Phosphorescent Decanuclear Bimetallic Pt₆M₄ (M = Zn, Fe) Tetrahedral Cages

Coordination-driven self-assembly delivers discrete, nanoscopic architectures that may preserve or enhance the physicochemical properties of their parent building blocks. Herein, we report the syntheses, characterization, and photophysical properties of two tetrahedral cages, [Zn^II₄L₆](PF₆)₈ (C1) and [Fe^II₄L₆](OTf)₈ (C2), where L = Pt^II(PEt₃)₂(C≡C-bpy)₂ (PEt₃ = triethylphosphine; C≡C-bpy = 5-ethynyl-2,2'-bipyridine) and OTf = trifluoromethanesulfonate. C1 and C2 were assembled in isolated yields of 72% and 81% by treating 2 equiv of Zn(NO₃)₂·6H₂O or Fe(OTf)₂ with 3 equiv of L, respectively. Both cages were fully characterized by NMR, electrospray ionization mass spectrometry, and single-crystal X-ray diffraction (SCXRD). The local D₃ symmetry at each polypyridyl metal node raises the possibility of a number of isomeric cages; however, only the homochiral enantiomers (ΔΔΔΔ and ΛΛΛΛ) are formed based on ¹H NMR and SCXRD. C1 exhibits phosphorescence centered at 545 nm with a quantum yield of 10% in N₂-degassed acetonitrile at 25 °C. The quantum yield of C2 is significantly lower due to a nonradiative relaxation from ⁵MC (MC = metal-centered) states introduced by the Fe^II nodes.