Cyclometalated Platinum(II) Cyanometallates: Luminescent Blocks for Coordination Self-Assembly

A family of cyanide-bridged heterometallic aggregates has been constructed of the chromophoric cycloplatinated metalloligands and coordinatively unsaturated d¹⁰ fragments {M­(PPh₃)_n}. The tetranuclear complexes of general composition [Pt­(C^N)­(CN)₂M­(PPh₃)₂]₂ [C^N = ppy, M = Cu (1), Ag (2); C^N = tolpy (Htolpy = 2-(4-tolyl)-pyridine), M = Cu (4), Ag (5); C^N = F₂ppy (HF₂ppy = 2-(4, 6-difluorophenyl)-pyridine), M = Cu (7), Ag (8)] demonstrate a squarelike arrangement of the molecular frameworks, which is achieved due to favorable coordination geometries of the bridging ligands and the metal ions. Variation of the amount of the ancillary phosphine (for M = Ag) afforded compounds [Pt­(C^N)­(CN)₂Ag­(PPh₃)]₂ (C^N = ppy, 3; C^N = tolpy, 6); for the latter one an alternative cluster topology, stabilized by the Pt–Ag metallophilic and η¹-C_ipso(C^N)–Ag bonding, was observed. The solid-state structures of all of the title species 1–8 were determined crystallographically. The complexes exhibit moderately strong room-temperature phosphorescence as crystalline powders (Φ_em = 16–34%, λ_em = 470–511 nm). The luminescence studies and time-dependent density functional theory computational analysis indicate that the photophysical behavior is dominated by the ³π–π* electronic transitions localized on the cyclometalated fragment and mixed with M_PtLCT contribution, while the d¹⁰-phosphine motifs have a negligible contribution into the frontier orbitals and therefore show a little influence on the emission performance of the described compounds.