Two Cd–Ln clusters [Ln8Cd24L12(1,4-BDC)4(OAc)38(OH)2] (Ln = Eu (1) and Nd (2)) were constructed using a flexible Schiff base and rigid 1,4-BDC ligands. The Cd–Ln clusters exhibit interesting nano-drum-like structures which allow direct visualization by TEM. The introduced 1,4-BDC units act as efficient energy transfer donors for lanthanide luminescence, resulting in superior luminescence properties of 1 and 2.

•There are few reports on the lanthanide complexes synthesized from flexible ligands. Here we design a long-chain Schiff base ligand (length, ~ 23 Å), and report the synthesis of its binuclear lanthanide complexes with nanoscale sizes (8 × 12 × 12 Å).•Compared with the NIR luminescence of some lanthanide ions commonly used to study, such as Yb(III), Nd(III) and Er(III), those of Ho(III) are less well studied. Here we report the interesting NIR luminescence properties of a binuclear Ho(III) complex.•Interestingly, we found that the triple-decker Nd(III) complex 1 shows better NIR luminescence properties than the ring-like Nd(III) complex 2, due to the fact that the central metal ions in 1 are better shielded from solvent interactions than those in 2.Three binuclear lanthanide complexes [Nd2(L1)3(MeOH)]·MeOH·H2O (1) and [Ln2(H2L2)2(OAc)4]·2(CF3SO3)·MeOH·EtOH (Ln = Nd (2) and Ho (3)) were prepared using two Schiff base ligands. Interestingly, 1 has a triple-decker structure with two lanthanide ions enclosed by three rigid conjugated Schiff base ligands (H2L1), while 2 and 3 show nanoscale ring structures (8 × 12 × 12 Å) formed by flexible long-chain Schiff base ligands (H2L2, ~ 23 Å) with the lanthanide ions located in the center. Upon excitation of the ligand-centered absorption bands, 1–2 and 3 show typical NIR emission spectra for Nd3 + and Ho3 + ions, respectively. In 1, the Nd(III) centers are shielded within the decker-like structure and surrounded by chromogenic Schiff base ligands (energy transfer donors). Luminescence studies show that the NIR emission lifetime of 1 is longer than that of 2 in solution.Three binuclear lanthanide complexes were prepared using rigid conjugated and flexible long-chain Schiff base ligands and their NIR luminescence properties were investigated.Download high-res image (104KB)Download full-size image

Two classes of Ni–Ln clusters [Ln4Ni3L3(OAc)6(NO3)3(OH)3] (Ln = Gd (1) and Tb (2)) and [Ln6Ni7L6(OAc)12(OH)6](OH)2 (Ln = Gd (3) and Dy (4)) were prepared using a specifically designed Schiff base ligand built around a flexible (CH2)2O(CH2)2O(CH2)2 chain. 1 and 2 exhibit cone-like structures, while 3 and 4 have nanosized sandwich architectures. The structures were studied by single-crystal X-ray diffraction and TEM, and magnetic properties were investigated.

The synthesis, crystal structures and photophysical properties of thirty-one 4f and d-4f polynuclear complexes and coordination polymers based on nine flexible salen-type ligands are described in this review. Most of these lanthanide complexes exhibit either interesting “twisted”, drum-like or polymeric structures. In these complexes, the multidentate salen-type ligands can efficiently sensitize lanthanide emissions by serving as antennas that absorb excitation light and transfer the energy to the lanthanide centers. With the lanthanide ions encapsulated by chromophoric salen-type ligands and shielded from solvent molecules which can quench the emissions from lanthanide ions, those lanthanide complexes which have “twisted” and drum-like structures show impressive luminescence properties.The synthesis, crystal structures and photophysical properties of thirty-one 4f and d-4f polynuclear complexes and coordination polymers based on nine flexible salen-type ligands are described in this review. The multidentate salen-type ligands can efficiently sensitize lanthanide emissions by serving as antennas that absorb excitation light and transfer the energy to the lanthanide centers.

Reactions of H2salen (H2L, N,N′-ethylene bis(salicylideneimine)) with Yb(CF3SO3)3, Yb(OAc)3·4H2O and Yb(NO3)3·6H2O in MeOH–EtOH under reflux gave NIR luminescent complexes [Yb6L9(H2L)2] (1), [Yb3L3(HL)(OH)2] (2) and [Yb2L2(H2L)2(NO3)(MeOH)2]·NO3 (3), respectively.

Reactions of H2salen (H2L, N,N′-ethylene bis(salicylideneimine)) with Yb(CF3SO3)3, Yb(OAc)3·4H2O and Yb(NO3)3·6H2O in MeOH–EtOH under reflux gave NIR luminescent complexes [Yb6L9(H2L)2] (1), [Yb3L3(HL)(OH)2] (2) and [Yb2L2(H2L)2(NO3)(MeOH)2]·NO3 (3), respectively.

Two classes of Ni–Ln clusters [Ln4Ni3L3(OAc)6(NO3)3(OH)3] (Ln = Gd (1) and Tb (2)) and [Ln6Ni7L6(OAc)12(OH)6](OH)2 (Ln = Gd (3) and Dy (4)) were prepared using a specifically designed Schiff base ligand built around a flexible (CH2)2O(CH2)2O(CH2)2 chain. 1 and 2 exhibit cone-like structures, while 3 and 4 have nanosized sandwich architectures. The structures were studied by single-crystal X-ray diffraction and TEM, and magnetic properties were investigated.