Luminescent Benzoquinolate-Isocyanide Platinum(II) Complexes: Effect of Pt⋅⋅⋅Pt and π⋅⋅⋅π Interactions on their Photophysical Properties
The neutral compounds [Pt(bzq)(CN)(CNR)] (R = tBu (1), Xyl (2), 2-Np (3); bzq = benzoquinolate, Xyl = 2,6-dimethylphenyl, 2-Np = 2-napthyl) were isolated as the pure isomers with a trans-C(bzq),CNR configuration, as confirmed by (13)C{(1)H} NMR spectroscopy in the isotopically marked [Pt(bzq)((13)CN)(CNR)] (R = tBu (1'), Xyl (2'), 2-Np (3')) derivatives (δ(13)C(CN) ≈ 110 ppm; (1) J(Pt,(13)C) ≈ 1425 Hz]. By contrast, complex [Pt(bzq)(C≡CPh)(CNXyl)] (4) with a trans-N(bzq),CNR configuration, has been selectively isolated from [Pt(bzq)Cl(CNXyl)] (trans-N(bzq),CNR) using Sonogashira conditions. X-ray diffraction studies reveal that while 1 adopts a columnar-stacked chain structure with Pt-Pt distances of 3.371(1) Å and significant π⋅⋅⋅π interactions (3.262 Å), complex 2 forms dimers supported only by short Pt⋅⋅⋅Pt (3.370(1) Å) interactions. In complex 4 the packing is directed by weak bzq⋅⋅⋅Xyl and bzq⋅⋅⋅C≡E (C, N) interactions. In solid state at room temperature, compounds 1 and 2 both show a bright red emission (ϕ = 42.1% 1, 57.6% 2). Luminescence properties in the solid state at 77 K and concentration-dependent emission studies in CH(2)Cl(2) at 298 K and at 77 K are also reported for 1-4.