PHTHALOCYANINE CHEMISTRY
ABPL has been active in Phthalocyanine chemistry for over 30 years. Current interest reflects the high redox activity and stability of these species in the design of chemical sensors. Langmuir Blodgett films (LB), or monomolecular films adsorbed onto highly oriented or basal plane graphite are studied [1]. The electrochemical and electrocatalytic activity of these films are studied in depth. Current targets include hydrogen sulfide, oxygen, nitrous oxide, carbon monoxide, carbon dioxide, hydrazine, hydroxylamine, etc. Langmuir films are also studied in-situ on a trough to explore their chemical reactivity as a pre-requisite for studying transferred films [2]. Recently we have studied dinuclear ruthenium phthalocyanine [3] and X16PcRu species (X = Cl, F) [4] and a range of cationic species [5,6]. These cationic species are of great interest since they display concerted two-electron redox processes; studies re in hand to couple these to multi-electron electrocatalysis. The design of metallophthalocyanine species with specific redox properties is being studied in the context of Hammett and Ligand Electrochemical Parameters (see below)
NON-INNOCENT LIGANDS
ABPL has also been interested for some 20 years in the electrochemistry, spectroscopy and electronic structural aspects of ligands which can exist in several oxidation states. These include quinones, aminophenols, quinonediimines (e.g. especially 1,2-o-benzoquinonediimine (bqdi)) and their sulfur analogs [e.g. 7-11]. These species, usually as their ruthenium complexes, exist in a redox series whose members can be explored electrochemically and spectro-electrochemically. The electronic structure is then evaluated as a function of the net number of electrons involved. The methodology has been developed in a general fashion for any complex, to link electrochemical properties to the optical properties of a molecule, e.g. see recent review [12]. More recent synthetic work has focussed on polyfunctional ligands such as 1,2-dihydroxy- and 1,2-diaminoanthraquinone, and 3,3',4,4'-tetraimino- 3,3',4,4'-tetrahydrobiphenyl. Techniques used to explore these electronic aspects also include resonance Raman, Electron and Nuclear Magnetic Resonance and FTIR spectroscopy. The assignments of the electronic structure and rich electronic spectra displayed by these systems is facilitated by close analysis of their electrochemical properties, and by the use of computational methods, especially Density Functional Theory (DFT) and INDO/s (ZINDO)[13-17].The complex [Ru(NH3)2Cl2(bqdi)] is a recent example that shows an astonishingly high degree of pi-back donation [18]
ELECTROCHEMICAL PARAMETERS
ABPL has introduced the Ligand Electrochemical Series [19] whose parameters, EL(L), used in an additive fashion, can predict the electrochemical redox potentials for a wide range of metal couples, and some ligand reduction couples in coordination chemistry and organometallic chemistry. Recently the Series has also been extended to include organometallic sandwich species [20]. The fundamental significance of these parameters, which are ligand but not metal dependent, is also being explored in terms of the sigma and pi characteristics of the ligand binding function [21]. This theory has recently been reviewed [22]
References
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[2] Y. Fu, K. Jayaraj and A.B.P. Lever, Langmuir, 10, 3836-41, (1994); Y. Fu and A.B.P. Lever, J.Phys.Chem., 95, 6979-84 (1991).
[3] M. Ebadi, C. Alexiou, and A. B. P. Lever Can. J. Chem. 79, 992-1001 (2001)
[4] D.Christendat, S. Morin, A. B. P. Lever et al., paper in preparation (2005).
[5] J. Chen, A. B. P. Lever, B . M. Hoffman et al, paper in preparation
[6] The Surface Electrochemistry of Metallophthalocyanines, Dioxygen Reduction
A.B.P. Lever and Y. Ma
"New Trends in Molecular Electrochemistry, Edited by A. J. L. Pombeiro and C. Amatore, Fontismedia (and Marcel Dekker), Lausanne, Switzerland 99-126 (2004)
[7] H. Masui, P.R. Auburn and A.B.P. Lever, Inorg.Chem., 30,2402-10 (1991);
[8] A. Del Medico, E.S. Dodsworth, P.R. Auburn, W.J. Pietro and A.B.P.Lever, Inorg.Chem., 33, 1583-4 (1994).
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[10] M. Ebadi and A. B. P. Lever, Inorg. Chem. 38,467-474, (1999)
[11] A. DelMedico , E. S. Dodsworth, A. B. P. Lever and W. J. Pietro, Inorg. Chem. 43, 2654-2671 (2004)
[12] S.I. Gorelsky and A.B.P. Lever, J. Organomet. Chem 635, 187-196 (2001)
[13] Electrochemistry, Charge Transfer Spectroscopy and Electronic Structure A. B. P. Lever and E. S. Dodsworth, in "Inorganic Electronic Structure and Spectroscopy", Ed. E. I. Solomon and A. B. P. Lever, John Wiley and Sons, New York, 1999, Vol. 2, 227-287
[14] S. I. Gorelsky, A. B. P. Lever, and M. Ebadi Coord. Chem. Rev., 230, 97-105 (2002)
[15] S. I. Gorelsky and A. B. P. Lever Can. J. Appl. Spectry, 48, 93- 105 (2003)
[16] S. I. Gorelsky, E. S. Dodsworth, A. B. P. Lever,and Anton A. Vlcek, Coord. Chem. Rev.174, 469-496(1998).
[17] S. I. Gorelsky, and A. B. P. Lever, Struct. Bonding 107, 77-114 (2004).
[18] J. Rusanova, E. Rusanov, A.B.P. Lever,et al paper in preparation (2005)
[19] A.B.P. Lever, Inorg.Chem., 29, 1271-1285, (1990).
[20] S. Lu, V. V. Strelets, M. F. Ryan, W. J. Pietro and A. B. P. Lever, Inorg.Chem., 35, 1013-23 (1996)
[21] S. S. Fielder, M. C. Osborne, A. B. P. Lever and W.J. Pietro, J.Am. Chem. Soc. 117, 6990 (1995)
[22] A. B. P. Lever and E. S. Dodsworth, in Comprehensive Coordination Chemistry, II, Vol. 2 Edited by A. B. P. Lever, Elsevier Publishers, 2004