Subtle Influences of a Flexible Tecton on an R₂²(8) Carboxyl Dimer Synthon: From Molecular Threading to 2D → 3D Interpenetration

Abstract

The use of well-defined synthons and rigid tectons has allowed for great advancement in the reticular synthesis of hydrogen-bonded organic frameworks. However, the use and influence of flexible tectons on the well-reported R2 2(8) carboxyl dimer synthon is a largely unexplored area. As part of our investigation, we report here the structures of ten polymorphs/pseudopolymorphs (1–10) of the flexible tecton 3-[2,5,5′-tris­(2′-carboxyethyl)-1,1′-dioxo-1″λ6-thiolan-2″-yl]­propanoic acid (L). L provided a rich variety of structures, which were described using three identified key structural motifs: a zigzag 1D chain, a dimer which may extend into a 1D chain, and a (4,4) net. Structure 3 consisted of a 1D chain, and structures 2, 5, 8, and 9 were 3D assemblies described using the dimer motif. Structures 4, 6, and 7 formed 1D chains of dimers as well as (4,4) nets, and these two motifs were stacked alternately in the overall structures. The structure of 1 formed a 1D zigzag chain which was threaded through a (4,4) net. The structure of 10 did not contain any of these motifs and instead consisted of a (6,6) net which was 4-fold interpenetrated. Solvent guest molecules were found to have no effect on the resulting structures. The carboxyl dimer synthon was present in 9 of the 10 reported structures. However, the flexibility of the tecton, while it gave rise to a diverse range of structures, resulted in limited control over the final assemblies.

Combined NMR Spectroscopy and Quantum-Chemical Calculations in Fluorescent 1,2,3-Triazole-4-carboxylic Acids Fine Structures Analysis

“…in solution using different non-covalent interactions [30][31][32][33]. Since the presence of a carboxyl group causes molecules to form various aggregates, in a continuation of our work on the design of a new effective fluorophore based on a 1,2,3-triazole core, we should evaluate the extent of their ability to form NCIs [34][35][36][37][38].…”

Vibrational mode analysis of hydrogen-bonded organic frameworks (HOFs): synchrotron infrared studies

“…This is indeed a substantial interaction between subunits acting to stabilize the framework, consistent with hydrogen-bonding in other crystalline solids displaying the R 2 2 (8) synthon. 42 The broad hydrogen-bonding band for the synthesized sample is in contrast to the resolved, narrow peaks of the fingerprint region (below 1600 cm À1 ), which are associated with the ring deformation vibrational modes intrinsic to the TP 2À and Cta 4+ components. In the synchrotron mid-IR spectra, most prominent bands are observed to align with predicted vibrational frequencies of either the HOF unit cell (1), or the Fig.…”

“…This is indeed a substantial interaction between subunits acting to stabilize the framework, consistent with hydrogen-bonding in other crystalline solids displaying the R 2 2 (8) synthon. 42…”

“…51 This code has been previously used by our workgroup to calculate vibrational frequencies for molecular crystals 31 and flexible networks involving hydrogen-bonded carboxyl dimer synthons. 42 Resultant synthetic far-IR spectra have been demonstrated of sufficient accuracy 52,53 to assign features originating from large-amplitude, low-frequency intermolecular lattice modes and intramolecular torsion vibrations that are prevalent in HOF systems but can otherwise be difficult to model using non-periodic descriptions. Herein, the B3LYP hybrid functional and modified 6-311G(d), triple-z quality basis sets 54 are employed for the electronic structure calculations.…”

“…38,39 In the specific case of MOFs and HOFs, such lattice modes are often coupled to low-lying intramolecular modes arising from the deformation and torsional motion of organic linker and aromatic spacer units. 36 As well as information on the neat framework as synthesized or after activation, IR studies have also provided insight toward host-guest interactions, [40][41][42] where the presence of solvent or guest molecule -typically bound to specific sites on the pore surface -acts to perturb the equilibrium vibrational and lattice frequencies of the host framework.…”