Intra-Cation versus Inter-Cation π-Contacts in [Cu(P^P)(N^N)][PF6] Complexes

Abstract

A series of [Cu(POP)(N^N][PF6] and [Cu(xantphos)(N^N][PF6] compounds has been prepared and characterized in which POP = bis[2-(diphenylphosphanyl)phenyl]ether (IUPAC PIN oxydi(2,1-phenylene)bis(diphenylphosphane), xantphos = 4,5-bis(diphenylphosphanyl)-9,9-dimethyl-9H-xanthene (IUPAC PIN (9,9-dimethyl-9H-xanthene- 4,5-diyl)bis(diphenylphosphane)) and the N^N ligands are 4-(4-bromophenyl)-6,6′-dimethyl-2,2′- bipyridine (1), 5,5′-bis(3-methoxyphenyl)-6-methyl-2,2′-bipyridine (2), and 6-benzyl-2,2′-bipyridine (3). The single crystal structures of [Cu(xantphos)(1)][PF6]·CH2Cl2, [Cu(xantphos)(2)][PF6]·CH2Cl2 and [Cu(POP)(3)][PF6]·0.5H2O were determined by X-ray diffraction. Each complex contains a copper(I) ion in a distorted tetrahedral environment with chelating N^N and P^P ligands. In the [Cu(xantphos)(1)]+ and [Cu(xantphos)(2)]+ cations, there are face-to-face π-stackings of bpy and PPh2 phenyl rings (i.e., between the ligands); in addition in [Cu(xantphos)(2)][PF6]·CH2Cl2, inter-cation π-embraces lead to the formation of infinite chains as a primary packing motif. In [Cu(POP)(3)][PF6]·0.5H2O, centrosymmetric pairs of [Cu(POP)(3)]+ cations engage in C–H…π (phenyl to bpy) and offset face-to-face (bpy…bpy) contacts. The electrochemical and photophysical properties of the compounds containing ligands 1 and 2 are reported. They are green or yellow emitters in the solid-state (λem in the range 535–577 nm) with values for the photoluminescence quantum yield (PLQY) in the range 19%–41%.