Ionic Liquid Assisted Exothermic Complexation of Trivalent Lanthanides with Fluorinated β Diketone: Multitechnique Approach with Theoretical Insight

The complexation of the betadiketone,1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedione (HFOD) was studied with trivalent lanthanide ions, viz. Nd3+, La3+, and Eu3+ in several methylimidazolium-based ionic liquids (Cnmim•NTf2, where, n = 4,6,8). In C6mim•NTf2, predominant formation of ML2+ and ML4- species was evidenced from the UV-vis absorption (Nd3+) as well as luminescence (Eu3+) spectral studies with log β2 ≈ 5.88 ± 0.04, log β4 ≈ 10.95 ± 0.06. The formation constants followed the trend C4mim•NTf2 > C6mim•NTf2 > C8mim•NTf2. The asymmetry factors for the ML2+ and ML4- species were found to be 1.2 and 1.59, respectively. The ML4- complex was found to have one primary coordination sphere water molecule with enhanced covalency between Eu3+ and O from HFOD (Judd Offelt constants Ω2 and Ω4 ≈ 17.2 and 2.35) compared to Eu3+aq, yet comparable to other β diketones. Complexation-induced temperature increase was confirmed by calorimetric measurements, indicating the exothermic complexation reaction (ΔHcomplexation ≈ -13.7 kJ mol-1), which is also spontaneous in nature (ΔG ≈ -68.1 kJ mol-1), with an enhancement in the entropy values. Due to complexation, the shifts in the peak positions (1686.66 cm-1, 1633.53 cm-1) associated with β diketone/ketone functional groups were evidenced. Density functional theory (DFT) calculation was performed to optimize the structural parameters including bond distance, bond angles, and energetics associated with the complexation.

Supramolecular chemistry of substituted cucurbit[n]urils

This review covers important advances in the field of substituted cucurbit[n]urils.

The lanthanide contraction effect and organic additives impact the coordination structures of lanthanide ions with symmetrical octamethyl-substituted cucurbit[6]uril ligands

Two facts, the lanthanide contraction effect and the “bridge” role of organic additives, impact the coordination structures of lanthanide ions with OMeQ[6] ligands.

Coordination and Supramolecular Assemblies of Fully Substituted Cyclopentanocucurbit[6]uril with Lanthanide Cations in the Presence of Tetrachlorozincate Anions, and Their Potential Applications

Coordination and supramolecular assemblies of a fully substituted cyclopentanocucurbit[6]uril (CyP₆Q[6]) with a series of lanthanide cations (Ln³⁺) have been investigated in the presence of tetrachlorozincate anion ([ZnCl₄]^2-). X-ray single-crystal diffraction analysis has revealed that the interaction of CyP₆Q[6] and a series of Ln³⁺cations unexpectedly results in the formation of at least seven different CyP₆Q[6]-based coordination complex adduct and supramolecular assemblies groups, including with (1) La³⁺, Ce³⁺cations; (2) Pr³⁺, Nd³⁺cations; (3) Eu³⁺, Gd³⁺, Tb³⁺, Dy³⁺ with P1̅ or P1 space group, in which CyP₆Q[6] molecules coordinate alternatively with Ln³⁺cations and form linear coordination polymers; (4) CyP₆Q[6] molecules interact alternatively with [Ho(H₂O)₈]³⁺ aqueous complexes and form linear supramolecular chains; CyP₆Q[6] molecules can assemble two different Ln³⁺ free porous supramolecular assemblies from CyP₆Q[6]-Ln(NO₃)₃-ZnCl₂-HCl systems, Ln = Tm, Yb, and Lu; however, no solid crystals were obtained from system containing Er³⁺cation. Thus, these differences could lead CyP₆Q[6] to be useful in not only the isolation of lighter lanthanides from their heavier lanthanides but also special selectivity for different volatile organic compounds.

Luminescent properties of heterotrinuclear 3d-4f complexes constructed from a naphthalenediol-based acyclic bis(salamo)-type ligand

Heterotrinuclear 3d-4f complexes with a naphthalenediol-based acyclic bis(salamo)-type ligand have been synthesized and structurally characterized. Spectral titrations clearly show that the heterotrinuclear complexes [Zn₂(L)La(OAc)₃] (1), [Zn₂(L)Ce(OAc)₃] (2) and [Zn₂(L)Dy(OAc)₃(CH₃OH)]·CH₂Cl₂ (3) are acquired by the substitution reaction of the obtained homotrinuclear Zn(II) complex with 1 equiv. of Ln(NO₃)₃ (Ln³⁺=La³⁺, Ce³⁺ and Dy³⁺). Two Zn(II) ions are penta- and hexa-coordinated with geometries of distorted tetragonal pyramid and octahedron. La(III) ion is deca-coordinated, adopting a distorted bicapped square antiprism geometry. Ce(III) ion is nona-coordinated with geometry of distorted capped square antiprism as well as Dy(III) ion. The different coordination modes of acetate ions in complexes 1, 2 and 3 lead to different coordination numbers of the lanthanide(III) ions. Furthermore, the structures and fluorescence properties have been discussed.

Host-guest complexation of di-cyclohexanocucurbit[6]uril and hexa-cyclohexanocucurbit[6]uril with alkyldiammonium ions: a comparative study

The host-guest complexation of symmetrical di-cyclohexanocucurbit[6]uril (Cy2Q[6]) and hexa-cyclohexanocucurbit[6]uril (Cy6Q[6]) with a series of alkyldiammonium ions (H(3+)N(CH(2))nNH(3+), n = 2-8) has been studied both in solution and in the gas phase. (1)H NMR data indicate that all alkyldiammonium ions have inclusion interactions with both hosts except for the ethanediammonium ion. In addition, if the alkyl chain of the alkyldiammonium ion is longer than n = 5 methylene groups, compressed conformation may occur, which depends on the cavity shape of the hosts and the length of the alkyl chain. Isothermal titration calorimetry (ITC) studies point out that the host-guest complexations of both hosts with the latter five alkyldiammonium ions are enthalpically driven. The comparison of the thermodynamic data reveals that the enthalpies of the van der Waals interactions contribute more to the host-guest complexation enthalpy than the ion-dipole interactions. The enthalpic gain arises from the van der Waals interactions and the reduction of entropy upon the host-guest complexation is strongly affected by the cavity shape of the host. Gas phase structures of long alkyldiammonium guests within both hosts are completely different from those in aqueous solution.

Cucurbit[n]uril-based coordination chemistry: from simple coordination complexes to novel poly-dimensional coordination polymers

Cucurbit[n]urils are a family of molecular container hosts bearing a rigid hydrophobic cavity and two identical carbonyl fringed portals. They have attracted much attention in supramolecular chemistry because of their superior molecular recognition properties in aqueous media. This review highlights the recent advances and challenges in the field of cucurbit[n]uril-based coordination chemistry. It not only presents progress in the knowledge of such macrocyclic compounds, which range from simple to complicated architectures, but also presents new routes of synthesis and their advantages in hybrid porous solids. The concept of structure "inducer" for their structural design to achieve predictable structures and controlled pores is described. The large pore sizes and hydrophobic cavities of these compounds that lead to unprecedented properties and potential applications are also discussed.