Organic–inorganic hybrid materials: Metallacalixarenes. Synthesis and applications

Self-Assembly of a Purely Organic Bowl in Water via Acylhydrazone Formation

A bowl-shaped molecule can be self-assembled by condensing a triscationic hexaaldehyde compound and three equiv. of a dihydrazide linkers in pure water. The molecular bowl is thus composed of a triscationic π-electron deficient platform, as well as a hexagonal rim that contains six acylhydrazone functions. When the counteranions are chloride, the solid-state structure reveals that this molecular bowl undergoes dimerization via N-H···Cl hydrogen bonds, forming a cage-like dimer with a huge inner cavity. This molecular bowl can employ its cavity to accommodate a hydrophobic guest, namely 1-adamantanecarboxylic acid in aqueous media.

Rhenium(I)-Based Heteroleptic Pentagonal Toroid-Shaped Metallocavitands: Self-Assembly and Molecular Recognition Studies

A family of neutral, heteroleptic, dinuclear M₂LL'-type pentagonal toroid-shaped metallomacrocycles (1-8) were synthesized using flexible ditopic N donors (Lⁿ = L¹-L²), rigid bis-chelating ligands (H₂-L' = H₂-E), and Re₂(CO)₁₀ in a one-pot solvothermal self-assembly approach. The ligands and the metallomacrocycles were characterized using ATR-IR, electrospray ionization mass spectrometry, nuclear magnetic resonance, ultraviolet-visible, and emission spectroscopy methods. The molecular structures of 1, 2, 4, 6, and 7 were confirmed by an X-ray diffraction study and are similar to those of calix[5]arene. The cyclic inner cavities of the metallomacrocycles accommodate toluene/mesitylene/acetone/chlorobenzene as guest molecules that are stabilized by cumulative C-H···π and π···π interactions with the cyclic framework of metallomacrocycle. The photophysical properties of the ligands and the metallomacrocycles were studied. The host-guest recognition properties of metallocavitands 1, 2, 7, and 8 as a model host with phenol and nitrobenzene derivatives as guest molecules were studied by emission spectroscopy methods.

Calix[4]arene-Analogous Technetium Supramolecules

Calix[4]arene-analogous technetium supramolecules (1 and 2) were assembled using (NBu₄)[Tc₂(μ-Cl)₃(CO)₆] and neutral flexible bidentate nitrogen-donor ligands (L¹ and L²) consisting of four arene units covalently joined via methylene units. The neutral homoleptic technetium macrocycles adopt a partial cone/cone-shaped conformation in the solid state. These supramolecules are the first example of fac-[Tc(CO)₃]⁺ core-based metallocalix[4]arenes and second example of fac-[Tc(CO)₃]⁺ core-based metallomacrocycles. Structurally similar fac-[Re(CO)₃]⁺ core-based macrocycles (3 and 4) were also prepared using [Re(CO)₅X] (where X = Cl or Br) and L¹ or L². The products were characterized spectroscopically and by X-ray analysis.

Two Giant Calixarene-Like Polyoxoniobate Nanocups {Cu12 Nb120 } and {Cd16 Nb128 } Built from Mixed Macrocyclic Cluster Motifs

Cup-shaped molecules are of great interest due to their appealing architectures and properties. Compared with widely studied calixarenes, polyoxometalate-based cup-shaped molecules currently remain a virgin land waiting for exploration. In this work, we report the first discovery of two giant cup-shaped inorganic-organic hybrid polyoxoniobates (PONbs) of {Cu₁₂ Nb₁₂₀ } and {Cd₁₆ Nb₁₂₈ }. The former integrates three tricyclic Nb₂₄ clusters and a hexacyclic Nb₄₈ cluster into a cup-shaped molecule via a Cu₁₂ metallacalixarene, while the latter unifies two tricyclic Nb₂₄ clusters and a brand-new pentacyclic Nb₄₀ cluster into another cup-shaped molecule via a hybrid Cd₁₆ unit. With 132 and 144 metal centers, {Cu₁₂ Nb₁₂₀ } and {Cd₁₆ Nb₁₂₈ } show the largest two inorganic-organic hybrid PONbs known to date.

Recent progress to construct calixarene-based polymers using covalent bonds: synthesis and applications

The combination of supramolecular chemistry and polymer sciences creates a great possibility to afford calixarene-based polymers offering unique features and applications. The enhancement of calixarene's versatility in this manner has made chemists better able to achieve different objectives in host-guest chemistry. The calixarene-based polymers can be divided into covalent polymers and supramolecular polymers regarding the interactions. Although there are several studies available on the calixarene-based supramolecular polymers, there is a paucity of studies on the calixarene-based covalent polymers. In this paper, the most recent developments and applications of the calixarene-based covalent polymers in the last two decades have been reviewed. We have particularly focused on the polymers, including those where the calixarene molecules have been used as macromonomers and polymerize through covalent bonds. Moreover, covalent polymers or solid supports functionalized with calixarenes are highlighted as well.

Polyoxometalate-Incorporated Metallacalixarene@Graphene Composite Electrodes for High-Performance Supercapacitors

Composites of polyoxometalate (POM)/metallacalixarene/graphene-based electrode materials not only integrate the superiority of the individual components perfectly but also ameliorate the demerits to some extent, providing a promising route to approach high-performance supercapacitors. Herein, first, we report the preparations, structures, and electrochemical performance of two fascinating POM-incorporated metallacalixarene compounds [Ag₅(C₂H₂N₃)₆][H₅ ⊂ SiMo₁₂O₄₀] (1) and [Ag₅(C₂H₂N₃)₆][H₅ ⊂ SiW₁₂O₄₀] (2); (C₂H₂N₃ = 1 H-1,2,4-triazole). Single-crystal X-ray diffraction analyses illustrated that both 1 and 2 possess intriguing POM-sandwiched metallacalix[6]arene frameworks. Nevertheless, our investigations, including the electrochemical cyclic voltammetry, galvanostatic charge-discharge tests, and electrochemical impedance spectroscopy, reveal that the oxidation ability of the Keggin ions is a primary effect in electrochemical performance of these POM-incorporated metallacalixarene compounds. Namely, the electrodes containing Mo as metal atoms in the Keggin POM shows much higher capacitance than the corresponding W-containing ones. Moreover, compound 1@graphene oxide (GO) composite electrodes are fabricated and systematically explored for their supercapacitor performance. Thanks to the synergetic effects of GO and POM-incorporated metallacalixarenes, the compound 1@15%GO-based electrode exhibits the highest specific capacitance of up to 230.2 F g^-1 (current density equal to 0.5 A g^-1), which is superior to majority of the reported POM-based electrode materials.

Self-Assembly of Aluminum- and Gallium-Based meso-Metallaporphyrins

The molecular meso-metallaporphyrin has been obtained from the reaction of AlMe₃ with the bulky 4,5-(Ph₂(HO)C)₂-1,2,3-triazole (1). The presence of Al-Me groups coordinated to the triazole rings creates three different stereoisomers that were identified by single-crystal X-ray diffraction. Further studies revealed that, for steric reasons, only one of the two main stereoisomers is active in the polymerization of ε-caprolactone. When GaMe₃ is used instead of AlMe₃, a trimetallic species is formed instead of the meso-metallaporphyrin pointing to a metal-directed self-assembly. On the other hand, the reaction of the monolithium salt [{Li(THF)₂}{κ²- N, N'-4,5-(Ph₂(HO)C)-1,2,3-triazole}]₂ (2; THF = tetrahydrofuran) with MCl₃ (M = Al, Ga) yields meso-metallaporphyrin species with a lithium atom in the center of the metallacycle. While the gallium derivative is rather stable in solution, the aluminum analogue decomposes rapidly. In the solid state, continuous cationic columns running throughout the whole crystal are formed from alternating Li⊂[M]₄ (M = Al, Ga) meso-metallaporphyrin and [Li(THF)₄]⁺ cations. Density functional theory calculations determined that the weak Cl···H, H···H, N···H, and Cl···O interactions with a total interaction energy of -38.6 kcal·mol^-1 are responsible for this unusual packing.

Rhenium(i) based irregular pentagonal-shaped metallacavitands

Neutral ditopic flexible N-donor ligands (Ln = bis(4-(naphtho[2,3-d]imidazol-1-ylmethyl)phenyl)methane, L1 bis(4-(benzimidazol-1-ylmethyl)phenyl)methane, L2 or bis(4-(2-nonylbenzimidazol-1-ylmethyl)phenyl)methane, L3) possessing a bis(4-methylphenyl)methane spacer with two imidazolyl donor units were designed and synthesized. The ligands were utilized to develop metallacavitands analogous to irregular pentagonal-shaped metallacavitands with larger cavities. The metallacavitands 1-4 were assembled from Re2(CO)10, a rigid bis-chelating donor (1,4-dihydroxy-9,10-anthraquinone or chloranilic acid) and Lnvia a solvothermal approach. The ligands and the metallacavitands were characterized by analytical and spectroscopic methods. The molecular structures of 1 and 4 were further confirmed by single crystal X-ray diffraction analysis which revealed that a toluene molecule resides in the hydrophobic cavity. Ln and 1-4 are emissive in DMSO at room temperature. The internal cavity of the metallacavitand acts as a host for aromatic guest molecules. The host-guest interaction properties of 1 with anthracene, naphthalene, nitrobenzene, 2-nitrotoluene, 4-nitrotoluene and 2,4-dinitrotoluene were studied by an emission spectroscopic method.

Spheroid Metallacycles and Metallocavitands with Calixarene- and/or Cleft-Shaped Receptors on the Surface

Flexible hexatopic ligands, 1,2,3,4,5,6-hexakis(1H-naphtho[2,3-d]imidazol-1-ylmethyl)benzene (L(2)) and 1,2,3,4,5,6-hexakis(4,5-diphenylimidazol-1-ylmethyl)benzene (L(3)), containing six neutral naphthanoimidazolyl and 4,5-diphenylimidazolyl N donors were synthesized and used to assemble M6L6L'-type [M = Re(CO)3, L = anionic angular rigid NN donors, and L' = flexible hexatopic N donors] spheroid metallacycles. These molecules with a diameter of ∼17 Å were obtained from Re2(CO)10, H-L (imidazole, benzimidazole, and naphthanoimidazole), and L' [1,2,3,4,5,6-hexakis(benzimidazol-1-ylmethyl)benzene (L(1)), L(2), and L(3)] in a one-step process. Ligands L(2) and L(3) were characterized by elemental analysis, electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS), and (1)H NMR spectroscopy. Metallacycles 1-5 were characterized by elemental analysis, ESI-TOF-MS, Fourier transform infrared spectroscopy, and single-crystal X-ray diffraction analysis. Molecules 1, 2, and 4 can be considered as metallocavitands and contain multiple solvent-accessible receptors, i.e., two metallocalix[3]arene units and six/four calix[4]arene-/cleft-shaped receptors, on the surface. Guests such as acetone molecules could be accommodated in the calix[4]arene/cleft-shaped receptor of the metallocavitands.

Rhenium(I)-based bridgeless double metallocalix[4]arenes

Bridgeless double metallocalix[4]arenes possessing two orthogonally arranged dinuclear cavitands were obtained from a Re2(CO)10, rigid bis-chelating OO donor (H2-L), and a flexible bis-ditopic NN donor (L') by a one-pot approach.

Synthesis and characterization of bis (acetylacetonato κ-O, O′) [zinc(ii)/copper(ii)] hybrid organic–inorganic complexes as solid metal organic precursors

We have synthesized novel metal organic hybrid mixed compounds of bis (acetylacetonato κ-O, O′) [zinc(ii)/copper(ii)].

A ladder-type coordination polymer constructed from two macrocyclic units – calix[4]arene tetracarboxylate and azamacrocyclic nickel(ii) complex

Spatially-separated polar channels and non-polar voids were shown to coexist in the crystal of a new type of coordination polymer formed by a hexaazamacrocyclic nickel(ii) cation and a lower rim substituted calix[4]arene tetracarboxylate trianion.

Novel organic–inorganic hybrid soft xerogels with lanthanide complexes through an ionic liquid linkage

Functional hybrid soft materials [Ln(L)₄]⁻IM⁺–Al/Ti are prepared by sol–gel derived hosts based on Ti–O or Al–O groups, with an exchange reaction of the ionic liquid 3-(5-carboxy-propyl)-1-methyl-imidazolium bromide and lanthanide complexes.