Electrochemistry of metal phthalocyanines in organic solvents at variable pressure.
Electrochemistry of metal phthalocyanines in organic solvents at variable pressure.
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DOI：
10.1021/ic040032d
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发表时间：
2004-06
影响因子：
4.6
通讯作者：
Bazhang Yu;A. Lever;T. Swaddle
中科院分区：
文献类型：
--
作者：
Bazhang Yu;A. Lever;T. Swaddle
报道了具有代表性的金属酞菁在溶液中的高压电化学研究。所选择的体系是在几种供体溶剂中的ZnPc、CoPc、FePc和CoTNPc(Pc=酞菁，TNPc=四环戊氧基酞菁)和(对于CoTNPc)二氯苯，以[Bu(4)N][ClO(4)]为支持电解质，传统的铂电极为Ag(+)(CH(3)CN)/Ag。CoTNPc和ZnPc的电极反应体积DeltaV(Cell)表明，根据Drude-Nernst理论，连续的环还原导致溶剂的电致伸缩逐渐增加。然而，CoTNPc和CoPc中金属中心的还原导致的DeltaV(Cell)负值比通过类比相同电荷类型的环还原所预期的要小得多。这是由于在从Co(III)到低自旋Co(II)再到Co(I)的过程中插入反键3D(Z)2电子后轴向配体的损失。在同一脉络中，由于Franck-Condon限制，Co(III)中心还原为Co(II)的速率常数比其他金属中心或酞菁环还原的速率常数慢一个数量级。对于所有的电极反应，活化体积deltaV(El)总是为正的，并且在大多数情况下大致等于反应物扩散的活化体积deltaV(Diff)()，这表明主要的速率控制是由溶剂动力学而不是过渡态理论的活化方式控制的，对于过渡态理论来说，deltaV(El)值应该为负值。对于CoTNPc和CoPc在给体溶剂中，DeltaV(Cell)和DeltaV(El)数据与Nigin等人对CoTNPc在DMF中的连续还原步骤的指认是一致的。(Inorg.化学。1987、26、570)。
High-pressure electrochemical investigations of representative metallophthalocyanines in solution are reported. The selected systems were ZnPc, CoPc, FePc, and CoTNPc (Pc = phthalocyanine, TNPc = tetraneopentoxyphthalocyanine) in several donor solvents and (for CoTNPc) dichlorobenzene, with [Bu(4)N][ClO(4)] as supporting electrolyte and a conventional Pt electrode referred to Ag(+)(CH(3)CN)/Ag. Electrode reaction volumes deltaV(cell) for CoTNPc and ZnPc show that consecutive ring reductions result in progressive increases in electrostriction of solvent in accordance with Drude-Nernst theory. Reductions of the metal center in CoTNPc and CoPc, however, result in much less negative values of deltaV(cell) than would be expected by analogy with ring reductions of the same charge type. This is attributable to loss of axial ligands following the insertion of antibonding 3d(z)2 electrons on going from Co(III) to low-spin Co(II) and then Co(I). In the same vein, rate constants for reduction of Co(III) centers to Co(II) were an order of magnitude slower than those for other metal center or phthalocyanine ring reductions because of Franck-Condon restrictions. The volumes of activation deltaV(el) were invariably positive for all the electrode reactions and in most cases were roughly equal to the volumes of activation for reactant diffusion deltaV(diff)(), indicating predominant rate control by solvent dynamics rather than by activation in the manner of transition-state theory for which negative deltaV(el) values are expected. For CoTNPc and CoPc in donor solvents, the deltaV(cell) and deltaV(el) data are consistent with the assignments of the successive reduction steps made for CoTNPc in DMF by Nevin et al. (Inorg. Chem. 1987, 26, 570).