Organometallic cavitands: Cation–π interactions and anion binding via π-metallation

Ultra-High Metal-Ion Selectivity Induced by Intramolecular Cation-π Interactions for the One-Pot Synthesis of Precise Heterometallic Architectures

Heterometallic supramolecules, known for their unique synergistic effects, have shown broad applications in photochemistry, host-guest chemistry, and catalysis. However, there are great challenges to precisely construct heterometallic supramolecules rather than a statistical mixture, due to the limited metal-ion selectivity of coordination units. In particular, heterometallic architectures precisely encoded with different metal ions usually fail to form in a one-pot method when only one type of coordinated motif exists due to its poor metal-ion selectivity. Herein, we propose an effective intramolecular cation-π (ICπ) strategy and successfully constructed the heterometallic supramolecule Zn2Cu4L34 by the one-pot self-assembly of tritopic terpyridyl ligand L3 with Zn(II) and Cu(II), following a clear self-assembly mechanism in which only thermodynamic dimers ZnL12 and Cu2L22 were constructed with model ligands L1, L2, Zn(II) and Cu(II) with perfect self-sorting and an ultra-high metal-selectivity feature. The successful construction of the heterometallic supramolecule Zn2Cu4L34, in which the definite sequence of metal ions Zn(II) and Cu(II) is encoded in the one-pot method, will offer a novel approach to precisely construct heterometallic architectures.

Rapid Cs+ Capture via Multiple Supramolecular Interactions in Anionic Metal-Organic Framework Isomers

Metal-organic frameworks (MOFs) provide an ideal platform for ion exchange due to their high porosity and structural designability; however, developing MOFs that have the essential characteristics for ion exchange remains a challenge. These crucial features include fast kinetics, selectivity, and stability. We present two anionic isomers, DGIST-2 (2D) and DGIST-3 (3D), comprising distinctly arranged 5-(1,8-naphthalimido)isophthalate ligands and In³⁺ cations. Interestingly, in protic solvents, DGIST-2 transforms into a hydrolytically stable crystalline phase, DGIST-2'. DGIST-2' and DGIST-3 exhibit rapid Cs⁺ adsorption kinetics, as well as high Cs⁺ affinity in the presence of competing cations. The mechanism for rapid and selective sorption is explored based on the results of single-crystal X-ray diffraction analysis of Cs⁺-incorporated DGIST-3. In Cs⁺-containing solutions, the loosely incorporated dimethylammonium countercation of the anionic framework is replaced by Cs⁺, which is held in the hydrophobic cavity by supramolecular ion-ion and cation-π interactions.

A multicolor and ratiometric fluorescent sensing platform for metal ions based on arene-metal-ion contact

Despite continuous and active development of fluorescent metal-ion probes, their molecular design for ratiometric detection is restricted by the limited choice of available sensing mechanisms. Here we present a multicolor and ratiometric fluorescent sensing platform for metal ions based on the interaction between the metal ion and the aromatic ring of a fluorophore (arene-metal-ion, AM, coordination). Our molecular design provided the probes possessing a 1,9-bis(2'-pyridyl)-2,5,8-triazanonane as a flexible metal ion binding unit attached to a tricyclic fluorophore. This architecture allows to sense various metal ions, such as Zn(II), Cu(II), Cd(II), Ag(I), and Hg(II) with emission red-shifts. We showed that this probe design is applicable to a series of tricyclic fluorophores, which allow ratiometric detection of the metal ions from the blue to the near-infrared wavelengths. X-ray crystallography and theoretical calculations indicate that the coordinated metal ion has van der Waals contact with the fluorophore, perturbing the dye's electronic structure and ring conformation to induce the emission red-shift. A set of the probes was useful for the differential sensing of eight metal ions in a one-pot single titration via principal component analysis. We also demonstrate that a xanthene fluorophore is applicable to the ratiometric imaging of metal ions under live-cell conditions.

A theoretical insight into non-covalent supramolecular interactions in the solid state structures of two octahedral iron(iii) complexes

The nature and characteristics of the C–H⋯π interactions that play an important role in crystal packing of two iron(iii) complexes have been discussed. The DFT calculations have been conducted to determine the interaction energies in these complexes.

A Co8 metallacycle stabilized by double anion–π interactions

The syntheses, crystal structures and magnetic studies of two new Co^II 2,2′-bipyrimidine bridged complexes stabilized by hydrogen bonding versus anion–π interactions are reported.

Supramolecular complexes formed by dimethoxypillar[5]arenes and imidazolium salts: a joint experimental and computational investigation

The stability of host–guest complexes formed by dimethoxypillar[5]arenes and imidazolium salts has been analyzed as a function of different structural features of the guest, using a combined approach of different techniques.

Structures of potassium calix[4]arene crown ether inclusion complexes and application in polymerization of rac-lactide

Reaction of 1,3-dipropoxy-p-tert-butyl-calix[4]arene (L(1)H2) with KN(SiMe3)2 afforded a one-dimensional (1D) chain complex [K2L(1)]n (1). Upon reaction with 1 equivalent 18-crown-6, complex 1 can convert to complex [K2(18-crown-6)L(1)] (2) which possesses a sandwich structure. Treatment of two calix[4]arene-crown ligands of 1,3-dihydroxy-p-tert-butyl-calix[4]arene-crown-5 (L(2)H2) and 1,2-dihydroxy-p-tert-butyl-calix[4]arene-crown-5 (L(3)H2) with KN(SiMe3)2 gave the dinuclear complex [K2L(2)] (3) and the mononuclear complex [K(THF)L(3)H] (4), respectively. Complexes 1-4 were all characterized by single-crystal X-ray diffraction techniques. The variable temperature (1)H NMR spectrum indicates there is a quick rotation equilibrium of the two phenoxy groups in complex 3. In addition, complexes 1-4 have been tested for the ring-opening polymerization (ROP) of rac-lactide and the results showed that complexes 2 and 3 are highly active for the ROP of rac-lactide. The obtained polymers displayed low dispersity values (Đ) and the molecular weights are close to the calculated ones. Furthermore, complexes 2 and 3 show moderate isoselectivities of Pm = 0.67 and Pm = 0.73, respectively.

Chiral Nanostructures from Helical Copolymer-Metal Complexes: Tunable Cation-π Interactions and Sergeants and Soldiers Effect

Poly(phenylacetylene) (PPA) copolymers containing (R)- or (S)-MPA as minor chiral pendant can be forced to selectively adopt the right- o left-handed helix, in the presence of small amounts of Na(+) or Ag(+) ("Sergeants and Soldiers Effect") by addition of a donor cosolvent. The helical sense depends exclusively on the chiral monomer/donor cosolvent ratio, and this allows a perfect on/off tuning of the helicity of the copolymer. When the amount of the donor cosolvent is low, the metal ion complex is stabilized by a cation-π interaction, which is selectively cleaved when the amount of cosolvent is higher. Macroscopically chiral nanospheres and nanotubes composed by helical copolymers with P or M helical sense are also described. Our results demonstrate that it is possible to obtain the two enantiomeric helical structures (P and M helicities) and the corresponding nanospheres and nanotubes from a single helical copolymer, by controlled activation/deactivation of the Sergeant and Soldiers Effect with a donor cosolvent.

Synthesis of Carboxylate Cp*Zr(IV) Species: Toward the Formation of Novel Metallocavitands

With the intent of generating metallocavitands isostructural to species [(CpZr)3(μ(3)-O)(μ(2)-OH)3(κO,O,μ(2)-O2C(R))3](+), the reaction of Cp*2ZrCl2 and Cp*ZrCl3 with phenylcarboxylic acids was carried out. Depending on the reaction conditions, five new complexes were obtained, which consisted of Cp*2ZrCl(κ(2)-OOCPh) (1), (Cp*ZrCl(κ(2)-OOCPh))2(μ-κ(2)-OOCPh)2 (2), [(Cp*Zr(κ(2)-OOCPh))2(μ-κ(2)-OOCPh)2(μ(2)-OH)2]·Et2O (3·Et2O), [[Cp*ZrCl2](μ-Cl)(μ-OH)(μ-O2CC6H5)[Cp*Zr]]2(μ-O2CC6H5)2 (4), and [Cp*ZrCl4][(Cp*Zr)3(κ2-OOC(C6H4Br)3(μ3-O)(μ2-Cl)2(μ2-OH)] [5](+)[Cp*ZrCl4](-). The structural characterization of the five complexes was carried out. Species 3·Et2O exhibits host-guest properties where the diethyl ether molecule is included in a cavity formed by two carboxylate moieties. The secondary interactions between the cavity and the diethyl ether molecule affect the structural parameters of the complex, as demonstrated be the comparison of the density functional theory models for 3 and 3·Et2O. Species 5 was shown to be isostructural to the [(CpZr)3(μ(3)-O)(μ(2)-OH)3(κO,O,μ(2)-O2C(R))3](+) metallocavitands.

The leading role of cation–π interactions in polymer chemistry: the control of the helical sense in solution

Cation–π interactions determine the helical sense adopted by a polyphenylacetylene bearing (R)-α-methoxy-α-phenylacetamide as a pendant group (poly-1).

Biomimetic cavity-based metal complexes

The biomimetic association of a metal ion with a cavity allows selective recognition, unusual redox properties and new reactivity patterns.

Survey on the complexation character of p-sulfonatocalix[n]arenes and Caffeic acid

In this work the inclusion complex formation of Caffeic acid (CA) with p-sulfonatocalix[n]arenes (SCXn, n=4, 6, 8) is reported aiming to improve the antioxidant activity, thermal stability and photostability properties of CA. Evidence for the formation was obtained using fluorescence spectroscopy, nuclear magnetic resonance spectroscopy (NMR), pulsed field gradient NMR (PFG-NMR), Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC) and scanning electron microphotographs (SEM). Experimental conditions including concentrations of SCXn and pH were investigated for the inclusion formation in detail. The results showed that CA was able to form inclusion complexes with SCXn in a molar ratio of 1:1, and the formation constants were varied with the pH conditions. NMR spectroscopy indicated that both the aromatic ring and the vinyl group of CA were partially covered by SCXn.

Synthesis and anion binding studies of o-phenylenevinylene-bridged tetrapyrrolic macrocycle as an expanded analogue of calix[4]pyrrole

An expanded analogue of calix[4]pyrrole with a flexible scaffold has been prepared; it acts as an effective anion receptor in organic media.

Enhanced anion binding from unusual coordination modes of bis(thiourea) ligands in platinum group metal complexes

Treatment of a range of bis(thiourea) ligands with inert organometallic transition-metal ions gives a number of novel complexes that exhibit unusual ligand binding modes and significantly enhanced anion binding ability. The ruthenium(II) complex [Ru(η(6)-p-cymene)(κS,S',N-L(3)-H)](+) (2b) possesses juxtaposed four- and seven-membered chelate rings and binds anions as both 1:1 and 2:1 host guest complexes. The pyridyl bis(thiourea) complex [Ru(η(6)-p-cymeme)(κS,S',N(py)-L(4))](2+) (4) binds anions in both 1:1 and 1:2 species, whereas the free ligand is ineffective because of intramolecular NH⋅⋅⋅N hydrogen bonding. Novel palladium(II) complexes with nine- and ten-membered chelate rings are also reported.

Temperature effect on the vibrational dynamics of cyclodextrin inclusion complexes: investigation by FTIR-ATR spectroscopy and numerical simulation

The vibrational dynamics of solid inclusion complexes of the nonsteroidal anti-inflammatory drug Ibuprofen (IBP) with beta-cyclodextrin (beta-CD) and methyl-beta-cyclodextrin (Me-beta-CD) has been investigated by using attenuated total reflection-Fourier transform infrared FTIR-ATR spectroscopy, in order to monitor the changes induced, as a consequence of complexation, on the vibrational spectrum of IBP, in the wavenumber range 600-4000 cm(-1). Quantum chemical calculations were performed on monomeric and dimeric structures of IBP, derived from symmetric hydrogen bonding of the two carboxylic groups, in order to unambiguously assign some characteristic IR bands in the IBP spectrum. The evolution in temperature from 250 to 340 K of the C horizontal lineO stretching vibration, described by a best-fit procedure, allowed us to extract the thermodynamic parameter DeltaH associated to the binding of IBP with betaCDs in the solid phase. By comparing these results, Me-beta-CD has been shown to be the most effective carrier for IBP.

Complex interactions of pillar[5]arene with paraquats and bis(pyridinium) derivatives

The complexation behavior of a series of paraquats (G1.2PF(6)-G5.2PF(6)) and bis(pyridinium) derivatives (G6.2PF(6)-G14.2PF(6)) with pillar[5]arene (P5A) host has been comprehensively investigated by (1)H NMR, ESI mass and UV-vis absorption spectroscopy. It is found that P5A forms 2 : 1 external complexes with N,N'-dialkyl-4,4'-bipyridiniums (G1-G4.2PF(6)); while it forms 1 : 1 pseudorotaxane-type inclusion complexes with methylene [-(CH(2))(n)-] linked bis(pyridinium) derivatives possessing appropriate chain lengths (n = 3-6, G7-G10.2PF(6)). Host-guest association constants in dimethyl sulfoxide (DMSO) were determined, indicating G7-G10.2PF(6) axles form stable [2]pseudorotaxanes with P5A wheel in this very high polarity solvent and 1,4-bis(pyridinium)butane (G8.2PF(6)) was the most suitable axle unit. Meanwhile, the nature of the substituents attached to 1,4-bis(pyridinium)butane dramatically affects the molecular recognition behavior. The introduction of pyridyls (G13.2PF(6)) increases not only the K(a) value (4.5 x 10(2) --> 7.4 x 10(2) M(-1)), but also the charge transfer (CT) absorption (colorless --> yellow). Furthermore, the solvent effects have also been investigated, showing they significantly influence the association strength during the course of host-guest complexation. Particularly, the K(a) value of P5A-G13.2PF(6) in 1 : 1 (v:v) acetone-d(6)/DMSO-d(6) is enhanced by a factor of 7.3 compared with pure DMSO-d6 (7.4 x 10(2) --> 5.4 x 10(3) M(-1)).

X-ray crystal analysis of a TASP: structural insights of a cavitein dimer

Cavitein Q4 is a template assembled synthetic protein designed for X-ray crystallographic analysis. It is based on a previous monomeric helical bundle cavitein (N1GG) that consists of four identical parallel helical peptides. Crystals that were grown in the presence of bromide ions were used to solve the initial phases via single-wavelength anomalous dispersion (SAD). A 1.4 A resolution data set was then refined starting with the SAD phases to provide the crystal structure of cavitein Q4. The crystal structure revealed cavitein Q4 as an asymmetric dimer, although the cavitein appears to be largely monomeric in solution. A comparative analysis is carried out to discern any intrinsic differences between Q4 and its parent cavitein N1GG. We present herein the first X-ray crystal structure of a TASP system and relate this structure to the solution data for both Q4 and its parent N1GG.