Impact of Intermolecular Non-Covalent Interactions in a Cu^I ₈ Pd^II ₁ Discrete Assembly: Conformers' Geometries and...

A new highly solid-state luminescent phase of a previously reported weakly luminescent Cu^I ₈ Pd^II ₁ dicationic assembly is reported revealing the high geometrical versatility of this moiety that importantly alters its luminescent properties. This very minor new species B_c is based on a different conformer scaffold than the one encountered in the previously reported B_o form and, essentially differs from B_o by displaying shorter Cu^I -Cu^I intermetallic distances. DFT calculations allow concluding that the predominance in the solid-state of the weakly luminescent and less stable B_o phase is due to the extra stability induced by a larger number of intermolecular non-covalent π-CH interactions in its crystalline packing and not by the intrinsic stability of the Cu^I ₈ Pd^II ₁ dicationic moiety. Calculations also revealed that a more stable conformation B_calc is expected in vacuum, which bears a different distribution of Cu^I -Cu^I intermetallic distances than the dications in B_o and B_c phases. Taking into account that the geometrical alterations are associated to drastic changes of luminescence properties, this confer to the Cu^I ₈ Pd^II ₁ assembly high potentiality as stimuli-sensitive luminescent materials. Indeed, by applying mechanical or thermal stress to samples of B_o phase, new phases B_g and B_m , respectively, were obtained. Alterations of the solid-state photophysical properties of these new species compared to those recorded for B_o are reported together with a combined experimental and computed study of the structures/properties relationships observed in these phases.