A Family of Three-Dimensional Lanthanide-Zinc Heterometal–Organic Frameworks from 4,5-Imidazoledicarboxylate and Oxalate

A family of lanthanide-zinc coordination polymers with two different types of three-dimensional (3-D) frameworks based on 4,5-imidazoledicarboxylic acid and oxalic acid, namely, {[Ln₂(H₂O)₂Zn₄(H₂O)₄(ImDC)₄(ox)]·6H₂O}_n (Ln = La (1), Nd (2), Sm (3), Eu (4), and H₃ImDC = 4,5-imidazoledicarboxylic acid, H₂ox = oxalic acid) and {[Ln₄(H₂O)₄Zn₄(H₂O)₄(ImDC)₄(ox)]·2CH₃OH·2H₂O}_n (Ln = Eu (4′), Gd (5), Dy (6), Ho (7), Er (8), Yb (9), and Lu (10)), were successfully constructed under certain conditions and characterized by elemental analysis, IR, thermogravimetric (TG), and single-crystal X-ray diffraction. The results reveal that compounds 1–4 (I structure) are isomorphous 3-D coordination frameworks containing two-dimensional (2-D) [Zn₂(ImDC)₂] layers and one-dimensional (1-D) Ln₂(μ₂-O)₂(ox) sine wave-like chains with 1-D square channels, while 4′–10 coordination polymers (II structure) are also isomorphous and feature 3-D pillar-layered coordination frameworks constructed from 2-D Zn-carboxylate [Zn₂(ImDC)₂] layers and Ln₂(ox) pillars with 1-D flat channels. The structural variation from I to II with the europium ion as a critical point, in which two types of europium complexes 4 and 4′ can reversibly transform into each other, may be attributed to the lanthanide contraction effect. Meanwhile, the adsorption and photoluminescent properties of the partial compounds are also investigated.