Controlling the Formation of Two Concomitant Polymorphs in Hg(II) Coordination Polymers.

Controlling the formation of the desired product in the appropriate crystalline form is the fundamental breakthrough of crystal engineering. On that basis, the preferential formation between polymorphic forms, which are referred to as different assemblies achieved by changing the disposition or arrangement of the forming units within the crystalline structure, is one of the most challenging topics still to be understood. Herein, we have observed the formation of two concomitant polymorphs with general formula {[Hg(Pip)(4,4'-bipy)]·DMF} (; Pip = piperonylic acid; 4,4'-bipy = 4,4'-bipyridine). Besides, [Hg(Pip)(4,4'-bipy)] () has been achieved during the attempts to isolate these polymorphs. The selective synthesis of and has been successfully achieved by changing the synthetic conditions. The formation of each polymorphic form has been ensured by unit cell measurements and decomposition temperature. The elucidation of their crystal structure revealed and as polymorphs, which originates from the Hg(II) cores and intermolecular associations, especially pinpointed by Hg···π and π···π interactions. Density functional theory (DFT) calculations suggest that , which shows Hg(II) geometries that are further from ideality, is more stable than by 13 kJ·mol per [Hg(Pip)(4,4'-bipy)]·DMF formula unit, and this larger stability of arises mainly from metal···π and π···π interactions between chains. As a result, these structural modifications lead to significant variations of their solid-state photoluminescence.