Synthesis, Structures, and Luminescence Behavior of Mixed Metal Alkynyl Platinum−Cadmium Complexes§

This article describes the preparation, characterization, and optical properties of new bi- and trinuclear tweezer-type platinum cadmium derivatives, stabilized by η 2 -alkyne-cadmium bonding. Treatment of Q 2 [cis-Pt(C 6 F 5 ) 2 (C=CR) 2 ] (la-lc) with CdCl 2 ·2,5 H 2 O (1:1) produces dinuclear Pt-Cd adducts Q 2 -[{cis-Pt(C 6 F 5 ) 2 (m-κC α :η 2 -C=CR) 2 }(CdCl 2 )] (Q = NBu 4 , R = t-Bu 2a; Q = PMePh 3 , R = Ph 2b; R = Tol 2c). However, reaction of (NBu 4 ) 2 [cis-Pt(C6F5)2(C=CR)2] with Cd(NO 3 ) 2 ·4H 2 O produces trinuclear Pt 2 Cd dianionic complexes (NBu 4 ) 2 [{cis-Pt(C 6 F 5 ) 2 (μ-κC α :η 2 -C≡CR) 2 } 2 Cd] (3a-3c). The analogous (PMePh 3 ) 2 [{cis-Pt(C 6 F 5 ) 2 (μ-κC α :η 2 -C≡CR) 2 } 2 Cd] (R = Ph 3b'; Tol 3c') were prepared similarly starting from (PMePh 3 ) 2 [cis-Pt(C6F5)2(C=CR) 2 ]. The crystal structures of 2c and 3a,b show that the cadmium center is well embedded by the cis-bis(alkyne)platinate entities, leading to planar PtC 4 Cd cores. In the heterometallic species, the low-energy absorption, which is ascribed to an admixture of π → π*(C≡CR) IL/dπ(Pt) → π*(C≡CR) MLCT, exhibits a clear hypsochromic shift compared to its precursors, probably due to the existence of a lesser delocalization on the alkynyl fragments upon the η 2 -complexation. The arylalkynyl derivatives (b, c) display intense structured emission bands, arising from 3 ππ*(C≡CR) (IL) and/or mixed 3 ππ*/Pt(d π )(C≡CR) → π*(C≡CR) ( 3 MLCT) manifolds with a predominant IL character.