Interpreting the different emissive properties of cyclic tri­imidazole-based Cu(I) and Ag(I) coordination polymers: a QTAIM and IQA study

A QTAIM and IQA investigation on model compounds of two isostructural Ag(I) and Cu(I) coordination polymers (CPs) based on cyclic tri­imidazole (L), i.e. the [MIL]( n ) 1D double-stranded stair chain and the [MClL]( n ) 3D network (M = Cu, Ag), has allowed light to be shed on the different emissive behaviour associated with the two metal ions. According to a previously reported investigation [Malpicci et al. (2021). Inorg. Chem. Front. 8, 1312–1323 ▸], Ag(I) CPs showed both fluorescence and multiple ligand-centred room-temperature phospho­rescences, whereas Cu(I) CPs displayed non-thermally equilibrated halogen and metal-to-ligand charge transfer and two ligand-centred phospho­rescences, the latter observed only by their selective activation. Analysis of both local and integral QTAIM descriptors, including delocalization indices and source function, of the Ag—N and Cu—N bonds reveals a higher covalent and local character for the latter, explaining the greater metal–ligand electronic communication observed for the Cu compounds. Moreover, IQA investigation shows that the Cu—N bond is characterized by higher interaction energy, due to both higher electrostatic and exchange-correlation contributions. Analysis on the M—X (M = Ag, Cu; X = I, Cl) bonds, also present in these structures, highlights a much higher covalent and local character with respect to the M—N bonds.