Cyanide-Assembled d10 Coordination Polymers and Cycles: Excited State Metallophilic Modulation of Solid-State Luminescence

The series of cyanide-bridged coordination polymers [(P-2)CuCN](n) (1), [(P-2)Cu{M(CN)(2)}](n) (M = Cu 3, Ag 4, Au 5) and molecular tetrametallic clusters [{(P-4)MM'(CN)}(2)](2+) (MM' = Cu-2 6, Ag-2 7, AgCu 8, AuCu 9, AuAg 10) were obtained using the bidentate P-2 and tetradentate P-4 phosphane ligands (P-2 = 1,2-bis(diphenylphosphino)benzene; P-4 = tris(2-diphenylphosphinophenyl)phosphane). All title complexes were crystallographically characterized to reveal a zig-zag chain arrangement for 1 and 3-5, whereas 6-10 possess metallocyclic frameworks with different degree of metal-metal bonding. The d(10)-d(10) interactions were evaluated by the quantum theory of atoms in molecules (QTAIM) computational approach. The photophysical properties of 1-10 were investigated in the solid state and supported by theoretical analysis. The emission of compounds 1 and 3-5, dominated by metal-to-ligand charge transfer (MLCT) transitions located within {CuP2} motifs, is compatible with thermally activated delayed fluorescence (TADF) behaviour and a small energy gap between the T-1 and S-1 excited states. The luminescence characteristics of 6-10 are strongly dependent on the composition of the metal core; the emission band maxima vary in the range 484-650nm with quantum efficiency reaching 0.56 (6). The origin of the emission for 6-8 and 10 at room temperature is assigned to delayed fluorescence. AuCu cluster 9, however, exhibits only phosphorescence that corresponds to theoretically predicted large value Delta E(S-1-T-1). DFT simulation highlights a crucial impact of metallophilic bonding on the nature and energy of the observed emission, the effect being greatly enhanced in the excited state.