Anions as templates in coordination and supramolecular chemistry

Self-assembly of Ni(II) with a chiral ligand pair vs. mixture of the chiral ligand pair: structural features and recognition ability of Ni2L4 cages

The self-assembly of NiCl2 with a chiral bidentate ligand pair, (1R,2S)-(+)- and (1S,2R)-(-)-1-(nicotinamido)-2,3-dihydro-1H-inden-2-yl nicotinate (r,s-L and s,r-L) in a mixture of ethanol and dioxane, gives rise to stable crystals consisting of [2Cl@Ni2Cl2(s,r-L)4(H2O)2]·4C4H8O2·EtOH and [2Cl@Ni2Cl2(r,s-L)4(H2O)2]·4C4H8O2·EtOH chiral cages, respectively, with two encapsulated chloride anions in the cavities. The most interesting feature is that the self-assembly of NiCl2 with the mixture of r,s-L and s,r-L (1 : 1-1 : 4) produces crystals of thermodynamically stable achiral cages, [2Cl·2H2O@Ni2Cl2(s,r-L)2(r,s-L)2(H2O)2]·7C4H8O2, in the molar ratio range. Furthermore, the [2Cl@Ni2Cl2(s,r-L)4(H2O)2]·4C4H8O2·EtOH and [2Cl@Ni2Cl2(r,s-L)4(H2O)2]·4C4H8O2·EtOH chiral crystals can recognize the pairs of L-,D-tryptophan and L-,D-cysteine via cyclic voltammetry (CV) signals, in contrast to the [2Cl·2H2O@Ni2Cl2(s,r-L)2(r,s-L)2(H2O)2]·7C4H8O2 achiral crystal.

Interpenetration Phenomena via Anion Template Effects in Fe(II) and Co(II) Coordination Networks with a Bis-(1,2,4-triazole) Ligand

Seven new coordination networks, [Fe(tbbt)3](BF4)2 (1), [Co(tbbt)3](BF4)2 (2), [Fe(tbbt)3](ClO4)2 (3), [Co(tbbt)3](ClO4)2 (4), [Fe(NCS)2(tbbt)2] (5), [Co(NCS)2(tbbt)2] (6), and [Fe(H2O)2(tbbt)2]Br2·2H2O (7), were synthesized with the linker 1,1'-(trans-2-butene-1,4-diyl)bis-1,2,4-triazole (tbbt) and structurally investigated. The structure of complexes 1-4 is composed of three interpenetrating, symmetry-related 3D networks. Each individual 3D network forms a primitive, nearly cubic lattice (pcu) with BF4- or ClO4- anions present in the interstitial spaces. The structure of compounds 5 and 6 is composed of two-dimensional sql layers, which are parallel to each other in the AB stacking type. These layers are interpenetrated by one-dimensional chains, both having the same formula unit, [M(NCS)2(tbbt)2] (M = Fe, Co). The structure of compound 7 consists of parallel, two-dimensional sql layers in the ABCD stacking type. The interpenetration in 1-6 is not controlled by π-π-interactions between the triazole rings or C=C bonds, as could have been expected, but by (triazole)C-H⋯F4B, C-H⋯O4Cl, and C-H⋯SCN anion hydrogen bonds, which suggests a template effect of the respective non-coordinated or coordinated anion for the interpenetration. In 7, the (triazole)C-H⋯Br anion interactions are supplemented by O-H⋯O and O-H⋯Br hydrogen bonds involving the aqua ligand and crystal water molecules. It is evident that the coordinated and non-coordinated anions play an essential role in the formation of the networks and guide the interpenetration. All iron(II) coordination networks are colorless, off-white to yellow-orange, and have the metal ions in the high-spin state down to 77 K. Compound 5 stays in the high spin state even at temperatures down to 10 K.

Template-Directed Synthesis of Bivalent, Broad-Spectrum Hosts for Neuromuscular Blocking Agents*

We report on the synthesis of bivalent water-soluble calix[4]arene and calix[5]arene hosts, Super-sCx4 and Super-sCx5 as new broad-spectrum supramolecular binders of neuromuscular blocking agents (NMBAs). Synthesis was achieved using the target bisquaternary amine NMBAs as a template to link two highly anionic p-sulfonatocalixarene building blocks in aqueous solution. Bivalent anionic hosts Super-sCx4 and Super-sCx5 bind by engaging both quaternary amines present on a variety of NMBAs. We report low μM binding to structurally diverse alkyl, steroidal, curarine and benzylisoquinoline NMBAs with high selectivity over the neurotransmitter acetylcholine and a variety of other hydrophobic amines.

Unveiling anion-induced folding in tripodal imidazolium receptors by ion-mobility mass spectrometry

The anion-induced folding of tripodal imidazolium receptors has been investigated by NMR spectroscopy, electrospray ionization ion mobility mass spectrometry and DFT calculations. Such folding can be switched by anion release upon collision induced dissociation.

An overview of CO32−/HCO3− binding by aerial CO2 fixation within the self-assemblies of hydrogen-bond donor scaffolds

A comprehensive account of the F⁻/OH⁻-induced atmospheric CO₂ fixation as carbonate/bicarbonate anion(s) within the self-assemblies of artificial receptors are demonstrated in the highlight.

Dimensional Structures and Electrocatalytic Activities of Platinum(II)-Palladium(II)-Manganese(II) Coordination Polymers Controlled by Chloride versus Bromide

Here we report the synthesis and structural characterization of heterotrimetallic (Pt^II₂Pd^II₂Mn^II₂)_n coordination polymers that show different dimensionalities and electrocatalytic activities depending on chloride and bromide employed in the system. The reaction of the Pt^II₂Pd^II₂ tetranuclear complex [Pd₂Pt₂(NH₃)₄(d-pen)₄] (1), bearing free carboxylate groups, with Mn²⁺ in the presence of chloride produced the (Pt^II₂Pd^II₂Mn^II₂)_n coordination polymer [Mn₂Cl₂(H₂O)₆(1)]Cl₂ (2^Cl), in which the Pt^II₂Pd^II₂ units of 1 are linked by [MnCl(H₂O)₃]⁺ moieties in a 1:2 ratio to form a 2D sheetlike structure. The corresponding reaction in the presence of bromide also gave the (Pt^II₂Pd^II₂Mn^II₂)_n coordination polymer [Mn₂(H₂O)₆(1)]Br₄ (3^Br), but 3^Br adopted a 3D network structure via a 1:1 linkage of the Pt^II₂Pd^II₂ units with [Mn₂(H₂O)₆]⁴⁺ moieties. These complexes showed appreciably different electrocatalytic activities for H₂ evolution.

Helical Anion Foldamers in Solution

Using anions to induce molecular structure is a rapidly growing area of dynamic and switchable supramolecular chemistry. The emphasis of this review is on helical anion foldamers in solution, and many of the beautiful complexes described herein are accentuated by their crystal structures. Anion foldamers are defined as single- or multistrand complexes-often helical-that incorporate one or more anions. The review begins by discussing foldamer structure and nomenclature and follows with discourse on the anions which are employed. Recent advances in functional foldamers that bind a single anion are examined, including: induced chirality, stimuli-responsive dynamics, fluorescence changes, organocatalysis, anion transport, and halogen bonding. The review then inspects multianion foldamers, and this section is organized by the number of strands within the foldamer-from single- to triple-strand foldamers. Finally, the review is punctuated by recent hydrogen- and halogen-bonding triple-strand anion foldamers.

Highly Selective Anion Template Effect in the Synthesis of Constrained Pseudopeptidic Macrocyclic Cyclophanes

Herein, we report the synthesis of a novel family of constrained pseudopeptidic macrocyclic compounds containing the hexahydropyrrolo[3,4-f]isoindolocyclophane scaffold and involving four coupled substitution reactions in the macrocyclization process. Although the increase in the number of steps involved in the macrocyclization could lead to a larger number of possible side products, the optimization of the methodology and the study of the driving forces have made it possible to obtain the desired macrocycles in excellent yields. A thorough computational study has been carried out to understand the macrocyclization process, and the results obtained nicely agree with experimental data. Moreover, the bromide anion had a clear catalytic template effect in the macrocyclization reaction, and surprisingly, the chloride anion had a negative template effect in opposition to the results obtained for analogous macrocycles. The parameters responsible for the specific kinetic template effect observed have been studied in detail.

Ligand-Directed Template Assembly for the Construction of Gigantic Molybdenum Blue Wheels

Template-mediated synthesis is a powerful approach to build a variety of functional materials and complex supramolecular systems. However, the systematic study of how templates structurally evolve from basic building blocks, and then affect the templated self-assembly, is critical to understanding and utilizing the underlying mechanism, to work towards designed assembly. Here we describe the templated self-assembly of a series of gigantic Mo Blue (MB) clusters 1-4 using l-ornithine as a structure-directing ligand. We show that by using l-ornithine as a structure director, we can form new template⊂host assemblies. Based on the structural relationship between encapsulated templates of {Mo8 } (1), {Mo17 } (2) and {Mo36 } (4), a pathway of the structural evolution of templates is proposed. This provides insight into how gigantic Mo Blue cluster rings form and could lead to full control over the designed assembly of gigantic Mo-blue rings.

cis- and trans-9,10-di(1H-imidazol-1-yl)-anthracene based coordination polymers of ZnII and CdII: synthesis, crystal structures and luminescence properties

New luminescent coordination polymers of anthracene with Zn^II and Cd^II were developed for detection of traces of nitro explosives.

The conformational behavior of multivalent tris(imidazolium)cyclophanes in the hybrids with metal (pseudo)halides or polyoxometalates

Three 3D imidazole or benzimidazole-bearing cages as trivalent cationic templates react with metal (pseudo)halides or polyoxometalates to obtain a series of different organic–inorganic hybrids in which the cages exhibit breathing behavior of expansion and contraction.

Co-crystallization of 1,3,5-trifluoro-2,4,6-triiodobenzene (1,3,5-TFTIB) with a variety of Lewis bases through halogen-bonding interactions

Co-crystallization of 1,3,5-trifluoro-2,4,6-triiodobenzene (1,3,5-TFTIB) with a variety of halogen-bonding acceptors.

Post-synthetic ion-exchange process in nanoporous metal–organic frameworks; an effective way for modulating their structures and properties

In this review paper, we considered all of the reports on the ion-exchange process which occur in the pores of MOFs. A comparison between MOFs before and after-exchange process and their applications were addressed.

Self-Templating and In Situ Assembly of a Cubic Cluster-of-Clusters Architecture Based on a {Mo24 Fe12 } Inorganic Macrocycle

Engineering self‐templating inorganic architectures is critical for the development of bottom‐up approaches to nanoscience, but systems with a hierarchy of templates are elusive. Herein we describe that the cluster‐anion‐templated (CAT) assembly of a {CAT}⊂{Mo₂₄Fe₁₂} macrocycle forms a giant ca. 220 nm³ unit cell containing 16 macrocycles clustered into eight face‐shared tetrahedral cluster‐of‐clusters assemblies. We show that {CAT}⊂{Mo₂₄Fe₁₂} with different CATs gives the compounds 1–4 for CAT=Anderson {FeMo₆} (1), Keggin {PMo₁₂} (2), Dawson {P₂W₁₈} (3), and {Mo₁₂O₃₆(HPO₃)₂} (4) polyoxometalates. “Template‐free” assembly can be achieved, whereby the macrocycle components can also form a template in situ allowing template to macrocycle to superstructure formation and the ability to exchange the templates. Furthermore, the transformation of template clusters within the inorganic macrocycle {Mo₂₄Fe₁₂} allows the self‐generation of an uncapped {Mo₁₂O₃₆(HPO₃)₂} in compound 4.

Host-Guest Chemistry: Oxoanion Recognition Based on Combined Charge-Assisted C-H or Halogen-Bonding Interactions and Anion⋅⋅⋅Anion Interactions Mediated by Hydrogen Bonds

Several bis-triazolium-based receptors have been synthesized and their anion-recognition capabilities have been studied. The central chiral 1,1'-bi-2-naphthol (BINOL) core features either two aryl or ferrocenyl end-capped side arms with central halogen- or hydrogen-bonding triazolium receptors. NMR spectroscopic data indicate the simultaneous occurrence of several charge-assisted aliphatic and heteroaromatic C-H noncovalent interactions and combinations of C-H hydrogen and halogen bonding. The receptors are able to selectively interact with HP2 O7 (3-) , H2 PO4 (-) , and SO4 (2-) anions, and the value of the association constant follows the sequence: HP2 O7 (3-) >SO4 (2-) >H2 PO4 (-) . The ferrocenyl end-capped 7(2+) ⋅2 BF4 (-) receptor allows recognition and differentiation of H2 PO4 (-) and HP2 O7 (3-) anions by using different channels: H2 PO4 (-) is selectively detected through absorption and emission methods and HP2 O7 (3-) by using electrochemical techniques. Significant structural results are the observation of an anion⋅⋅⋅anion interaction in the solid state (2:2 complex, 6(2+) ⋅[H2 P2 O7 ](2-) ), and a short C-I⋅⋅⋅O contact is observed in the structure of the complex [8(2+) ][SO4 ]0.5 [BF4 ].

Metallosupramolecular Chemistry of AgI Complexes with Azobis(2-pyridine) and its Derivatives

Reactions of three azobis(2-pyridines) with silver salts lead to 1D coordination polymers whose structures have been determined by single crystal X-ray crystallography. The azobis(2-pyridines) consistently act as di-bidentate ligands that bridge silver atoms separated by distances ranging from 5.49 to 5.82 Å. Two of the coordination polymers consist of chains in which consecutive bridging ligands are orthogonally oriented. The other polymer has a considerably more complicated structure due to the more intimate involvement of the trifluoroacetate counteranions, which also act as bridges between silver centres.

Anion induced structural transformation in silver-(3,6-dimethoxy-1,2,4,5-tetrazine) coordination polymers under mechanochemical conditions

Mechanochemical processes allow the 1D chain of [Ag(dmotz)(CF₃SO₃)]_n to easily convert to a 2D grid network of {[Ag(dmotz)₂](ClO₄)}_n in the presence of [ClO₄]⁻.

Phosphate binding by a novel Zn(II) complex featuring a trans-1,2-diaminocyclohexane ligand. Effective anion recognition in water

In this work we have investigated the binding properties of a new synthetic receptor for phosphate anions that combines metal ion coordination with electrostatic and H-bonding interactions. The described receptor is obtained by assembling an iminodiacetic (IDA) fragment, as a Zn(II) binding site, with a polyamine macrocyclic portion containing two trans-1,2-diaminocyclohexane (DAC) units and a pyrrole ring, as a cationic binding site, into an adaptive structure appropriately spanning the length of di- and tridentate phosphates. Potentiometric measurements together with (1)H and (31)P NMR investigation showed that, in a wide pH range including values of physiological interest, the Zn(II) complex of the receptor binds di- and triphosphates, such as ADP, ATP, pyrophosphate (PP) and triphosphate (TP), far better than monophosphate (MP), and that TP is poorly bound by methyliminodiacetate (MIDA) as a model for the Zn(II) binding site. Besides the excellent selectivity over other phosphates, the affinity for TP is the largest reported to date for Zn(II) complexes in water.