Two- to One-Dimensional: Radii-Dependent Self-Assembly Crystal Structures and Luminescent Properties of Lanthanide Coordination Polymers with an Amide Type Semirigid Bridging Ligand

Lanthanide coordination polymers {[Ln2L3(NO3)6]·nH2O}n [Ln = Pr (1), Nd (2), Sm (3), Eu (4), Gd (5), Tb (6), Dy (7), and Er (8), where n = 0 except for 1 with n = 4 and 2 with n = 7] have been assembled using lanthanide nitrates and an amide type semirigid bridging ligand, 1,3-bis{[(2′-benzylaminoformyl)phenoxyl]methylbenzene (L), as building blocks. The crystal structures of the complexes {[Pr2L3(NO3)6]n·4H2O}n (1), {[Nd2L3(NO3)6]·7H2O}n (2), [Sm2L3(NO3)6]n (3), [Eu2L3(NO3)6]n (4), [Tb2L3(NO3)6]n (6), and [Er2L3(NO3)6]n (8)} were determined by single-crystal X-ray diffraction. Interestedly, 1 and 2 demonstrate unusual lanthanide porous noninterpenetrated honeycomb-like (6,3) topology frameworks, while 3, 4, 6, and 8 exhibit novel one-dimensional linear coordination polymeric structures. Their structural variations are attributed to lanthanide contraction effects. The luminescent properties of Sm(III), Eu(III), Tb(III), and Dy(III) complexes are also investigated in detail. The lowest triplet state (T1) energy level of this ligand matches better to the lowest resonance energy levels of Tb(III) and Dy(III) than Eu(III) and Sm(III) ions.