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The impact of tripodal chelates on water exchange kinetics and mechanisms: A variable temperature and pressure 17 O NMR study to clarify the structure‐reactivity relationship in [Fe II (L)(H 2 O) 2 ] − complexes
Author(s) -
Maigut Joachim,
Meier Roland,
Zahl Achim,
van Eldik Rudi
Publication year - 2008
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.2322
Subject(s) - chemistry , reaction rate constant , reactivity (psychology) , analytical chemistry (journal) , kinetics , nuclear magnetic resonance spectroscopy , activation energy , chemical kinetics , chelation , inorganic chemistry , stereochemistry , organic chemistry , medicine , physics , alternative medicine , pathology , quantum mechanics
The effect of temperature and pressure on the water exchange reaction of [Fe II (NTA)(H 2 O) 2 ] − and [Fe II (BADA)(H 2 O) 2 ] − (NTA = nitrilotriacetate; BADA = β‐alanindiacetate) was studied by 17 O NMR spectroscopy. The [Fe II (NTA)(H 2 O) 2 ] − complex showed a water exchange rate constant, k ex , of (3.1 ± 0.4) × 10 6 s −1 at 298.2 K and ambient pressure. The activation parameters ΔH ≠ , ΔS ≠ and ΔV ≠ for the observed reaction are 43.4 ± 2.6 kJ mol −1 , + 25 ± 9 J K −1 mol −1 and + 13.2 ± 0.6 cm 3 mol −1 , respectively. For [Fe II (BADA)(H 2 O) 2 ] − , the water exchange reaction is faster than for the [Fe II (NTA)(H 2 O) 2 ] − complex with k ex = (7.4 ± 0.4) × 10 6 s −1 at 298.2 K and ambient pressure. The activation parameters Δ H ≠ , Δ S ≠ and Δ V ≠ for the water exchange reaction are 40.3 ± 2.5 kJ mol −1 , + 22 ± 9 J K −1 mol −1 and + 13.3 ± 0.8 cm 3 mol −1 , respectively. The effect of pressure on the exchange rate constant is large and very similar for both systems, and the numerical values for Δ V ≠ suggest in both cases a limiting dissociative (D) mechanism for the water exchange process. Copyright © 2008 John Wiley & Sons, Ltd.