Topic
Aquation
About: Aquation is a research topic. Over the lifetime, 1443 publications have been published within this topic receiving 17507 citations.
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TL;DR: A monotonic increase in the extinction coefficient is observed on going from the cyclam complexes to the 1,11-C3-cyclam complexes, and this is related to the degree of centrosymmetry in each complex.
Abstract: The synthesis and characterization of several Cr(III) complexes of the constrained macrocyclic ligand 1,11-C3-cyclam (1,4,8,11-tetraazabicyclo[9.3.3]heptadecane) is reported. Only trans complexes are formed, and the structure of trans-[Cr(1,11-C3-cyclam)Cl2]PF6 is presented. The chemical and photophysical behavior of the 1,11-C3-cyclam complexes are compared with those of the corresponding cyclam (1,4,8,11 tetraazacyclotetradecane) and 1,4-C2-cyclam (1,4,8,11-tetraazabicyclo[10.2.2]hexadecane) complexes. The aquation rate of trans-[Cr(1,11-C3-cyclam)Cl2]+ is similar to that of the corresponding 1,4-C2-cyclam complex and is more than 5 orders of magnitude faster than the cyclam counterpart. A monotonic increase in the extinction coefficient is observed on going from the cyclam complexes to the 1,11-C3-cyclam complexes to the 1,4-C2-cyclam complexes, and this is related to the degree of centrosymmetry in each complex. The trans-[Cr(1,11-C3-cyclam)(CN)2]+ complex is a weak emitter in aqueous solution with a room-temperature emission maximum at 724 nm (tau=23 micros). Like the corresponding 1,4-C2-cyclam complex (tau=0.24 micros), the 1,11-C3-cyclam complex shows no deuterium-isotope effect in room-temperature solution. This is in marked contrast to the corresponding cyclam complex which has an emission lifetime of 335 micros and a significant deuterium isotope effect in room-temperature solution. Low temperature (77K) data are also presented in an attempt to understand the differences in photophysical behavior.
18 citations
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Abstract: Kinetics and equilibria for reversible formation of 1:1 monodentate complexes between Pd(H2O)42+ and acetic, propionic, and glycolic acid (RCOOH) according to the equation Pd(H2O)42+ + RCOOH ⇌ Pd(H2O)3OOCR+ + H3O+ (k1, k-1) have been studied as a function of temperature and pressure in an aqueous medium with 0.60 ≤ [H+] ≤ 1.00 M, [RCOOH]/[H+] ≤ 1.0, and ionic strength 1.00 M. Stability constants β1 for the formation of acetate, propionate, and glycolate complexes are (2.19 ± 0.09) × 104, (2.10 ± 0.24) × 104, and (6.4 ± 0.1) × 103 M-1, repectively, at 25 °C and for a 1.00 M perchlorate medium. The rate expression, kobsd = k1[RCOOH] + k-1[H+], indicates that reaction between palladium and carboxylate anions is negligible under the experimental conditions used. Values for k1/M-1 s-1, k-1/M-1 s-1, ΔH1⧧/kJ mol-1, ΔH-1⧧/kJ mol-1, ΔS1⧧/J K-1 mol-1, ΔS-1⧧/J K-1 mol-1, ΔV1⧧/cm3 mol-1, and ΔV-1⧧/cm3 mol-1 at 25.0 °C are 19.3 ± 0.6, 32.8 ± 0.2, 52.5 ± 0.4, 57.5 ± 0.4, −44 ± 1, −23 ± 1, −8.1 ± 0.3, and −1.7 ± 0.2 for...
18 citations
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TL;DR: In this paper, a number of new diphosphine complexes of cobalt(III), trans- and cis-[CoCl2(dmpe, dmpp, dbpe, or dpee)2]+ have been prepared and characterized.
Abstract: A number of new diphosphine complexes of cobalt(III), trans- and cis-[CoCl2(dmpe, dmpp, dbpe, or dpee)2]+, trans- and cis-[CoBr2(dmpe)2]+, trans- and cis-[CoCl(H2O)(dmpe)2]2+, trans-[Co(I2 or BrI)(dmpe)2]+, and [Co(CO3)(dmpp or dbpe)]+ have been prepared and characterized, where dmpe, dmpp, dbpe, and dpee denote 1,2-bis(dimethylphosphino)ethane, 1,3-bis(dimethylphosphino)propane, 1,2-bis(dibutylphosphino)ethane, and cis-1,2-bis(diphenylphosphino)ethylene, respectively. The trans isomers of the dihalogeno complexes are stable to aquation, while the cis isomers release one of the halide ions in water fairly rapidly to yield cis-[CoX(H2O)(diphosphine)2]+ which isomerizes to the trans isomer on exposure of ultraviolet light. The cis-[CoCl2(diphosphine)2]+ complexes in methanol or ethanol solution isomerize to the trans isomer, and the rates were followed spectrophotometrically in the temperature range of 39.0–65.0 °C. The rates have a first-order dependence on the complex concentration. Both the ΔH\eweq and Δ...
17 citations
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TL;DR: In this article, the photochemical decomposition of dilute HCl, HClO4 and H2SO4 solutions has been studied and the yield of each species as a function of the time of uv irradiation was determined.
Abstract: The photochemical decomposition of (NH4)2TcCl6 in dilute HCl, HClO4 and H2SO4 solutions has been studied. Electrophoresis and spectrophotometry were used to identify TcCl
6
2−
, TcCl5 (H2O)−, cationic and uncharged species and TcO
4
−
. The yield of each species as a function of the time of uv irradiation was determined. The TcCl
6
2−
, yield decreases to zero after 50 h of irradiation. The TcCl5(H2O)−, cationic and uncharged species and TcO
4
−
are formed in different proportions in the three acids. After 120 h of irradiation of the HCl solution the principal Tc species was the cationic one (≈70%) followed by the uncharged species (≈24%). In HClO4 solution the cationic species (≈70%) was followed by TcO
4
−
, but in H2SO4 solution the uncharged species amounts to ≈90%.
17 citations
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TL;DR: In this paper, the rates of release of fiuoride by acid and base hydrolysis of cis-STACr(en)/sub 2/F/ sub 2/O)F!/sup 2+/ were determined over a range of pH 1 to 8.
Abstract: The rates of release of fiuoride by acid and base hydrolysis of cis- STACr(en)/sub 2/F/sub 2/!/sup +/ were determined over a range of pH 1 to 8. At 25 deg the pseudo first-order aquation rate constant for loss of the first fiuoride in 0.1 f HClO/sub 4/ is 5.3 x 10/sup -6/ sec/sup -1/, much less than the corresponding rate constants of cis-STACo(en)/sub 2/F/sub 2/!/sup +/ and cis- STACr(en)/sub 2/Cl/sub 2/!/sup +/ in 0.1 f HNO/sub 3/ . The Arrhenius activation energy is 23 plus or minus 1 kcal./mole. The aquation of cis-STACr(en)/sub 2/F/ sub 2/!/sup +/ is acid catalyzed like the cobalt analog but, unlike the dichloro cobalt and chromium analogs, presumably because the difiuoro complexes aquate by a mechanism involving an intermediate reactive protonated complex. Cation- exchange and spectral evidence indicate that the aquation product is largely, if not entirely, cisSTACr(en)/sub 2/(H/sub 2/O)F!/sup 2+/. Fluoride is taken up by one or more reaction products in later stages of the hydrolysis. The aquation appears not to be accelerated by visible light. (auth)
17 citations