Highly Luminescent Half-Lantern Cyclometalated Platinum(II) Complex: Synthesis, Structure, Luminescence Studies, and Reactivity.

The half-lantern compound [{Pt­(bzq)­(μ-C₇H₄NS₂-κN,S)}₂]·Me₂CO (<b>1</b>) was obtained by reaction of equimolar amounts of potassium 2-mercaptobenzothiazolate (KC₇H₄NS₂) and [Pt­(bzq)­(NCMe)₂]­ClO₄. The Pt­(II)···Pt­(II) separation in the neutral complex [{Pt­(bzq)­(μ-C₇H₄NS₂-κN,S)}₂] is 2.910 (2) Å, this being among the shortest observed in half-lantern divalent platinum complexes. Within the complex, the benzo­[<i>h</i>]­quinoline (bzq) groups lie in close proximity with most C···C distances being between 3.3 and 3.7 Å, which is indicative of significant π–π interactions. The reaction of <b>1</b> with halogens X₂ (X₂ = Cl₂, Br₂, or I₂) proceeds with a two-electron oxidation to give the corresponding dihalodiplatinum­(III) complexes [{Pt­(bzq)­(μ-C₇H₄NS₂-κN,S)­X}₂] (X = Cl <b>2</b>, Br <b>3</b>, I <b>4</b>). Their X-ray structures confirm the retention of the half-lantern structure and the coordination mode of the bzq and the bridging ligand μ-C₇H₄NS₂-κN,S. The Pt–Pt distances (Pt–Pt = 2.6420(3) Å <b>2</b>, 2.6435(4) Å <b>3</b>, 2.6690(3) Å <b>4</b>) are shorter than that in <b>1</b> because of the Pt–Pt bond formation. Time dependent-density functional theory (TD-DFT) studies performed on <b>1</b> show a formal bond order of 0 between the metal atoms, with the 6p_<i>z</i> contribution diminishing the antibonding character of the highest occupied molecular orbital (HOMO) and being responsible for an attractive intermetallic interaction. A shortening of the Pt–Pt distance from 2.959 Å in the ground state S₀ to 2.760 Å in the optimized first excited state (T₁) is consistent with an increase in the Pt–Pt bond order to 0.5. In agreement with TD-DFT calculations, the intense, structureless, red emission of <b>1</b> in the solid state and in solution can be mainly attributed to triplet metal–metal-to-ligand charge transfer (³MMLCT) [dσ*­(Pt–Pt) → π*­(bzq)] excited states. The high quantum yields of this emission measured in toluene (44%) and solid state (62%) at room temperature indicate that <b>1</b> is a very efficient and stable ³MMLCT emitter, even in solution. The high luminescence quantum yield of its red emission, added to its neutral character and the thermal stability of <b>1</b>, make it a potential compound to be incorporated as phosphorescent dopant in multilayer organic light-emitting devices (OLEDs)