New Dicyano Cyclometalated Compounds Containing Pd(II)–Tl(I) Bonds as Building Blocks in 2D Extended Structures: Synthesis, Structure, and Luminescence Studies

New mixed metal complexes [PdTl­(C∧N)­(CN)2] [C∧N = 7,8-benzoquinolinate (bzq, 3); 2-phenylpyridinate (ppy, 4)] have been synthesized by reaction of their corresponding precursors (NBu4)­[Pd­(C∧N)­(CN)2] [C∧N = bzq (1), ppy (2)] with TlPF6. Compounds 3 and 4 were studied by X-ray diffraction, showing the not-so-common PdII–TlI bonds. Both crystal structures exhibit 2-D extended networks fashioned by organometallic “PdTl­(C∧N)­(CN)2” units, each one containing a donor–acceptor Pd­(II)–Tl­(I) bond, which are connected through additional Tl···NC contacts and weak Tl···π (bzq) contacts in the case of 3. Solid state emissions are red-shifted compared with those of the precursors and have been assigned to metal–metal′-to-ligand charge transfer (MM′LCT [d/s σ*­(Pd,Tl) → π*­(C∧N)]) mixed with some intraligand (3IL­[π­(C∧N) → π*­(C∧N)]) character. In diluted solution either at room temperature or 77 K, the Pd–Tl bond is no longer retained as confirmed by mass spectrometry, NMR, and UV–vis spectroscopic techniques.