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

Abstract

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) 2 (4,4′-bipy)]·DMF} n ( P1A, P1B ; Pip = piperonylic acid; 4,4′-bipy = 4,4′-bipyridine). Besides, [Hg(Pip) 2 (4,4′-bipy)] n ( 2 ) has been achieved during the attempts to isolate these polymorphs. The selective synthesis of P1A and P1B 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 P1A and P1B 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 P1B , which shows Hg(II) geometries that are further from ideality, is more stable than P1A by 13 kJ·mol –1 per [Hg(Pip) 2 (4,4′-bipy)]·DMF formula unit, and this larger stability of P1B 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.

Water Content-Controlled Formation and Transformation of Concomitant Pseudopolymorph Coordination Polymers

“…Although this event is rather rare, there are some reports about it. In a few interesting cases, supramolecular isomers were formed in the reaction vessel concomitantly. − Although structural transformation of CPs in the solid phase is highly regarded, − there are few studies on the structural transformation in the liquid phase in CPs, especially through dissolution–recrystallization structural transformation (DRST). ,,,− …”

Amide-Driven Secondary Building Unit Structural Transformations between Zn(II) Coordination Polymers

“…Under irradiation, the CPs show unstructured emission signals suggesting charge transfer transitions (Figure ). All the emission spectra present one common emission maxima (λ max‑em ) centered at 361 nm with a Stokes shift of 3549 cm –1 . This band could be assigned to the 4,4′-bipy ligand because it emits in this region when excited at 323 nm .…”

From Cu(i) and Cu(i)–Cu(ii) mixed-valence clusters to 2D Cu(ii) and Cu(i) coordination polymers supported by a flexible bis-tetrazole organosulfur ligand

“…4 Therefore, despite polymorphism being a well-known phenomenon, very few cases have been described in the field of coordination polymers. 5…”