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Issue 12, 2009
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Extended structures containing Pt(II)–Tl(I) bonds. Effect of these interactions on the luminescence of cyclometalated Pt(II) compounds

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Abstract

Neutralization reactions of the appropriate precursors (NBu4)[Pt(bzq)(C[triple bond, length as m-dash]C–R)2] and (NBu4)[Pt(C⁁N)(CN)2] (C⁁N = bzq, ppy) with TlI salts afford [{PtTl(bzq)(C[triple bond, length as m-dash]C–R)2}2] [R = Ph (1), C5H4N-2 (2)] and [PtTl(C⁁N)(CN)2] [C⁁N = bzq (3), ppy (4)], respectively. X-Ray diffraction studies of complexes 2–4 show the existence of PtII-TlI bonds. In 2·CH2Cl2 the platinum–thallium units are associated in tetranuclear Pt2Tl2 entities which generate a 3-D network through short Tl⋯π(2-py) and π⋯π(bzq) contacts and additional weak Cl2HC–H⋯π(C[triple bond, length as m-dash]C) nonclassical interactions. Compounds 3 and 4 show extended 2-D networks by connection of the organometallic “PtTl(C⁁N)(CN)2” units, through secondary Tl⋯N[triple bond, length as m-dash]C contacts and moderate π⋯π(bzq) interactions in the case of 3. Complexes 1–3 containing the bzq group exhibit in the solid state “luminescence thermochromism” associated to dual emission. At room temperature they show an intense, visible orange (1: λmax 625 nm), orange-red (2: λmax 640 nm) or yellow (3: λmax 582 nm) luminescence that changes to yellowish-green (1: λmax 532 nm) or green [2: λmax 524 nm; 3: λmax 512 nm] upon cooling to 77 K. The unstructured low energy (LE) bands attributed to 3π–π* excimeric emissions due to extensive π–π interactions are dominant at room temperature. By contrast, the high energy (HE) bands are highly structured and predominant at 77 K. Due to the presence of Pt–Tl bonds these HE emissions are bathochromically shifted in relation to the precursors′ ones and have been tentatively assigned to a metal-metal′-to-ligand (bzq) charge transfer MM′LCT [d/s σ*(Pt,Tl) →π*(C⁁N)] mixed, as in the corresponding precursors, with some intraligand 3IL[π(C⁁N′) →π*(C⁁N)] in 3 and 4 or ligand-to-ligand charge transfer (alkynyl to bzq) 3LL′CT in complexes 1 and 2. Complex [PtTl(ppy)(CN)2] 4, which does not show short contacts between the phenylpyridinate groups in solid state, only shows the HE green structured band both at 298 K and at 77 K. Only the cyanide derivatives are soluble and both spectroscopic (NMR and UV-Vis) and emission data (MeOH, 298 K and 77 K) indicate that the PtII–TlI bond breaks down in solution.

Graphical abstract: Extended structures containing Pt(ii)–Tl(i) bonds. Effect of these interactions on the luminescence of cyclometalated Pt(ii) compounds

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Publication details

The article was received on 30 Oct 2008, accepted on 18 Dec 2008 and first published on 09 Feb 2009


Article type: Paper
DOI: 10.1039/B819323A
Citation: Dalton Trans., 2009,0, 2224-2234
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    Extended structures containing Pt(II)–Tl(I) bonds. Effect of these interactions on the luminescence of cyclometalated Pt(II) compounds

    J. Forniés, S. Fuertes, A. Martín, V. Sicilia, B. Gil and E. Lalinde, Dalton Trans., 2009, 0, 2224
    DOI: 10.1039/B819323A

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