Selective binding and transport of highly hydrophilic anions is ubiquitous in nature, as anion binding proteins can differentiate between similar anions with over a million-fold efficiency. While comparable selectivity has occasionally been achieved for certain anions using small, artificial receptors, the selective binding of certain anions, such as sulfate in the presence of carbonate, remains a very challenging task. Nanojars of the formula [anion⊂{Cu(OH)(pz)} n ] 2− (pz = pyrazolate; n = 27–33) are totally selective for either CO 3 2− or SO 4 2− over anions such as NO 3 − , ClO 4 − , BF 4 − , Cl − , Br − and I − , but cannot differentiate between the two. We hypothesized that rigidification of the nanojar outer shell by tethering pairs of pyrazole moieties together will restrict the possible orientations of the OH hydrogen-bond donor groups in the anion-binding cavity of nanojars, similarly to anion-binding proteins, and will lead to selectivity. Indeed, by using either homoleptic or heteroleptic nanojars of the general formula [anion⊂Cu n (OH) n (L2–L6) y (pz) n −2 y ] 2− ( n = 26–31) based on a series of homologous ligands HpzCH 2 (CH 2 ) x CH 2 pzH ( x = 0–4; H 2 L2–H 2 L6), selectivity for carbonate (with L2 and with L4–L6/pz mixtures) or for sulfate (with L3) has been achieved. The synthesis of new ligands H 2 L3, H 2 L4 and H 2 L5, X-ray crystal structures of H 2 L4 and the tetrahydropyranyl-protected derivatives (THP) 2 L4 and (THP) 2 L5, synthesis and characterization by electrospray-ionization mass spectrometry (ESI-MS) of carbonate- and sulfate-nanojars derived from ligands H 2 L2–H 2 L6, as well as detailed selectivity studies for CO 3 2− vs. SO 4 2− using these novel nanojars are presented.
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Orthogonal, modular anion–cation and cation–anion self-assembly using pre-programmed anion binding sites
Subcomponent self-assembly relies on cation coordination whereas the roles of anions often only emerge during the assembly process. When sites for anions are instead pre-programmed, they have the potential to be used as orthogonal elements to build up structure in a predictable and modular way. We explore this idea by combining cation (M + ) and anion (X − ) binding sites together and show the orthogonal and modular build up of structure in a multi-ion assembly. Cation binding is based on a ligand (L) made by subcomponent metal-imine chemistry (M + = Cu + , Au + ) while the site for anion binding (X − = BF 4 − , ClO 4 − ) derives from the inner cavity of cyanostar (CS) macrocycles. The two sites are connected by imine condensation between a pyridyl-aldehyde and an aniline-modified cyanostar. The target assembly [LM-CS-X-CS-ML], + generates two terminal metal complexation sites (LM and ML) with one central anion-bridging site (X) defined by cyanostar dimerization. We showcase modular assembly by isolating intermediates when the primary structure-directing ions are paired with weakly coordinating counter ions. Cation-directed (Cu + ) or anion-bridged (BF 4 − ) intermediates can be isolated along either cation–anion or anion–cation pathways. Different products can also be prepared in a modular way using Au + and ClO 4 − . This is also the first use of gold( i ) in subcomponent self-assembly. Pre-programmed cation and anion binding sites combine with judicious selection of spectator ions to provide modular noncovalent syntheses of multi-component architectures.
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- Award ID(s):
- 2105848
- NSF-PAR ID:
- 10426873
- Date Published:
- Journal Name:
- Chemical Science
- Volume:
- 14
- Issue:
- 10
- ISSN:
- 2041-6520
- Page Range / eLocation ID:
- 2585 to 2595
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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null (Ed.)Imidazolium-based cations and the hexafluorophosphate anion are among the most commonly used ionic liquids (ILs). Yet, the nature and strength of the intrinsic cation–anion interactions, and how they influence the macroscopic properties of these ILs are still not well understood. Threshold collision-induced dissociation is utilized to determine the bond dissociation energies (BDEs) of the 2 : 1 clusters of 1-alkyl-3-methylimidazolium cations and the hexafluorophosphate anion, [2C n mim:PF 6 ] + . The cation, [C n mim] + , is varied across the series, 1-ethyl-3-methylimidazolium [C 2 mim] + , 1-butyl-3-methylimidazolium [C 4 mim] + , 1-hexyl-3-methylimidazolium [C 6 mim] + , 1-octyl-3-methylimidazolium [C 8 mim] + , to examine the structural and energetic effects of the size of the 1-alkyl substituent of the cation on the binding to [PF 6 ] − . Complementary electronic structure methods are employed for the [C n mim] + cations, (C n mim:PF 6 ) ion pairs, and [2C n mim:PF 6 ] + clusters to elucidate details of the cation–anion interactions and their impact on structure and energetics. Multiple levels of theory are benchmarked with the measured BDEs including B3LYP, B3LYP-GD3BJ, and M06-2X each with the 6-311+G(d,p) basis set for geometry optimizations and frequency analyses and the 6-311+G(2d,2p) basis set for energetic determinations. The modest structural variation among the [C n mim] + cations produces only minor structural changes and variation in the measured BDEs of the [2C n mim:PF 6 ] + clusters. Present results are compared to those previously reported for the analogous 1-alkyl-3-methylimidazolium tetrafluoroborate IL clusters to compare the effects of these anions on the nature and strength of the intrinsic binding interactions.more » « less
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P = 1 bar. The solubilities of the synthetic hydrotalcites, irrespective of their divalent‐trivalent cation partitioning ratio, scaled as CO32− < SO42− < OH−; in order of decreasing solubility. The type of anion, very slightly, affected the solubility with less than ±1 log unit of variation for [Mg/Al] = 2, and ±2 log units of variation for [Mg/Al] = 3. The solubilities of these phases were strongly correlated with that of gibbsite (Al(OH)3); such that activity of the [AlO2−] species wassolubility determining with increasing pH. The tabulated thermodynamic data were used to construct solid‐solution models for phases encompassing both cation distribution ratios and to calculate stable phase equilibria relevant to alkali‐activated slag (AAS) systems for diverse activator compositions.
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D2SC05121D
