Electrochemical, Spectral, and Computational Studies of Metalloporphyrin Dimers Formed by Cation Complexation of Crown Ether Cavities

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• 作者：Raghu Chitta ; Lisa M. Rogers ; Amber Wanklyn ; Paul A. Karr ; Pawan K. Kahol ; Melvin E. Zandler ; and Francis D'Souza
• 刊名：Inorganic Chemistry
• 出版年：2004
• 出版时间：November 1, 2004
• 年：2004
• 卷：43
• 期：22
• 页码：6969 - 6978
• 全文大小：394K
• 年卷期：v.43,no.22(November 1, 2004)
• ISSN：1520-510X

文摘

The effect on the electrochemical oxidation and reduction potentials of 5,10,15,20-tetrakis(benzo-15-crown-5)porphyrin (TCP) and its metal derivatives (MTCP; M = Mg(II), VO(IV), Co(II), Ni(II), Cu(II), Zn(II), Pd(II), Ag(II))upon potassium ion induced dimerization of the porphyrins was systematically performed in benzonitrile containing0.1 M (TBA)ClO₄ by differential pulse voltammetry technique. The HOMO-LUMO energy level diagram constructedfrom the electrochemical data revealed destabilization of the HOMO level and stabilization of the LUMO level upondimer formation while such a perturbation was larger for the HOMO level than the LUMO level. The geometry andelectronic structure of a representative ZnTCP and its dimer, K₄(ZnTCP)₂, were evaluated by the ab initio B3LYPmethod utilizing a mixed basis set of 3-21G(*) for Zn, K, O, and N and STO-3G for C and H. The inter-porphyrinring distance of the dimer calculated from the optimized geometry agreed with the spectroscopically determinedone, and the calculated HOMO and LUMO frontier orbitals revealed delocalization on both of the porphyrins rings.The metal-metal distances calculated from the triplet ESR spectra of the K⁺ induced porphyrin dimers bearingparamagnetic metal ions in the cavity followed the trend Cu-Cu < VO-VO < Ag-Ag. However, the spectral shiftsresulting from the exciton coupling of the interacting porphyrin mages/gifchars/pi.gif" BORDER=0 >-systems revealed no specific trend with respectto the metal ion in the porphyrin cavity. Additionally, linear trends in the electrochemically measured HOMO-LUMO gap and the energy corresponding to the most intense visible band of both MTCP and K₄(MTCP)₂ wereobserved. A reduced HOMO-LUMO gap predicted for the dimer by B3LYP/(3-21G(*), STO-3G) calculations wasconfirmed by the results of optical absorption and electrochemical studies.