Title: Anion Dependent Self-Assembly of NIR Luminescent 24- and 32-metal Cd-Ln Complexes with Drum-like Architectures.
The design and construction of high-nuclearity heterometallic d-f clusters has received extensive attention due to the remarkable physical and chemical properties associated with this class of materials. Recently, research on polynuclear lanthanide complexes of Yb(III), Nd(III) and Er(III) with near-infrared (NIR) emission in the 900-1600 nm range has become a hot topic due to potential applications in bioassays and laser systems. For example, light-absorbing d-block metal chromophores (i.e. PtII,3c,d RuII,3e,f ZnII,3g,h CrII,3i,j and CdII 3k,l) can be used as sensitizers for NIR luminescence from Ln(III) centers following ligand→f and d→f energy-transfers. One of the challenges in this area is control over the stoichiometries and structures of high-nuclearity d-f complexes.
Flexible ligands may provide more possibilities for the construction of unique frameworks because of their freedom of conformation. Our recent studies have focused on the synthesis of polynuclear lanthanide complexes with different polydentate ligands. We report here two series of NIR luminescent 4d-4f heterometallic clusters [Ln8Cd24L12(OAc)48] and [Ln6Cd18L9Cl8(OAc)28] (H2L = N,N-bis(3-methoxysalicylidene)hexane-1,6-diamine, Ln = Nd, Yb and Er). Although numerous polynuclear d-f complexes with varying structures have been prepared using Schiff base ligands, most of them have less than ten metal atoms. To the best of our knowledge, the 32-metal Cd-Ln complexes reported here are the highest nuclearity d-f complexes with Schiff base ligands thus far reported. More importantly, these complexes exhibit novel drum-like structures with the Ln(III) centers shielded within the nanoscale structures and protected from the outside solvent molecules which can quench lanthanide luminescence. This may help to improve their NIR luminescent properties. (J. Am. Chem. Soc., 2013, 135 (23), pp 8468–8471).
