ISSN:
1572-901X
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Summary The reversible complex formation between 2-(2-aminoethyl) benzimidazole (AEB) and nickel(II) was studied by stopped flow spectrophotometry at I = 0.30 mol dm−3. Both the neutral and monoprotonated form of AEB reacted to give the NiAEB2+ chelate. At 25 °C, the rates and activation parameters for the reactions NiII + AEB $$\xrightarrow{{k_f^L }}$$ NiAEB2+ and NiII + AEBH+ $$\xrightarrow{{k_f^{HL} }}$$ NiAEB2+ + H+ are k f L(dm−3 mol−1 s−1) = (2.17 ± 0.24) × 103, ΔH ≠ (kJ mol−1) = 40.0 ± 0.8, ΔS ≠ (JK−1 mol−1) = − 47 ± 3 and k inff pHL (dm3 mol−1 s−1) = 33 ± 10, ΔH ≠(kJ mol−1) = 42.0 ±2.7, ΔS ≠(JK−1 mol−1) = − 72 ± 9. The dissociation of NiAEB2+ was acid catalysed and k obs for this process increased linearly with [H+] in the 0.01–0.15 mol dm−3 (10–30 °C) range with k H(dm3 mol−1s−1) (25 °C) = 329 ± 6, ΔH ≠(kJ mol−1) = 40 ± 2 and ΔS ≠ (JK−1 mol−1) = − 61 ± 8. The results also indicated that the formation of NiAEB2+ involves a chelation-controlled, rate-limiting process. Analysis of the ΔS ° data for the acid ionisation of AEBH inf2 p2+ and the formation of NiAEB2+ showed that the bulky AEBH+ ion has a solvent structure breaking effect as compared to AEB [s aqS ° (AEBH+) − s aq ° (AEB) = 69 JK−1 mol−1], while AEBH inf2 p2+ is a solvent ordering ion relative to NiAEB2+ [s aq° (NiAEB2+) − ovS aq ° (AEBH inf2 p2+ ) = 11 JK−1 mol−1].
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00167018
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