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

Abstract

The series of cyanide-bridged coordination polymers [(P² )CuCN]_n (1), [(P² )Cu{M(CN)₂ }]_n (M=Cu 3, Ag 4, Au 5) and molecular tetrametallic clusters [{(P⁴ )MM'(CN)}₂ ]²⁺ (MM'=Cu₂ 6, Ag₂ 7, AgCu 8, AuCu 9, AuAg 10) were obtained using the bidentate P² and tetradentate P⁴ phosphane ligands (P² =1,2-bis(diphenylphosphino)benzene; P⁴ =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 d¹⁰ -d¹⁰ 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 T₁ and S₁ 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 484-650 nm 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 ΔE(S₁ -T₁ ). 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.