Luminescent Pt^II−M^I (M = Cu, Ag, Au) Heteronuclear Alkynyl Complexes Prepared by Reaction of [Pt(C⋮CR)₄]^2- with [M₂(dppm)₂]²⁺ (dppm = Bis(diphenylphosphino)methane)

A series of PtM, PtM2, and Pt2M3 (M = Cu, Ag, Au) heteronuclear alkynyl complexes, synthesized by reaction of the tetraalkynylplatinate(II) complexes [Pt(C⋮CR)4]2- with [M2(μ-dppm)2]2+ (dppm = bis(diphenylphosphino)methane), were characterized by elemental analyses, ESI-MS, 1H and 31P NMR spectroscopy, and X-ray crystallography for 5−13. The PtII and MI centers are linked doubly and singly by dppm in the PtM and PtM2 complexes, respectively. The Pt2Ag3 complex 13 is composed of two PtAg units associated with another Ag center by acetylide η2 (π) coordination. Strong Pt−M bonding interactions are operative, in view of their rather short distances (2.7−3.0 Å). Compounds 1−13 emit strongly in the solid state at 298 and 77 K with lifetimes in the microsecond range, indicating spin-forbidden triplet excited states. They also exhibit moderate photoluminescence in degassed dichloromethane at 298 K. The emission energy in the solid state decreases with an increase in the electron-donating ability of the R substituents, implying that the emissive origin is probably substantial ligand-to-cluster [RC⋮C→PtM] LMMCT transitions, in view of the Pt−M interactions.