Ammine ligand exchange in tetraamminegold(III) in aqueous solution. Composition of transition states and relative reactivity of tetraamminegold(III) and its conjugated base, amidotriamminegold(III)
Journal Article
·
· Inorg. Chem.; (United States)
Temperature dependence of the rate of exchange of ammonia between tetraamminegold(III) and solution ammonia in aqueous ammonium perchlorate of unit ionic strength in the pH range 5-10 has been determined by using nitrogen-15 labeling. At fixed pH, the exchange follows second-order kinetics (first order in both complex and ammonia/ammonium), and the pH dependence of the second-order constant can be accounted for in terms of reactions between the two acids NH/sub 4//sup +/ and Au(NH/sub 3/)/sub 4//sup 3+/ and their conjugated bases NH/sub 3/ and Au(NH/sub 3/)/sub 3/NH/sub 2//sup 2+/, respectively. The direct exchange between NH/sub 4//sup +/ and Au(NH/sub 3/)/sub 4//sup 3+/ is significant but slow (statistically corrected second-order rate constant k = 6.0 (3) /times/ 10/sup /minus/5/ L /times/ mol/sup /minus/1/ /times/ s/sup /minus/1/, /Delta/H/double dagger/ = 84 (2) kJ /times/ mol/sup /minus//1, /Delta/S/double dagger/ = /minus/42 (5) J /times/ mol/sup /minus/1/ at 25/degree/C) compared to the exchange between NH/sub 3/ and Au(NH/sub 3/)/sub 3/NH/sub 2//sup 2+/ (k = 3.9 (2) /times/ 10/sup /minus/2/ L /times/ mol/sup /minus/1/ /times/ s/sup /minus//1, /Delta/H/double dagger/ = 68 (2) kJ /times/ mol/sup /minus/1/, /Delta/S/double dagger/ = /minus/44 (8) J /times/ mol/sup /minus/1/ /times/ K/sup /minus/1/). Exchange via a transition state of the composition (Au(NH/sub 3/)/sub 3/NH/sub 2//hor ellipsis/H/hor ellipsis/NH/sub 3/)/sup 3+/ is significant at intermediate pH, most likely as a result of reaction between NH/sub 3/ and Au(NH/sub 3/)/sub 4//sup 3+/ (k = 1.69 (6) /times/ 10/sup /minus/1/ L /times/ mol/sup /minus/1/ /times/ s/sup /minus/1/, /Delta/H/double dagger/ = 61 (2) kJ /times/ mol/sup /minus//1, /Delta/S/double dagger/ = /minus/ (6) J /times/ mol/sup /minus//1 /times/K/sup /minus/1/). 28 references, 5 figures, 3 tables.
- Research Organization:
- Royal Veterinary and Agricultural Univ., Frederiksberg (Denmark)
- OSTI ID:
- 5845064
- Journal Information:
- Inorg. Chem.; (United States), Journal Name: Inorg. Chem.; (United States) Vol. 27:11; ISSN INOCA
- Country of Publication:
- United States
- Language:
- English
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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
400202 -- Isotope Effects
Isotope Exchange
& Isotope Separation
AMMONIA
AQUEOUS SOLUTIONS
CHEMICAL REACTIONS
COMPLEXES
DATA
DISPERSIONS
EXPERIMENTAL DATA
GOLD COMPLEXES
HYDRIDES
HYDROGEN COMPOUNDS
INFORMATION
ISOTOPES
LABELLED COMPOUNDS
LIGHT NUCLEI
MIXTURES
NITROGEN 15
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NITROGEN ISOTOPES
NUCLEI
NUMERICAL DATA
ODD-EVEN NUCLEI
SOLUTIONS
STABLE ISOTOPES
TRANSITION ELEMENT COMPLEXES
400201* -- Chemical & Physicochemical Properties
400202 -- Isotope Effects
Isotope Exchange
& Isotope Separation
AMMONIA
AQUEOUS SOLUTIONS
CHEMICAL REACTIONS
COMPLEXES
DATA
DISPERSIONS
EXPERIMENTAL DATA
GOLD COMPLEXES
HYDRIDES
HYDROGEN COMPOUNDS
INFORMATION
ISOTOPES
LABELLED COMPOUNDS
LIGHT NUCLEI
MIXTURES
NITROGEN 15
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NITROGEN ISOTOPES
NUCLEI
NUMERICAL DATA
ODD-EVEN NUCLEI
SOLUTIONS
STABLE ISOTOPES
TRANSITION ELEMENT COMPLEXES