Maigut Joachim, Meier Roland, Zahl Achim, van Eldik Rudi
Institute for Inorganic Chemistry, University of Erlangen-Nürnberg, Egerlandstrasse 1, 91058 Erlangen, Germany.
Inorg Chem. 2007 Jun 25;46(13):5361-71. doi: 10.1021/ic700472q. Epub 2007 May 27.
The lability and structural dynamics of Fe(II)(edta)(H(2)O) (edta = ethylenediaminetetraacetate) in aqueous solution strongly depend on solvent interactions. To study the solution structure and water-exchange mechanism, (1)H, (13)C, and (17)O NMR techniques were applied. The water-exchange reaction was studied through the paramagnetic effect of the complex on the relaxation rate of the (17)O nucleus of the bulk water. In addition to variable-temperature experiments, high-pressure NMR techniques were applied to elucidate the intimate nature of the water-exchange mechanism. The water molecule in the seventh coordination site of the edta complex is strongly labilized, as shown by the water-exchange rate constant of (2.7 +/- 0.1) x 106 s(-1) at 298.2 K and ambient pressure. The activation parameters DeltaH(not equal), DeltaS(not equal), and DeltaV(not equal) were found to be 43.2 +/- 0.5 kJ mol(-1), +23 +/- 2 J K(-1) mol(-1), and +8.6 +/- 0.4 cm(3) mol(-1), respectively, in line with a dissociatively activated interchange (Id) mechanism. The scalar coupling constant (A/h) for the Fe(II)-O interaction was found to be 10.4 MHz, slightly larger than the value A/h = 9.4 MHz for this interaction in the hexa-aqua Fe(II) complex. The solution structure and dynamics of Fe(II)(edta)(H(2)O) were clarified by (1)H and (13)C NMR experiments. The complex undergoes a Delta,Lambda-isomerization process with interconversion of in-plane (IP) and out-of-plane (OP) positions. Acetate scrambling was also found in an NMR study of the corresponding NO complex, Fe(III)(edta)(NO(-)).
Fe(II)(乙二胺四乙酸)(H₂O)（乙二胺四乙酸 = ethylenediaminetetraacetate）在水溶液中的不稳定性和结构动力学强烈依赖于溶剂相互作用。为了研究溶液结构和水交换机制，应用了¹H、¹³C和¹⁷O核磁共振技术。通过该配合物对大量水中¹⁷O核弛豫速率的顺磁效应研究了水交换反应。除了变温实验外，还应用了高压核磁共振技术来阐明水交换机制的内在本质。乙二胺四乙酸配合物第七配位位点的水分子高度不稳定，在298.2 K和常压下其水交换速率常数为(2.7±0.1)×10⁶ s⁻¹。发现活化参数ΔH(≠)、ΔS(≠)和ΔV(≠)分别为43.2±0.5 kJ mol⁻¹、+23±2 J K⁻¹ mol⁻¹和+8.6±0.4 cm³ mol⁻¹，这与解离活化交换（Id）机制一致。发现Fe(II)-O相互作用的标量耦合常数(A/h)为10.4 MHz，略大于六水合Fe(II)配合物中该相互作用的值A/h = 9.4 MHz。通过¹H和¹³C核磁共振实验阐明了Fe(II)(乙二胺四乙酸)(H₂O)的溶液结构和动力学。该配合物经历了面内（IP）和面外（OP）位置相互转换的Δ,Λ-异构化过程。在相应的NO配合物Fe(III)(乙二胺四乙酸)(NO⁻)的核磁共振研究中也发现了乙酸根的重排。
