D. A. Palmer
Goethe University Frankfurt
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Review of Scientific Instruments | 1993
R. Van Eldik; Wolfgang Gaede; S. Wieland; Jochen Kraft; M. Spitzer; D. A. Palmer
A modified high‐pressure, stopped‐flow apparatus has been developed to enable kinetic experiments to be monitored spectrophotometrically to 200 MPa, with efficient mixing of the reactant solutions. This apparatus is compact, relatively inexpensive to construct, and the solutions are only exposed to inert materials, such as Kel‐F, Teflon, quartz (low‐pressure windows), and glass or Viton. The drive‐syringe pistons are propelled by a step motor housed on top of the stopped‐flow unit inside the pressure vessel, resulting in a dead time for the system of ∼10 ms at 25 °C.
Inorganica Chimica Acta | 1981
R. Van Eldik; D. A. Palmer; R. Schmidt; H. Kelm
Abstract The kinetics of anation of Pd(1,1,7,7-Et 4 dien)OH 2+ 2 and Pd(1,1,4-Et 3 dien)OH 2+ 2 by chloride ion were studied under pressures up to 1 kbar using a high pressure stopped-flow system. The construction and testing of the latter system are discussed in detail. The rate and activation parameters for the above reactions are: k(25 °C) = 4.2 ± 0.1 and 1558 ± 68 M −1 sec −1 ; ΔH≠ = 13.4 ± 0.4 and 10.5 ± 0.7 kcal mol −1 ; ΔS≠ = −10.7 ± 1.2 and −8.7 ± 2.3 cal K −1 mol −1 ; and ΔV≠ = −3.0 ± 0.2 and −2.7 ± 0.2 cm 3 mol −1 , respectively. These are considered as evidence for an associative type of anation process.
Inorganica Chimica Acta | 1978
M. Mares; D. A. Palmer; H. Kelm
Abstract The pressure and temperature dependencies of the rates of linkage isomeration of the complexes, M(NH 3 ) 5 ONO 2+ , where M represents Co(III), Rh(III) and Ir(III), were mesured in aqueous solution at an ionic strength of 0.1 M . The volumes of activation were found to be −6.7 ± 0.4, −7.4 ± 0.4 and −5.9 ± 0.6 cm 3 mol −1 , resp. Partial molar volumes of the nitrito- and nitro-pentaamminecobalt(III) cations were determined at 82.3 ± 1.4 and 69.4 ± 0.1 cm 3 mol −1 . The volume profile for this reaction indicates the mechanism to be intramolecular in agreement with previous work [1, 2].
Inorganica Chimica Acta | 1976
D. A. Palmer; H. Kelm
Abstract The effect of pressure on the substitution reactions of [Pt(dien)X] + complexes (dien = diethylenetriamine) with a number of nucleophiles, Y, have been studied in aqueous solution at 25°C and an ionic strength of 0.2M, where X = Cl − , Br − , I − , N 3 − and Y = Oh − , I − , N 3 − , NO 2 − , SCN − and pyridine. The volumes of activation are all negative with the mean value for the nucleophile independent path being –18±2 ml mol −1 . Partial molar volumes of the respective substrates and products were measured at 25°C. The data are discussed in terms of an associative mechanism for the nucleophile dependent path, while for the independent path both associative and dissociative mechanisms are considered.
Inorganica Chimica Acta | 1982
Georg Daffner; D. A. Palmer; H. Kelm
Abstract The pressure, temperature and pH dependencies of the rate of aquation of a range of trans-complexes with the general formula CoN4X+2 were studied where X = Cl and N4 ≡ (NH3)4; (en)2; R,S-(2,3,2-tet); RR,SS-(2,3,2-tet); (Meen)2; (Eten)2; (Pren)2; (3,2,3-tet); (2,3,2-tet); (cyclam); and X= Br, N4 ≡ (en)2; (2,3,2-tet); (3,2,3-tet). The ΔVne values for all the dichloro complexes, including cis-Co(en)2Cl+2 averaged −1.4 ± 1.0 cm3 mol−1 which was interpreted in terms of an Id mechanism. The slightly more positive ΔV≠ values for the dibromo species are also consistent with this mechanism. The aquation of the trans-Co(NH3)4CN(X)+ complexes, where X = Cl, Br, I, N3 and DMSO, was also considered to involve a similar mechanism, although in this case it possesses significantly more associative character.
Inorganica Chimica Acta | 1978
D. A. Palmer; R. Schmidt; R. Van Eldik; H. Kelm
Abstract The kinetics of anation of Pd(MeEt 4 dien)OH 2+ 2 by chloride ion were studied under the following conditions: 0,011 ≤ [Cl − ] ≤ 0,081 M ; 15 ≤ temperature ≤ 35°C; 1 ≤ pressure ≤ 1000 bar; [H + ] = 2.5 × 10 −3 M (HClO 4 ) and ionic strength 0,1 M (NaClO 4 ). The [Cl − ] and temperature dependencies of the reaction rate were investigated at 500 bar. A high pressure rapid mixing system was used in these studies and is described in detail. Mixing of the pressurized reactant solutions can be accomplished within five seconds so that reactions with half-lives in the order of ten seconds can be measured accurately. The activation parameters for the title reaction are considered as evidence for an associative mechanism, possibly of the I a type.
Inorganica Chimica Acta | 1978
R. Van Eldik; D. A. Palmer; H. Kelm
Abstract The kinetics of reduction of Co(NH 3 ) 5 F 2+ , Co(NH 3 ) 5 Cl 2+ and Co(NH 3 ) 5 Br 2+ by Fe(II) have been studied at 35°C as a function of pressure up to 1,7 kbar. The volumes of activation were independent of pressure and found to be +10,3 ± 0,4; +3,8 ± 0,7 and 0,0 ± 0,4 cm 3 mol −1 for the three systems, respectively. The results are discussed with reference to earlier work reported in literature. Changes in solvation and possible steric requirements can account for the observed kinetic parameters.
Inorganica Chimica Acta | 1978
D. A. Palmer; R. Van Eldik; H. Kelm
Abstract Pressure and temperature dependncies of the rate of linkage isomerization of Co(NH 3 ) 5 SCN 2+ in acidic aqueous solution yielded the activation parameters: ΔH‡ = 102.8 ± 0.8 kJ mol −1 ; ΔS‡ = −14 ± 3J K −1 mol −1 ; ΔV‡ = −5.3 ± 0.8 cm 3 mol −1 . A similar study in DMSO resulted in the following parameters: ΔH‡ = 105 ± 2 kJ mol −1 ; ΔS‡ = −2 ± 4J K −1 mol −1 ; ΔV‡ exp = −1.0 ± 1.2 cm 3 mol −1 . These values emphasize that the rearrangement are intramolecular. They exclude the possibility that an “intimate ion-pair” it involved and rather suggest that the reactions proceed via a !abile intermediate in which cobalt is bound to thiocyanate through a filled π orbital.
Inorganica Chimica Acta | 1979
D. A. Palmer; R. Van Eldik; T. P. Dasgupta; H. Kelm
Abstract The pressure dependencies of the rates of Hg(II) induced aquation of Co(NH 3 ) 5 Cl 2+ , CoNH 3 5 Br 2+ Cr(NH 3 ) 5 Cl 2+ , and Rh(NH 3 ) 5 Cl 2+ were studied at 15°C, with the exception of the latter which was investigated at 25°C, and a [H + ] of 0.31 M with μ = 0.6 M . The respective volumes of activation were found to be −1.7 ± 1.0, +0.8 ± 0.5, +0.7 ± 0.4, and −1.0 ± 0.4 cm 3 mol −1 . These results are discussed with reference to the numerous conventional kinetic data in the literature, further establishing a D-mechanism for the rate-determining step.
Inorganica Chimica Acta | 1980
D. A. Palmer; H. Kelm
Abstract The pressure dependencies of the rates of solvolysis of [Pd(Et4dien)I]+ in the presence of 0.05 M Br− were measured in methanol, ethanol, dimethyl sulfoxide, N,N-dimethylformamide and acetonitrile at 40 °C. The respective volumes of activation are −13.4 ± 0.5, −12.9 ± 0.4, −10.1 ± 0.2, −9.3 ± 0.3 and −7.9 ± 0.5 cm3 mol−1. The temperature depen- dencies of the rate constants were also determined for the solvents acetonitrile, acetone and N,N- dimethylacetamide to supplement the existing data in the remaining solvents. An associative interchange mechanism is favored to explain these results.