New Lanthanide Metalloligands and Their Use for the Assembly of Ln–Ag Bimetallic Coordination Frameworks: Stepwise Modular Synthesis, Structural Characterization, and Optical Properties

• Published in: Crystal growth & design 2019-09, Vol.19 (9), p.5376-5389
• Main Authors: Visconti, Marco, Maggini, Simona, Ciani, Gianfranco, Mercandelli, Pierluigi, Del Secco, Benedetta, Prodi, Luca, Sgarzi, Massimo, Zaccheroni, Nelsi, Carlucci, Lucia
• Format: Article
• Language: English
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/acs.cgd.9b00894

Stepwise self-assembly processes using new lanthanide metalloligands (Ln–MLs) and silver salts have been successfully applied to isolate 4f–4d heterometallic coordination networks of four different structural types. In particular, the new lanthanide tetrakis–chelate complexes NEt4[Ln­(L1)4] [HL1 = 1,3-bis­(4′-cyanophenyl)-1,3-propanedione; Ln = Eu (1a), La (1b), Nd (1c), Tb (1d)] and NEt4[Ln­(L2)4] (HL2 = 1,3-bis­(4′-pyridyl)-1,3-propanedione; Ln = Eu (1e), Nd (1f)] have been synthesized, characterized, and reacted with different silver salts. The use of NEt4[Ln­(L1)4] allowed then to isolate and characterize i) neutral one-dimensional ladder-like species of formula [Ln­(L1)4Ag] [Ln = Eu (2a), La­(2b), Nd­(2c), Tb­(2d)] and ii) their supramolecular isomers [Ln­(L1)4Ag] [Ln = Eu (3a), La (3b), Nd (3c), Tb (3d)] showing a very unstable 2D network structure, iii) the cationic 2D species [Ln­(L1)4Ag2]­X [Ln = Eu, X = PF6 −, CF3SO3 −, ClO4 − (4a–4c); Ln = Tb, Nd, La X = PF6 − (4d–4f)], and, only for lanthanum, iv) a fourth 2D species of formula [La­(L1)4(H2O)­Ag] (5) and sql topology. Of the eight nitrile groups on the MLs potentially coordinating, only a partial number is used for networking with Ag­(I), that is, only two in families 2 and 3 and four in family 4 and in network 5. Finally, the four structural types are rationalized in terms of a new “pincer-like” secondary building unit (SBU) consisting of a silver cation coordinating two central carbon atoms (γ carbon) of two different diketonate ligands on the same ML. Therefore, it is shown that compounds 5, 4, and 2–3 contain, respectively, none, one, or two of such pincer-like SBUs. The luminescence properties of the Ln–MLs and some of their polymeric species have been also investigated in solution and in the solid state.