Sánchez-Férez F, Solans-Monfort X, Calvet T, Font-Bardia M, Pons J. Controlling the Formation of Two Concomitant Polymorphs in Hg(II) Coordination Polymers.
Inorg Chem 2022;
61:4965-4979. [PMID:
35298147 PMCID:
PMC8965880 DOI:
10.1021/acs.inorgchem.1c03762]
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Abstract
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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.
We have successfully isolated two concomitant
polymorphs
with formula {[Hg(Pip)2(4,4′-bipy)]·DMF}n (P1A and P1B), as
well as their desolvated form 2. Then, both polymorphs
were selectively synthesized by temperature or anion-template formation.
Their crystal structures revealed distorted pentagonal pyramidal geometries
and show that differences arise from geometry and packing that led
to different solid-state photoluminescence emissions. According to
periodic-DFT calculations, distortions in P1B are counterbalanced
leading to a more stable form by Hg(II)···π and
π···π interactions.
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