Impact of Intermolecular Non-Covalent Interactions in a (Cu8Pd1II)-Pd-I Discrete Assembly: Conformers' Geometries and Stimuli-Sensitive Luminescence Properties

A new highly solid-state luminescent phase of a previously reported weakly luminescent (Cu8Pd1II)-Pd-I 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 pi-CH interactions in its crystalline packing and not by the intrinsic stability of the (Cu8Pd1II)-Pd-I 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 (Cu8Pd1II)-Pd-I 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.