Journal of Organometallic Chemistry 637 – 639 (2001) 304 – 310 www.elsevier.com/locate/jorganchem The effect of d-block metal complexation on the spectroscopic and redox properties of ferrocene derivatives containing pyridine ligands Jonathan D. Carr a , Simon J. Coles b , M.B. Hursthouse b , James H.R. Tucker a, * a School of Chemistry, Uniersity of Exeter, Stocker Road, Exeter EX44QD, UK b Department of Chemistry, Uniersity of Southampton, Highfield, Southampton SO17 1BJ, UK Received 3 January 2001; received in revised form 16 March 2001; accepted 20 March 2001 Abstract Three ferrocene derivatives 1 – 3, each containing two pyridine ligands, form complexes with a variety of d-block metals, as evidenced by NMR and UV – vis spectroscopy and cyclic voltammetry. The X-ray crystal structures of 1 and its Mo(0) complex are reported. The Zn(II) and Cu(I) complexes of 1 – 3 have a 2/1 (ligand/metal) stoichiometry. The factors influencing the changes in the redox and chromogenic properties of these ligands upon complexation are discussed. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Ferrocene; Complexes; Sensor; Cyclic voltammetry; Spectroscopy 1. Introduction There have been numerous accounts over the past two decades of the attachment of ligand groups to ferrocene in order to assess the effect that the ferrocene has on the properties of the proximate binding site and likewise the effect that the binding site has on the properties of the ferrocene. Accordingly, ligands for transition metals [1], s-block cations [2], protons [3], p-block anions [4] and organic molecules, be they charged [5] or neutral [6], have been connected to ferrocene through covalent bonds. The ferrocene unit can affect the properties of the binding site in a number of ways. For example, redox- switched processes have been demonstrated where oxi- dation of the ferrocene either decreases [2c] or increases [6] the ligand binding affinity for a substrate. Fer- rocenes are also known to quench metal-centred lu- minescence [7], and can be used as flexible inorganic spacer units for the assembly of novel heteronuclear complexes [8]. As implied by the redox-switched processes described above, it is well known that binding at a proximate site can affect the oxidation potential of the ferrocene unit [1–6]. In general, metal centres increase the redox po- tential by withdrawing electron density away from the ferrocene centre, whereas p-block anions and those neutral hydrogen bonding species reported so far, de- crease the potential. This aspect has attracted interest from researchers interested in developing redox-active sensors for a variety of species [9]; i.e. attaching a ferrocene group to a ligand enables the binding event to be read-out using electrochemical methods. Binding at a proximate site can also affect the UV–vis properties of the ferrocene unit [3a,10]; in general, metal complex- ation or protonation induces bathochromic shifts in the lowest energy spin-allowed ferrocene band, which ab- sorbs between 400 and 500 nm. Perhaps the most studied ferrocene-containing lig- ands have been those containing N-donor atoms, in particular pyridine and its derivatives [1a,1b]. As would be expected, the usual species bound by ferrocene-con- taining pyridyl ligands are the transition metals, al- though s-block cations have been bound by such derivatives in the presence of other hard donor atoms [11] and neutral organic molecules have been bound * Corresponding author. Fax: +44-1392-263-434. E-mail address: j.h.r.tucker@exeter.ac.uk (J.H.R. Tucker). 0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0022-328X(01)00924-X