Discrete Heterotrimetallic Assemblies Based on Rod-Shaped FeII-Metalloligands and a ZnII-Porphyrin/RuII-Metallacycle.

An efficient strategy for the preparation of heterometallic discrete porphyrin assemblies, tuned both in dimensions and number of metal centers, is described. Five rod-shaped di-pyridyl FeII-metalloligands, with varied length (1.5 - 3.2 nm), lateral substituents, and number of iron centers, were used to bridge two RuII-metallacycles, made of two coplanar ZnII-porphyrin each. The resulting architectures consist of four RuII complexes, four zinc-porphyrins, and either two or four FeII-clathrochelate units. Earlier, geometrically similar sandwich-like architectures were based on purely organic connectors. Among other novel characteristics, the use of metalloligands was found to be beneficial for the overall stability, thus allowing for a solution-based characterization of the assemblies. Single crystal X-ray structures were determined for the complete collection, highlighting additional key features: the two facing ZnII-porphyrin platforms are set wide apart according to the span of the two connecting metalloligands, while the latter are parallelly aligned by the anchoring ZnII-porphyrin/RuII-metallacycles, at fixed inter Fe··Fe distance(s). Mutual control over these geometrical parameters is very strict, as evidenced by self-sorting experiments. Useful implementation of these systems into functional systems may be envisaged by pairing the peripheral metalloporphyrin photosensitizers with photo/redox/catalytically active inner metal cores.