The effects of point of substitution on the electrochemical behavior of new manganese phthalocyanines, tetra-substituted with diethylaminoethanethiol Isaac Adebayo Akinbulu, Tebello Nyokong * Department of Chemistry, Rhodes University, Grahamstown 6140, South Africa article info Article history: Received 4 September 2009 Received in revised form 21 January 2010 Accepted 4 June 2010 Available online 17 June 2010 Keywords: Manganese Diethylaminoethanethiol Phthalocyanine Cyclic voltammetry Spectroelectrochemisrty abstract The syntheses and comparative studies of the spectral, voltammetry and spectroelectrochemical proper- ties of new manganese phthalocyanine complexes, tetra-substituted with diethylaminoethanethio at the peripheral (complex 3a) and non-peripheral positions (complex 3b) are reported. Solution electrochem- istry of complex 3a showed quasi-reversible metal-based (Mn III Pc 2 /Mn II Pc 2 , E 1/2 = 0.07 V vs. Ag|AgCl) and ring-based (Mn II Pc 2 /Mn II Pc 3 , E 1/2 = 0.78 V vs. Ag|AgCl) reductions, but no ring-based oxidation. However, complex 3b showed weak irreversible ring-oxidation signal (E p = +0.86 vs. Ag|AgCl). Reversible metal-based (Mn III Pc 2 /Mn II Pc 2 , E 1/2 = 0.04 V vs. Ag|AgCl) and ring-based (Mn II Pc 2 /Mn II Pc 3 , E 1/2 = 0.68 V vs. Ag|AgCl) reductions were also observed for complex 3b. Spectroelectrochemistry was used to confirm these processes. Reduction process involving the metal (Mn III Pc 2 /Mn II Pc 2 ) was associated with the formation of manganese l-oxo complex in complex 3a. Ó 2010 Elsevier B.V. All rights reserved. 1. Introduction The present and potential applications of metallophthalocya- nine (MPc) complexes have attracted unprecedented research interest in these macrocycles. Their uses in electronic devices, as gas sensors, as photosensitizers, in non-linear optics, in electro- chromic devices and in Langmuir–Blodgett films have been reported [1,2]. Incorporation of different metals into the phthalo- cyanine cavity and changes in the nature and position of substitu- ent (peripheral and non-peripheral), give MPc complexes with different chemical, physical, electrochemical, spectroscopic, elec- trocatalytic, photophysical and photocatalytic properties. The pos- sibility of tuning these properties, to form MPc complexes with specific requirements, needed for different applications, promotes the versatility of these macrocycles. The electrochemical properties of manganese phthalocyanine (MnPc) complexes have attracted attention [3–5]. MnPc complexes show interesting electrochemical behavior with oxidation states of the central Mn ion ranging from Mn I to Mn IV [6–16]. Mn IV Pc spe- cies rarely occurs, but has been reported recently [11,12]. The reduction of Mn II Pc 2 species has been extensively contested, with some authors proposing metal reduction to Mn I Pc 2 species and others ring reduction forming Mn II Pc 3 species. The latter was ob- served in this work. The formation of l-oxo complex in DMF and in the presence of oxygen is common for MnPc complexes, hence in this work the effects of changing the substituent position on the formation of l-oxo MnPc species is discussed. In the present work, we report on the syntheses and the ef- fects of the point of substitution on the spectral, voltammetric and spectroelectrochemical properties of new MnPc complexes containing diethylaminoethanethio, tetra-substituted at the peripheral (complex 3a) and non-peripheral (complex 3b) posi- tions (Scheme 1). The electrochemical behavior of complexes 3a and 3b is compared with that of the octa-substituted deriva- tives {manganese(III) (acetate) octakis-(2-diethylaminoethanethi- o) phthalocyanine, OAcMnODEAETPc(b)}, reported before [17]. The formation of different redox products is highly influenced by the nature of substituents in MnPc complexes [18]; hence it is important to increase the range of substituted MnPc complexes. The choice of the substituent employed in this work (diethy- laminoethanethio) is influenced by the possibility of forming poly- mers and self-assembled monolayers of the complexes on suitable electrodes, thus promoting their uses as electrocatalysts and in the fabrication of electrochemical sensors. The nitrogen group in the substituent is oxidizable, hence can generate radicals necessary for initiating polymer formation [19–22]. MPc complexes containing diethylaminoethanethio on periph- eral positions (either tetra- or octa-substituted) have been re- ported in the literature [23–27]. The central metals which have been employed in the literature include Ni(II), Zn(II) or Co(II). 0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2010.06.003 * Corresponding author. Tel.: +27 46 6038260; fax: +27 46 6225109. E-mail address: t.nyokong@ru.ac.za (T. Nyokong). Inorganica Chimica Acta 363 (2010) 3229–3237 Contents lists available at ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica