Kinetic studies on the substitution reactions of (Pyridine-2-carbaldehyde 2'-pyridylhydrazone)nickel(II). A study of stacking interactions in outer-sphere complexes

1980 ◽  
Vol 33 (1) ◽  
pp. 45 ◽  
Author(s):  
RW Renfrew ◽  
P Osvath ◽  
DC Weatherburn
Keyword(s):  
Water Loss ◽  
Kinetic Studies ◽  
Outer Sphere ◽  
Ternary Complexes ◽  
Ring Closure ◽  
Stacking Interactions ◽  
Substitution Reactions ◽  
Loss Mechanism ◽  
Kinetics Of ◽  
Outer Sphere Complexes

Kinetics of the formation reactions of the mono and bis complexes of pyridine-2-carbaldehyde 2'-pyridylhydrazone (paphy) with nickel((II), the mono complex of 6-methylpyridine-2-carbaldehyde2'-pyridylhydrazone (mpaphy) with nickel(II), and of the ternary complexes of Ni(paphy)2+ with terpy, bpy, phen and pada and Ni(paphy)2+ and Ni(phen)2+ with mpaphy have been studied inaqueous solution at 25°C and ionic strength 0.1 mol dm-3 (NaNO3). The rates of the formationreactions of the mono complexes are slower than expected on the basis of the usual water-loss mechanism, and ring closure probably contributes to the observed rates. The formation of the bisand ternary complexes is usually more rapid than predicted by the water-loss mechanism. The enhanced rates are attributed to large outer-sphere association constants due to 'stacking' interactions between the incoming and bound ligands.

scholarly journals Investigations of ternary complexes of Co(II) and Ni(II) with oxydiacetate anion and 1,10-phenanthroline or 2,2′-bipyridine in solutions

2014 ◽  
Vol 12 (1) ◽  
pp. 107-114 ◽  
Author(s):  
Dariusz Wyrzykowski ◽  
Joanna Pranczk ◽  
Dagmara Jacewicz ◽  
Aleksandra Tesmar ◽  
Bogusław Pilarski ◽  
...  
Keyword(s):  
Formation Constants ◽  
Ternary Complexes ◽  
Substitution Reactions ◽  
Constant Concentration ◽  
Experimental Conditions ◽  
Kinetic Measurements ◽  
Binary Complexes ◽  
The Stability ◽  
Kinetics Of ◽  
Complex Formation Process

AbstractPotentiometric (PT) and conductometric (CT) titration methods have been used to determine the stoichiometry and formation constants in water for a series of ternary complexes of Co(II) and Ni(II) involving the oxydiacetate anion (ODA) and 1,10-phenanthroline (phen) or 2,2′-bipyridine (bipy) ligands, namely [Co(ODA)(phen)(H2O)], [Co(ODA)(bpy)(H2O)], [Ni(ODA)(phen)(H2O)] and [Ni(ODA)(bpy)(H2O)]. The ternary complex formation process was found to take place in a stepwise manner in which the oxydiacetate ligand acts as a primary ligand and the phen or bipy ligands act as auxiliary ones. The stability of the ternary complexes formed is discussed in the relation to the corresponding binary ones. Furthermore, the kinetics of the substitution reactions of the aqua ligands in the coordination sphere of the Ni-ODA and Co-ODA complexes to phen or bipy were studied by the stopped-flow method. The kinetic measurements were performed in the 288–303 K temperature range, at a constant concentration of phen or bipy and at seven different concentrations of the binary complexes (4–7 mM). The influence of experimental conditions and the kind of the auxiliary ligands (phen/bipy) on the substitution rate was discussed.

scholarly journals Kinetic Studies of the Reactions between Dichlorido(1,2-Diaminoethane)Zinc(II) and Biologically Relevant Nucleophiles in the Presence of Chloride

2018 ◽  
Vol 43 (1) ◽  
pp. 53-61 ◽  
Author(s):  
Tanja Soldatović ◽  
Enisa Selimović
Keyword(s):  
Chloride Ion ◽  
Kinetic Studies ◽  
Chloride Ions ◽  
Octahedral Complex ◽  
Ratio Method ◽  
Reaction Step ◽  
Substitution Reactions ◽  
Biologically Relevant ◽  
Additional Coordination ◽  
Kinetics Of

The mole-ratio method was used for determining metal–ligand stoichiometry for the reaction between [ZnCl2(en)] (where en = 1,2-diaminoethane or ethylenediamine) and chloride ion at pH 7.2. The results have shown step-wise formation of 1:1 and 1:2 complexes and indicate additional coordination of chloride ions in the first coordination sphere. The kinetics of ligand substitution reactions of the zinc(II) complex and biologically relevant nucleophiles such as inosine-5′-monophosphate (5′-IMP), guanosine-5′-monophosphate (5′-GMP), L-methionine (L-Met), glutathione (GSH) and DL-aspartic acid (DL-Asp) were investigated at pH 7.2 as a function of nucleophile concentration in the presence of 0.010 M NaCl. The reactions were followed under pseudo first-order conditions by UV-Vis spectrophotometry. The substitution reactions include two steps of consecutive displacement of chlorido ligands and changes in coordination geometry. In the presence of an excess of chloride, the octahedral complex anion [ZnCl4(en)]2- formed. The first step of the substitution reactions could be interpreted as substitution of the axial chlorido ligands in the cis position to bidentate ethylenediamine by the biologically relevant nucleophiles, while the second step could be interpreted as substitution of the equatorial chlorido ligand. The order of reactivity of the investigated nucleophiles for the first reaction step is 5′-IMP > GSH > L-Met > DL-Asp > 5′-GMP, while for the second reaction step the order of reactivity is GSH > L-Met > 5′-IMP > DL-Asp > 5′-GMP.

scholarly journals Ligand substitution kinetics of nickel(II) ion in N,N-dimethylformamide

1977 ◽  
Vol 55 (19) ◽  
pp. 3449-3455 ◽  
Author(s):  
Praphulla Kumar Chattopadhyay ◽  
Byron Kratochvil
Keyword(s):  
Activation Parameters ◽  
Outer Sphere ◽  
Dimethyl Formamide ◽  
Outer Sphere Complex ◽  
Hammett Correlation ◽  
Sphere Complex ◽  
The Stability ◽  
Kinetics Of ◽  
Metal Ligand ◽  
Outer Sphere Complexes

Rate constants and activation parameters for formation of the monocomplexes of Ni(II) ion with several mono-, bi-, and terdentate ligands in N,N-dimethylformamide were obtained by stopped-flow spectrophotometry. The gross features of substitution for all the ligands studied could be accommodated within the structure of an Id-type mechanism. 4-Phenylpyridine behaves most 'normally', and 1,10-phenanthroline stabilized most strongly outer-sphere complex formation with Ni(II). Comparison of these data with previously reported work by other authors for substitution at Ni(II) in acetonitrile with the same ligands indicates that in dimethyl-formamide pyridine-type ligands generally affect the stability of metal–ligand outer-sphere complexes less dramatically than in acetonitrile. Hammett correlation is observed for 1,10-phenanthroline and its 5- and 5,6-substituted derivatives. The slope of the Hammett correlation plot in dimethylformamide is in the order of −0.2, about half the value of −0.4 reported previously in acetonitrile by other authors. This indicates that the stability of the metal–ligand outer-sphere complex is affected more greatly by small differences in the electronic nature of the coordinating substituted 1,10-phenanthrolines in acetonitrile than it is in dimethylformamide.

Evidence for general base catalysis by protic solvents in a kinetic study of alcoholyses and hydrolyses of 1-(phenoxycarbonyl)pyridinium ions under both solvolytic and non-solvolytic conditions

2009 ◽  
Vol 74 (1) ◽  
pp. 43-55 ◽  
Author(s):  
Dennis N. Kevill ◽  
Byoung-Chun Park ◽  
Jin Burm Kyong
Keyword(s):  
Second Order ◽  
Base Catalysis ◽  
Substitution Reactions ◽  
Third Order ◽  
Methoxy Derivative ◽  
First Order ◽  
General Base ◽  
Protic Solvents ◽  
Kinetics Of ◽  
Pyridinium Ions

The kinetics of nucleophilic substitution reactions of 1-(phenoxycarbonyl)pyridinium ions, prepared with the essentially non-nucleophilic/non-basic fluoroborate as the counterion, have been studied using up to 1.60 M methanol in acetonitrile as solvent and under solvolytic conditions in 2,2,2-trifluoroethan-1-ol (TFE) and its mixtures with water. Under the non- solvolytic conditions, the parent and three pyridine-ring-substituted derivatives were studied. Both second-order (first-order in methanol) and third-order (second-order in methanol) kinetic contributions were observed. In the solvolysis studies, since solvent ionizing power values were almost constant over the range of aqueous TFE studied, a Grunwald–Winstein equation treatment of the specific rates of solvolysis for the parent and the 4-methoxy derivative could be carried out in terms of variations in solvent nucleophilicity, and an appreciable sensitivity to changes in solvent nucleophilicity was found.

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