The Influence of Cyclometalated Ligand Motifs on the Solid-State Assemblies and Luminescent Properties of Pt(II)-Tl(I) Complexes

We have synthesized the HC^Npz ligand, 1-(naphthalen-2-yl)-1H-pyrazole (1A), and carried out its cyclometalation reaction with [{Pt­(η3-C4H7)­(μ-Cl)}2] to give [{Pt­(Naph^N)­(μ-Cl)}2]. This process takes place via the intermediate [Pt­(η3-C4H7)­Cl­(HNaph^N-κN)] (2A) which could be isolated and fully characterized. Compound [{Pt­(Naph^N)­(μ-Cl)}2] and the analogous N-heterocyclic carbene complex [{Pt­(Naph^C*)­(μ-Cl)}2] (HNaph^C*-κC* = 3-methyl-1-(naphthalen-2-yl)-1H-imidazol-2-ylidene) were used to prepare the bis-cyanide anionic derivatives NnBu4­[Pt­(Naph^E)­(CN)2] (E = Npz4A, C*carbene4B) which subsequently react with TlPF6 to afford the corresponding complexes [PtTl­(Naph^E)­(CN)2] (5A and 5B). The X-ray structures of 5A and 5B show the presence of 2D extended networks created by organometallic “PtTl­(Naph^E)­(CN)2” entities, each one containing a Pt→Tl dative bond (d Pt–Tl = 3.0205(3) Å 5A, 2.9395(4) Å 5B). These units are linked together through additional Tl···N≡C and Tl···π contacts, which, in the case of 5B, renders a stair-like arrangement. NBO charge distributions analysis on 4A and 4B shows a small negative charge on the Pt center for 4B, while positive for 4A, indicating the more electron donating character of the carbene with respect to the pyrazole group. 195Pt and 13C NMR spectra of NnBu4­[Pt­(Naph^E)­(13CN)2] (E = Npz4A′, C*carbene4B′) account for this difference. Photophysical analysis has been performed for 4A/B and 5A/B regarding the Naph^E fragment. The emissions of 4A and 4B in CH2Cl2 at 77 K present similar profiles and have been assigned to 3ILCT [π­(Naph^E) → π*­(Naph^E)] excited states. The green emission of 4A in poly­(methyl methacrylate) (PMMA) film (5 wt %) affords a photoluminescence quantum yield (PLQY, Φ) of 82%. In the solid state, the vibronic emissions of 5A (λmax = 528 nm) and 5B (λmax = 561 nm) are red-shifted in relation to their precursors (λmax = 488nm 4A, 530nm 4B) and are mainly attributed to 3MM′LCT [d/s σ*­(Pt,Tl) → π*­(Naph^E)] excited states.