissociation reactions showed a saturation rate behavior of kobs (s-1) as a function of the concentration of the scavenger ligand. The specific dissociation rate constant at 25.0 °C was 1.06 × 10-7 s-1 for L = NH3 and around 10-9 s-1 for py, pz, and mpz+ (extrapolated to 25.0 °C from values measured in the range 60-95 °C). These small values are associated with high activation enthalpies (range 30-35 kcal mol-1) and positive activation entropies (range 10-20 cal K-1 mol-1). The evidence for both the formation and dissociation processes shows that dissociative mechanisms are operative, as for the iron and ruthenium analogues. |
| format |
JOUR |
| author |
Slep, L.D. Alborés, P. Baraldo, L.M. Olabe, J.A. |
| author_facet |
Slep, L.D. Alborés, P. Baraldo, L.M. Olabe, J.A. |
| author_sort |
Slep, L.D. |
| title |
Kinetics and mechanism of ligand interchange in pentacyano-L-osmate(II) complexes (L = H2O, NH3, N-heterocyclic ligands |
| title_short |
Kinetics and mechanism of ligand interchange in pentacyano-L-osmate(II) complexes (L = H2O, NH3, N-heterocyclic ligands |
| title_full |
Kinetics and mechanism of ligand interchange in pentacyano-L-osmate(II) complexes (L = H2O, NH3, N-heterocyclic ligands |
| title_fullStr |
Kinetics and mechanism of ligand interchange in pentacyano-L-osmate(II) complexes (L = H2O, NH3, N-heterocyclic ligands |
| title_full_unstemmed |
Kinetics and mechanism of ligand interchange in pentacyano-L-osmate(II) complexes (L = H2O, NH3, N-heterocyclic ligands |
| title_sort |
kinetics and mechanism of ligand interchange in pentacyano-l-osmate(ii) complexes (l = h2o, nh3, n-heterocyclic ligands |
| url |
http://hdl.handle.net/20.500.12110/paper_00201669_v41_n1_p114_Slep |
| work_keys_str_mv |
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| _version_ |
1807321148500738048 |