Belén Gil

Synthesis, characterization and luminescence properties of homoleptic platinum(II) acetylide complexes

A family of homoleptic tetraalkynylplatinate(II) complexes (NBu4)2[Pt(CCR)4] containing various arylsubstituted (R = C6H4X), where X is an electron-donating, -withdrawing or -delocalizing substituent, and ethynylpyridine (C5H4N-2, C5H4N-4) ligands have been prepared. The structures of complexes with R = (4-CF3)C6H4 (4·2HCCl3), (4-CN)C6H4 (6·H2O) and C5H4N-4 (9b·HCCC5H4N-4·2H2O) have been determined by single-crystal X-ray diffraction. While in the case of 4 two molecules of CHCl3 are incorporated to the anion by short CH⋯π interactions, for the para-pyridylethynyl derivative one H2O molecule connect different anions through moderate N⋯H–O–H⋯N intermolecular interactions, giving an extended one-dimensional chain. The photophysical and electrochemical properties of the complexes have been examined. All of them display emissions at 77 and 298 K in the fluid and solid state, with lifetimes in the microsecond regime. In some cases the emission profile is clearly the envelope of several closely bands, whose relative intensity depends on the excitation energy. On the basis of TD-DFT theoretical calculations on the anion [Pt{CC(4-CN)C6H4}4]2− of complex 6, it is proposed that the emissions are due to triplet intraligand excited states, with both an aryl (or pyridyl) and acetylenic character, which arise from an admixture of π → π*(CCR) IL and dπ(Pt) → π*(CCR) MLCT transitions.

Reversible Binding of Solvent to Naked PbII Centers in Unusual Homoleptic Alkynyl‐Based Pt2Pb2 Clusters

We report a series of luminescent sandwich-type clusters [Pt2 Pb2 (C≡CR)8] (R=Tol, 1; C6 H4 OMe-3, 2; C6 H4 OMe-4, 3) with a dynamic Pt2 Pb2 metallic core, which is key to their intriguing stimuli-responsive photophysical properties. The solvent-free solids 1-3 display an orange emission ascribed to charge transfer from Pt-alkynyl fragments to a delocalized orbital with mixed Pt2 Pb2 /C≡CR nature, with a predominant lead contribution and Pb⋅⋅⋅Pb bonding character ((3) MLCCT/(3) IL). They exhibit mechanical, color, and luminescence changes that are reversible and perceivable with the naked eye, which are attributed to small inter- and intramolecular structural modifications induced by gentle grinding. Interestingly, 1 and 2 also exhibit remarkable and fast reversible vapochromic responses to donor solvent vapors (acetone, THFMe-2: yellow; NCMe: green, vs. dry solids: orange). The structures of 1(acetone)2 ⋅2(Me2 CO), 2(acetone)3 , and 2(THFMe-2)2 allow the vapochromic responses to be ascribed to the fast creation/disruption of solvate clusters [Pt2 Pb2 (C≡CR)8 Sx] (x≥2), with concomitant electronic and geometrical modifications within the Pt2 Pb2 core, which are easily accessible through a slight change in the stereochemical activity of the lone pair. The binding of one (or two) solvent molecules to Pb(2+) increases the Pb⋅⋅⋅Pb separation in the metallic core, causing a destabilization of the target orbital and larger energy gaps of the transitions. All the solvates exhibit remarkable rigidochromism upon a decrease in temperature, which is also associated with the gradual increase in the transannular Pb⋅⋅⋅Pb separation, as revealed by X-ray crystallography of 1(acetone)2 at different temperatures. Investigation of the crystal lattice of 1⋅CH2 Cl2 and 3⋅2 CH2 Cl2 further suggests that the lack of vapor stimuli response of complex 3 could be attributed to the presence of competitive additional secondary intermolecular Pb⋅⋅⋅O(OMe) contacts, which give rise to a more compact network built up from extended chains of clusters.

Synthesis, structural characterisation and photophysics of anionic cyclometalated bis(alkynyl)(benzo[h]quinolinate)platinate(II) species

The alkynylation of [Pt(bzq)(μ-Cl)]2 (bzqH = benzo[h]quinoline) with excess of LiCCR in diethyl ether leads to novel (7,8-benzoquinolinate)bis(alkynyl)platinate(II) monoanionic species [Pt(bzq)(CCR)2]− (R = tBu 1, SiMe32, Ph 3, Tol 4, C6H4CF3-4 5, C5H4N-2 6, C6H4–CCPh 7) which have been isolated as tetrabutylammoniun salts. The molecular X-ray structures of 3 and 6 reveal the presence of discrete anions with bond lengths and angles similar to those of related cyclometalated Pt compounds and no evidence of π–π or Pt–Pt stacking interactions. The influence of the R substituent on the photophysics of the complexes has been examined by UV-visible absorption, emission spectroscopy and cyclic voltammetry. Complexes 1–6 show a similar strong luminescence in both the solid state (structureless emission) and frozen solutions (well-resolved vibronic structures) while the emissions in solution at room temperature are red shifted (relative to the glass) and weak. For these complexes, on the basis of TD-DFT calculations which reproduce the experimental structure of anion 3, [Pt(bzq)(CCPh)2]−, the emissions are proposed to arise from mixed [π CCR/Pt d/π (bzq) → π* bzq] transitions. In contrast, complex 7 which contains the extended p-phenylethynylphenylacetylide ligand, CCC6H4–CCPh, displays a structured emission both at 298 K and in glassy CH2Cl2 solutions. In this case the lack of a significant rigidochromism and DFT theoretical calculations support the involvement of a low-lying, metal perturbed acetylenic 3ππ* (CCC6H4–CCPh) excited state.