An Extended chain and trinuclear complexes based on pt(II)-M (M = Tl(I), Pb(II)) bonds: Contrasting photophysical behavior

Abstract

The syntheses and structural characterizations of a Pt-Tl chain [{Pt(bzq)(C<inf>6</inf>F<inf>5</inf>)<inf>2</inf>}Tl(Me<inf>2</inf>CO)]<inf>n</inf> 1 and two trinuclear Pt<inf>2</inf>M clusters (NBu<inf>4</inf>)[{Pt(bzq)(C<inf>6</inf>F<inf>5</inf>)<inf>2</inf>}<inf>2</inf>Tl] 2 and [{Pt(bzq)(C<inf>6</inf>F<inf>5</inf>)<inf>2</inf>}<inf>2</inf>Pb] 3 (bzq = 7,8-benzoquinolinyl), stabilized by donor-acceptor Pt → M bonds, are reported. The one-dimensional heterometallic chain 1 is formed by alternate "Pt(bzq)(C<inf>6</inf>F<inf>5</inf>)<inf>2</inf>" and "Tl(Me<inf>2</inf>CO)" fragments, with Pt-Tl bond separations in the range of 2.961(1)-3.067(1) Å. The isoelectronic trinuclear complexes 2 (which crystallizes in three forms, namely, 2a, 2b, and 2c) and 3 present a sandwich structure in which the Tl(I) or Pb(II) is located between two "Pt(bzq)(C<inf>6</inf>F<inf>5</inf>)<inf>2</inf>" subunits. NMR studies suggest equilibria in solution implying cleavage and reformation of Pt-M bonds. The lowest-lying absorption band in the UV-vis spectra in CH<inf>2</inf>Cl<inf>2</inf> and tetrahydrofuran (THF) of 1, associated with 1MLCT/1L′LCT 1[5d<inf>π</inf>(Pt) → π∗(bzq)]/1[(C<inf>6</inf>F<inf>5</inf>) → bzq], displays a blue shift in relation to the precursor, suggesting the cleavage of the chain maintaining bimetallic Pt-Tl fragments in solution, also supported by NMR spectroscopy. In 2 and 3, it shows a blue shift in THF and a red shift in CH<inf>2</inf>Cl<inf>2</inf>, supporting a more extensive cleavage of the Pt-M bonds in THF solutions than in CH<inf>2</inf>Cl<inf>2</inf>, where the trinuclear entities are predominant. The Pt-Tl chain 1 displays in solid state a bright orange-red emission ascribed to 3MM′CT (M′ = Tl). It exhibits remarkable and fast reversible vapochromic and vapoluminescent response to donor vapors (THF and Et<inf>2</inf>O), related to the coordination/decoordination of the guest molecule to the Tl(I) ion, and mechanochromic behavior, associated with the shortening of the intermetallic Pt-Tl separations in the chain induced by grinding. In frozen solutions (THF, acetone, and CH<inf>2</inf>Cl<inf>2</inf>) 1 shows interesting luminescence thermochromism with emissions strongly dependent on the solvent, concentration, and excitation wavelengths. The Pt<inf>2</inf>Tl complex 2 shows an emission close to 1, ascribed to charge transfer from the platinum fragment to the thallium [3(L+L′)MM′CT]. 2 also shows vapoluminescent behavior in the presence of vapors of Me<inf>2</inf>CO, THF, and Et<inf>2</inf>O, although smaller and slower than those of 1. The trinuclear neutral complex Pt<inf>2</inf>Pb 3 displays a blue-shift emission band, tentatively assigned to admixture of 3MM′CT 3[Pt(d) → Pb(sp)] with some metal-mediated intraligand (3ππ/3ILCT) contribution. In contrast to 1 and 2, 3 does not show vapoluminescent behavior. © 2015 American Chemical Society.