Inorganic Chemistry, Vol.48, No.12, 5250-5262, 2009
Self-Assembly of Luminescent Alkynyl-Based Platinum-Cadmium Complexes Containing Auxiliary Diimine or Terpyridine Ligands
Reaction of different "Cd(N-N)(2)(2+n), (N-N = bpy, dmby, phen) or "Cd(trpy)(2+") fragments with cis- or trans- (5) dianionic bis(alkynyl)platinate substrates [Pt(C6F5)(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)(2)Cd(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)(+2n) unit mainly through both the C-alpha atoms (d(Cd-C-alpha) = 2.417 (5)-2.554(5) angstrom) and the Pt center (d(Pt-Cd) similar to 3.10 angstrom); while in complexes [cis-Pt(C6F5)(2)(C CR)(2)Cd(trpy)] (4), probably because of the presence of only three Cd-N bonds, the Pt-Cd interaction is enhanced (d(Pt-Cd) similar to 3.00 angstrom), the Cd(II) atom being additionally solvated with acetone or H2O. By contrast, in complexes [trans-Pt-(C6F5)(2)(C CR)(2)Cd(bpy)(2)] (6) the Cd center is found to be in a distorted trigonal-bipyramid coordination, interacting with one of the Pt-C-alpha bonds of the platina-bis(alkynyl) unit with very short Cd-C-alpha (2.376(10) angstrom) and Pt-Cd (2.8931 (6) angstrom) 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 pi pi* 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) (3)pi pi 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 (IL)-I-3/(MLCT)-M-3 (L = C CR) blue-shifted emission relative to 5 and, in the case of 6b, an additional low energy feature, tentatively ascribed to pi pi stacking interactions, in accordance with the presence of very short pi center dot center dot center dot pi contacts (3.25 angstrom) found in the extended lattice of 6b.