Self-Assembly of Luminescent Alkynyl-Based Platinum-Cadmium Complexes Containing Auxiliary Diimine or Terpyridine Ligands.

Résumé

Reaction of different "Cd(N-N)2 2+" (N-N = bpy, dmbpy, phen) or "Cd(trpy)2+" fragments with cis- or trans-(5) dianionic bis(alkynyl)platinate substrates [Pt(C6F 5)2(C=CR)2]2- (R = Ph a, Tol b) leads to the generation of novel bimetallic neutral Platinum-Cadmium derivatives, which show photoluminescence (PL) strongly influenced by the structure and the media. In complexes [cis-Pt(C6F5) 2(C=CR)2Cd(N-N)2] (N-N = bpy (1), dmbpy (2), phen (3), the dianionic cis-bis (alkynyl)platinate fragment interacts with the "Cd(N-N)2 unit mainly through both the Cα atoms (d(Cd-Cα) = 2.417 (5) -2.554 (5) Å) and the Pt center (d(Pt-Cd) ∼3.10 Å); while in complexes [cis-Pt(C6F 5)2(C=CR)2Cd(trpy)] (4), probably because of the presence of only three Cd-N bonds, the Pt-Cd interaction is enhanced (d(Pt-Cd) ∼3.00 Å), the Cd(11) atom being additionally solvated with acetone or H2O. By contrast, in complexes [trans-Pt-(C 6F5)2(C≡CR)2Cd(bpy) 2] (6) the Cd center is found to be in a distorted trigonal-bipyramid coordination, interacting with one of the Pt-Cα bonds of the platina-bis(alkynyl) unit with very short Cd-Cα (2.376 (10) Å) and Pt-Cd (2.8931 (6) Å) bond distances. Bimetallic complexes 1-4, having cis-configured platinum fragments, exhibit, in solid state, blue and/or green phosphorescence with contribution of close emissive states of different natures: metal (Pt, Cd) perturbed ππ* intraligand (alkynyl, polyimine) manifolds mixed, to a greater (trpy complexes 4) or lesser extent, with (Pt-Cd) charge transfer (MM'CT). In glassy state (2-MeTHF, 77 K), complexes 1b-4b exhibit structured emissions mainly ascribed to (diimine 1b-3b, trpy 4b) 3ππ phosphorescence, likely mixed with some ligand (alkyne) to ligand (imine) charge transfer (3LL'CT). Complexes 6 are not emissive in solid state at room temperature. At 77 K they display a high energy 3IL/3MLCT (L = C≡CR) blue-shifted emission relative to 5 and, in the case of 6b, an additional low energy feature, tentatively ascribed to ππ stacking interactions, in accordance with the presence of very short π ··· π contacts (3.25 Å) found in the extended lattice of 6b. © 2009 American Chemical Society.