Preparation of Pt–Tl clusters showing new geometries. X-ray, NMR and luminescence studies

Abstract

Square planar complexes [Pt(CNC)L] (CNC = C,N,C-2,6-NC₅H₃(C₆H₄-2)₂; L = tht (tetrahydrothiophene, SC₄H₈, 1), L = CN^tBu (2)) react with TlPF₆ in different Pt/Tl molar ratios (3/1 in the case of 1 and 1/1 in the case of 2) yielding the complexes [{Pt(CNC)(tht)}₃Tl](PF₆) (3) and [Pt(CNC)(CN^tBu)Tl](PF₆) (4), respectively. The structures of 3 and 4 (X-ray) show the presence of Pt→Tl dative bonds unsupported by any bridging ligands. In complex 3, the only Tl centre is simultaneously bonded to three Pt atoms forming a perfect equilateral triangle with Pt–Tl distances of 2.9088(5) Å, remarkably short. Complex 4 is formed by three “Pt(CNC)(CN^tBu)Tl” units, disposed in a triangular fashion, linked together through η⁶-Tl–arene interactions, and showing Pt–Tl bonds with distances of ca. 3.04 Å. The study of these crystal structures would seem to indicate that the difference between the Pt/Tl ratios found in the complexes 3 and 4 is due to the steric requirements of the L ligand bonded to Pt. NMR studies both in solution and in the solid state show that the Pt–Tl bond persists in solutions of 3 and 4. The UV-vis spectra of 3 and 4 in solution display the same profiles as those of 1 and 2, which may suggest a partial dissociation of the Pt–Tl bond in solution. However, by DFT calculations it was proved that in this case the formation of the Pt–Tl dative bond does not produce the expected blue-shift in the UV-vis absorptions. The emissive behaviour of 1–4 in the solid state and in frozen solutions is also studied and included in this work.