A 3d‐4f Complex Constructed by the Assembly of a Cationic Template, [Cu(en) 2 ] 2+ , and a 3D Anionic Coordination Polymer, [Sm 2 (C 2 O 4 ) 3 (C 5 O 5 )(H 2 O) 2 ] 2–

A three‐dimensional (3D) 3d‐4f complex, [Cu(en) 2 ][Sm 2 (C 5 O 5 )(C 2 O 4 ) 3 (H 2 O) 2 ] · 8H 2 O ( 1 ) (en = ethylenediamine, C 5 O 5 2– = dianion of 4,5‐dihydroxycyclopent‐4‐ene‐1,2,3‐trione), were prepared via the in‐situ ring‐opening oxidation reaction of croconate in the presence of the template‐directed complex, [Cu(en) 2 ] 2+ cation. The structural characterization determined by X‐ray diffraction determination reveals that the 3D anionic coordination polymer of [Sm 2 (C 2 O 4 ) 3 (C 5 O 5 )(H 2 O) 2 ] 2– in 1 can be describe in terms of in‐plane 2D honeycomb‐like [Sm 2 (C 2 O 4 ) 3 ] layered frameworks bridged by oxalate with bis ‐chelating mode, being mutually interlinked via the bridge of μ 1,2,3,4 ‐croconate ligands with bis ‐chelating coordination mode to complete the 3D open framework, which gives rise to 1D channels with pore size of 14.023 × 11.893 Å (longest atom–atom contact distances) along the b axis. The structure‐directing complex, [Cu(en) 2 ] 2+ , and solvated water molecules are resided into these honeycomb‐type hexagonal channels. The thermal stability of 1 was further studied by TGA and in‐situ powder X‐ray diffraction measurement.