The ability to achieve structural diversity in metal-organic frameworks (MOFs) from a single set of metal and organic ligand precursors represents a significant advancement in materials design. This study demonstrates that solvent composition can act as a powerful external control parameter to modulate the coordination behavior of flexible ligands toward Cu(II), leading to distinct secondary building units (SBUs) and resulting MOF topologies. Specifically, trans,trans-muconic acid (H₂muco), a flexible dicarboxylic ligand with hydrophilic terminal groups, exhibits two different coordination modes depending on the solvent environment: water-rich or DMF-rich conditions. In water-rich systems, H₂muco coordinates to Cu(II) in a monodentate fashion, forming a one-dimensional (1D) chain structure stabilized by bridging water molecules. Conversely, in DMF-rich environments, the ligand adopts a bidentate coordination mode, facilitating the formation of paddle-wheel SBUs and a two-dimensional (2D) square net architecture. The transition between these structures is driven by solvent-mediated interactions, particularly hydrogen bonding between water molecules and the keto oxygen of the muco²⁻ ligand, which suppresses bidentate coordination in aqueous media. In contrast, the reduced hydrogen-bonding capacity in DMF-rich solvents allows for more extensive carboxylate coordination, enabling the formation of the characteristic paddle-wheel motif.Brk Antibody supplier This work highlights the critical role of solvent in directing molecular assembly and provides a new strategy for achieving structural tunability in late transition metal MOFs through rational solvent selection.
Mechanistic Insights into Solvent-Controlled Coordination Modes
The observed structural divergence arises from a delicate balance between ligand-solvent interactions and metal-ligand affinity. In water-rich conditions, the presence of bulk water promotes strong hydrogen bonding with the carbonyl oxygens of the muco²⁻ anion, effectively blocking the keto oxygen from coordinating to Cu(II). This forces the ligand to bind via a single carboxylate group in a monodentate manner, resulting in linear 1D chains where each Cu(II) ion is six-coordinated with two carboxylate oxygens, two water molecules, and two additional ligands from adjacent chains. These chains are further linked by bridging water molecules, creating extended networks. In contrast, in DMF-rich mixtures, the formation of a reverse micelle-like microenvironment—where water forms the core surrounded by DMF—minimizes hydrogen bonding with the ligand. This releases the keto oxygen, allowing it to participate in bidentate chelation with Cu(II), thereby stabilizing the paddle-wheel SBU. Each Cu(II) ion in this configuration is coordinated by four carboxylate groups from two muco²⁻ ligands and two axial DMF molecules, forming a planar octahedral geometry. The resulting 2D layers stack along the a-axis and interpenetrate, eliminating internal void space. Kinetic studies using deuterated water (D₂O) confirmed the essential role of hydrogen bonding in the initial nucleation step, as crystallization was significantly slower in D₂O due to weaker hydrogen bonds compared to H₂O, supporting the proposed mechanism.TFIIB Antibody medchemexpress
Versatility Across Ligand Families and Implications for MOF Design
The principle of solvent-guided coordination variation extends beyond muconic acid. A similar effect was observed using fumaric acid (H₂fum), a shorter analog with comparable functionality. In water-rich conditions, fumarate formed a 1D chain structure (Cufumwater), while in DMF-rich environments, it assembled into a 2D paddle-wheel network (CufumDMF).PMID:34714748 Despite structural similarities, key differences emerged: CufumDMF exhibited alternating DMF and water molecules occupying axial sites, whereas CumucoDMF had only DMF. This discrepancy stems from the shorter length of fumarate, which restricts rotational freedom of coordinated DMF molecules. Furthermore, CufumDMF displayed a 47% pore volume, unlike the non-porous CumucoDMF, indicating greater structural instability. These findings underscore the importance of ligand geometry in determining final framework properties. Collectively, this research establishes a generalizable approach to controlling MOF architecture through solvent modulation. By leveraging the dynamic interplay between flexible ligands and solvent environments, researchers can access diverse SBUs without altering metal or ligand identities, opening new avenues for designing functional materials with tailored porosity, stability, and electronic properties.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com