New lanthanide metalloligands and their use for the assembly of Ln-Ag bimetallic coordination frameworks : stepwise modular synthesis, structural characterization, and optical properties

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 synthetized, 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 ( 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.