Synthesis, Structure, and Characterization of Emissive Neutral Dinuclear CuI Complexes with a Tetraphosphane Bridging Ligand

Abstract

A series of new dinuclear copper complexes with a tetraphosphane bridging ligand, [{(pz 4 B)Cu} 2 (µ‐tpbz)] ( 1 ), [{(pz 2 BH 2 )Cu} 2 (µ‐tpbz)] ( 2 ), and [{(tz 2 BH 2 )Cu} 2 (µ‐tpbz)] ( 3 ) [tpbz = 1,2,4,5‐tetrakis(diphenylphosphanyl)benzene, pz 4 B = tetrakis(pyrazol‐1‐yl)borate, pz 2 BH 2 = bis(pyrazol‐1‐yl)borohydrate, and tz 2 BH 2 = bis(1,2,4‐triazol‐1‐yl)borohydrate], have been synthesized and structurally characterized. The Cu I atoms in these complexes are four‐coordinate and adopt a tetrahedral coordination geometry. In each complex, the copper centers are bridged by a tpbz ligand and each Cu I is further terminally chelated by a borate diimine anion. The central phenylene ring and the phosphine atoms of the tpbz ligand are essentially planar. The two Cu I atoms in each molecule are located above and below the (P 2 C 6 H 2 P 2 ) mean plane, respectively, leading to a chair‐like conformation for the [Cu](P 2 C 6 H 2 P 2 )[Cu] fragment. The distances between the Cu I atoms in each complex are about 8.7 Å. In the solid state, these complexes are emissive and exhibit yellow–orange photoluminescence [emission peaks, λ max = 580 nm ( 1 ), 569 nm ( 2 ), 540 nm ( 3 )] with lifetimes of 7.4–20.5 µs and quantum yields Φ = 0.07–0.45 at room temperature. Theoretical and experimental results indicate that these complexes have the lowest singlet (S 1 ) state and the lowest triplet (T 1 ) state with very close energy levels, and display thermally activated delayed fluorescence (TADF) at ambient temperature.