Three-component coordination networks based on [Ru(phen)(CN)4]2- anions, near-infrared luminescent lanthanide(III) cations, and ancillary oligopyridine ligands:: structures and photophysical properties

A series of cyanide-bridged coordination networks has been prepared which contain [Ru(phen)(CN)(4)](2-) anions, Ln(III) cations, and additional oligopyridine ligands (1,10-phenanthroline, 2,2':6',2(m)-terpyridine or 2,2'-bipyrimidine) which coordinate to the Ln(m) centres. Five structural types have been identified and examples of each type of structure are described: these are hexanuclear Ru(4)Ln(2) clusters; two-dimensional Ru-Ln sheets with a honeycomb pattern of edge-linked Ru(6)Ln(6) hexagons; one-dimensional chains consisting of two parallel cross-linked strands in a ladder-like arrangement; simple single-stranded chains of alternating Ru/Ln components; and a one-dimensional 'chain of squares' in which Ru(2)Ln(2), squares are linked by bipyrimidine bridging ligands which connect to the Ln(III) corners of adjacent squares in the sequence. The (MLCT)-M-3 luminescence characteristic of the [Ru(phen)(CN)(4)](2-) units is quenched in those networks containing Ln(III) which have low-lying near-infrared luminescent f-f states [Pr(III), Nd(III), Er(III), Yb(III)], with sensitised Ln(III)-based near-IR luminescence generated by d -> f energy-transfer. The rate of d -> f energy-transfer, and hence the degree of quenching of the (MLCT)-M-3 luminescence from the [Ru(phen)(CN)(4)](2-) units, depends on the availability of f-f levels of an appropriate energy on the Ln(III) centre, with Nd(m) (with a high density of low-lying f-f states) being the most effective energy-acceptor and Yb(III) (with a single low-lying f-f states) being the least effective. Rates of d -> f energy-transfer to different Ln(III) centres could be determined from both the residual (partially quenched) lifetimes of the (MLCT)-M-3 luminescence, and-in the case of the Yb(III) networks-by a rise-time for the sensitised near-IR luminescence. The presence of the 'blocking' polypyridyl ligands, which reduced the number of cyanide and water ligands that would otherwise coordinate to the Ln(III) centres, resulted in increases in the Ln(III)-based emission lifetimes compared to networks where these blocking ligands were not used.