Kinetic behavior of Mn(III) complexes of pyrophosphate, EDTA, and citrate
Kinetic behavior of Mn(III) complexes of pyrophosphate, EDTA, and citrate
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DOI：
10.1021/es980308e
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发表时间：
1998-10-01
影响因子：
11.4
通讯作者：
Morgan, JJ
中科院分区：
文献类型：
--
作者：
Klewicki, JK;Morgan, JJ
通过以下一般反应在溶液中快速制备 Mn3+ 离子与配体焦磷酸盐 (P2O74-)、EDTA (C10H12O8N24-、乙二胺四乙酸盐 (4-)) 或柠檬酸盐 (CIT3-、C6H5O73-) 的水配合物：Mn(VII) + 4Mn(II)L + L--> 5Mn(III)L，其中 L 是配体（已知过量）。通过预先添加所需的酸、碱或缓冲液获得复合溶液的不同初始pH值。通过适当波长下的光吸光度监测Mn(III)L络合物随时间的消失。发现每个 Mn(III)L 络合物的损失率取决于 pH 值和[配体](T)/[Mn](T) 比率。在中性pH值和类似的配体与金属比率下Mn(III)L消失的相对化学时间尺度是焦磷酸锰(III) > 柠檬酸锰(III) >> EDTA锰(III)。动力学观察被解释为反映了焦磷酸盐（一种非氧化还原活性化合物）的配体水解和歧化、从柠檬酸盐到 Mn3+ 的内球电子转移以及从 EDTA 到 Mn3+ 的外球和分子内电子转移。在 O-2 存在下，柠檬酸锰(II)络合物被再氧化为柠檬酸锰(III)。结果表明，在某些天然水条件下（例如，存在明显的氧化还原梯度或产生显着浓度的超氧化物、过氧化物和羟基自由基的情况下），具有与配体过量形成Mn(III)络合物和动力学稳定的潜力。天然水中的邻苯二酚和腐殖质等其他配体可能会出现与此处报道的类似的 Mn(III) 行为。
Aqueous complexes of Mn3+ ion with the ligands pyrophosphate (P2O74-), EDTA (C10H12O8N24-, ethylenediaminotetraacetate(4-)), or citrate (CIT3-, C6H5O73-) were prepared rapidly in solution by the general reaction: Mn(VII) + 4Mn(II)L + L--> 5Mn(III)L, where L is the ligand (in known excess). Different initial pH values of the complex solutions were obtained by prior addition of required acid, base, or buffer. Disappearance of Mn(lll)L complex with time was monitored by light absorbance at appropriate wavelengths. Rates of loss for each Mn(lll)L complex are found to depend on pH and the ratio [ligand](T)/ [Mn](T). Relative chemical time scales for Mn(lll)L disappearance at neutral pH and similar ligand-to-metal ratios were manganese(III) pyrophosphate > manganese(III) citrate >> manganese(lll) EDTA. The kinetic observations are interpreted as reflecting ligand hydrolysis and disproportionation in the case of pyrophosphate (a nonredox active compound), inner-sphere electron transfer from citrate to Mn3+, and both outer-sphere and intramolecular electron transfer from EDTA to Mn3+. In the presence of O-2, manganese(ll) citrate complex is reoxidized to manganese(III) citrate. The results suggest a potential for formation of Mn(lll) complexes with ligands in great excess and kinetic stabilization under certain natural water conditions (e.g., where pronounced redox gradients are present or where appreciable concentrations of superoxide, peroxide, and hydroxyl radical are produced). Similar Mn(III) behavior to that reported here might be anticipated for other ligands such as catechol and humic matter in natural waters.