Heteronuclear bipyrimidine-bridged Ru–Ln and Os–Ln dyads: low-energy 3MLCT states as energy-donors to Yb(iii) and Nd(iii)

Abstract

The complexes [Ru(^tBu₂bipy)(bpym)X₂] (X = Cl, NCS) and [M(^tBu₂bipy)₂(bpym)][PF₆]₂ (M = Ru, Os) all have a low-energy LUMO arising from the presence of a 2,2′-bipyrimidine ligand, and consequently have lower-energy ¹MLCT and ³MLCT states than analogous complexes of bipyridine. The vacant site of the bpym ligand provides a site at which {Ln(diketonate)₃} units can bind to afford bipyrimidine-bridged dinuclear Ru–Ln and Os–Ln dyads; four such complexes have been structurally characterised. UV/Vis and luminescence spectroscopic studies show that binding of the Ln(III) fragment at the second site of the bpym ligand reduces the ³MLCT energy of the Ru or Os fragment still further. The result is that in the dyads [Ru(^tBu₂bipy)X₂(µ-bpym)Ln(diketonate)₃] (X = Cl, NCS) and [Os(^tBu₂bipy)₂(µ-bpym)Ln(diketonate)₃][PF₆]₂ the ³MLCT is too low to sensitise the luminescent f-f states of Nd(III) and Yb(III), but in [Ru(^tBu₂bipy)₂(µ-bpym)Ln(diketonate)₃][PF₆]₂ the ³MLCT energy of 13 500 cm⁻¹ permits energy transfer to Yb(III) and Nd(III) resulting in sensitised near-infrared luminescence on the microsecond timescale.