New hetero-dilanthanide complexes containing Ln1(fod)3 and Ln2(fod)3 fragments (Ln=Pr–Nd; Nd–Sm; Eu–Tb and Ho–Er) linked by bis-diimine bridging ligand

New hetero-dilanthanide β-diketonate complexes of the type [Ln1Ln2(fod)6(μ-bpm)] {fod is the anion of 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione; bpm = 2,2′-bipyrimidine; Ln1 = Pr and Ln2 = Nd (1); Ln1 = Nd and Ln2 = Sm (2); Ln1 = Eu and Ln2 = Tb (3) and Ln1 = Ho and Ln2 = Er (4)} have been isolated by reacting sequentially, the coordinatively unsaturated Ln(fod)3 chelates of two different lanthanides and 2,2′-bipyrimidine bridging ligand in 1:1:1 molar ratio, in ethanol. The purity and hetero-dilanthanide nature of the complexes has been confirmed by NMR, 4f–4f absorption spectroscopies and electrospray mass spectrometry. The oscillator strength of the hypersensitive transitions confirms the presence of the two different lanthanides in the complexes in 1:1 ratio. The complexes 2 and 3 display strong pink and red luminescences, respectively. The intramolecular Tb(III) → Eu(III) energy transfer has been observed in complex 3.