Oligomeric Metal Complexes

Abstract

Transition metal centres offer an obvious way for the introduction of charge centres or charge-carrying centres into new materials. The coordination of metal centres to ligands containing two or more distinct metal-binding domains provides a phenomenological and methodological approach to the assembly of designed novel materials. The limitations of this approach are currently being probed, and this chapter will provide an overview of the area. The emphasis will be upon synthesis rather than the properties of the materials and, in particular, the controlled assembly of materials of known nuclearity and topology.In order to keep this chapter to a reasonable length, the coverage will be restricted in a number of ways. Firstly, materials which are 'truly' polymeric will only be discussed if there are good solid state structural data to support their formulation and structural integrity. Secondly, the emphasis will be placed upon systems in which the ligand predisposes the assembly towards a particular structure. This latter restriction means that little will be said about halide. oxy and hydroxy bridged systems. Furthermore, it will be assumed for the most part that the ligands involved play some r61e in the electronic communication between metal centres and 'insulating' spacers will not be discussed in detail. In particular, the design of extended molecular materials will be discussed.The methods adopted involve the use of bridging ligands containing two or more metal-binding domains. A metal-binding domain is usually readily recognized as a conventional ligand type (for example, a phosphine, carboxylate, thiolate or oligopyridine). The linking together of the domains utilises conventional organic synthetic methods. In an ideal case, simply mixing the bridging ligand with an appropriate metal source, usually, but not necessarily in homogeneous solution, results in the formation of the desired oligomeric system. This process is shown in Fig. 1 [l].It is immediately apparent that a number of features need to be carefully controlled if the desired assembly process is to occur.The stability of the desired assembly must be maximised in order to drive the system towards the correct (i.e. wanted) product. The simplest way to achieve this is by the use of multidentate chelating ligands rather than monodentate donors. For this reason, systems based upon chloride, oxy or hydroxy bridges are not covered in detail in this article, because, although they possess extremely interesting properties, it is not usually possible, n priori, to predict exactly what material, morphology and topology will be obtained.The metal-binding domain can be tailored to the desired metal centre. This may be at a gross structural level by simply matching up the number of donor atoms to

Synthesis, Crystal Structure, and Redox and Photophysical Properties of Novel Bisphosphinoaryl RuII-Terpyridine Complexes

“…The Ru−N bonds lengths (Ru1−N1 = 2.083(2) Å; Ru1−N2 = 2.0090(19) Å; Ru1−N3 = 2.078(2) Å) are similar to those found for other Ru II complexes containing terdentate tpy ligands. 1g, As observed for other Ru II complexes containing tpy ligands, the Ru−N contacts to the central ring of the tpy ligand are shorter than those to the terminal rings. The tpy ligand is approximately planar, with torsion angles between the terminal rings and the directly bonded rings being 4.0(3)° and −3.5(3)°.…”

“…The absorption spectra of 3 , 11 , and 12 , measured in CH 3 CN at room temperature (Figure ), show features that can be easily interpreted by comparison with literature data. ,6a Table shows the absorption maxima, λ max , and the molar extinction coefficient, ε max , values for all the complexes in their +2 oxidation state. The spectra exhibit intense spin-allowed ligand-centered (LC) π → π* transitions in the UV region and broad spin-allowed d(π) → π* metal-to-ligand charge transfer (MLCT) absorption bands in the visible region.…”

“…These results are in good agreement with the more positive Ru II /Ru III redox potential values observed in the cyclic voltammetry studies, and a relationship between electrochemical redox potentials and the energy of the absorption maxima may be found. Assuming that the π(t 2g ) metal orbital and the π* orbital, involved in the first oxidation and in the first reduction processes, respectively, are also the orbitals involved in the MLCT absorption process, a linear correlation between the absorption maximum energy with increasing Δ E 1/2 (= e [ E 1/ 2 (ox) − E 1/2 (red)]) is expected 1h. The observed trend for complexes 3 , 11 , and 12 , which shows an increase in the absorption maximum energy with increasing Δ E 1/2 , is in accordance with the data previously reported for other Ru II -polypyridine complexes 1h…”

“…For the past decade, monomeric ruthenium polypyridine complexes have been widely used as efficient photosensitizers in covalently linked multicomponent systems due to their chemical stability, redox properties, and excited state reactivity . The most common polypyridyl ligands employed as terminal ligands in such species are 2,2‘-bipyridine (bpy) and 2,2‘:6‘,2‘ ‘-terpyridine (tpy).…”

A route to hierarchical materials based on complexes of metallosupramolecular polyelectrolytes and amphiphiles

“…Metal-ion-directed self-assembly is of particular interest for the construction of functional devices (10). Metal ions possess a range of well defined coordination geometries and diverse properties that are relevant in electronic and photonic materials (11).…”