Search

p-tert-Butylcalix[4]arene is a bowl-shaped molecule capable of forming a range of polynuclear metal clusters under different experimental conditions. p-tert-Butylcalix[8]arene (TBC[8]) is a significantly more flexible analogue that has previously been shown to form mono- and binuclear lanthanide (Ln) metal complexes. The latter (cluster) motif is commonly observed and involves the calixarene adopting a near double-cone conformation, features of which suggested that it may be exploited as a type of assembly node in the formation of larger polynuclear lanthanide clusters. Variation in the experimental conditions employed for this system provides access to Ln(1), Ln(2), Ln(4), Ln(5), Ln(6), Ln(7) and Ln(8) complexes, with all polymetallic clusters containing the common binuclear lanthanide fragment. Closer inspection of the structures of the polymetallic clusters reveals that all but one (Ln(8)) are in fact based on metal octahedra or the building blocks of octahedra, with the identity and size of the final product dependent upon the basicity of the solution and the deprotonation level of the TBC[8] ligand. This demonstrates both the versatility of the ligand towards incorporation of additional metal centres, and the associated implications for tailoring the magnetic properties of the resulting assemblies in which lanthanide centres may be interchanged., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In the cone conformation calix[4]arenes possess lower-rim polyphenolic pockets that are ideal for the complexation of various transition-metal centres. Reaction of these molecules with manganese salts in the presence of an appropriate base (and in some cases co-ligand) results in the formation of a family of calixarene-supported [Mn(III)(2)Mn(II)(2)] clusters that behave as single-molecule magnets (SMMs). Variation in the alkyl groups present at the upper-rim of the cone allows for the expression of a degree of control over the self-assembly of these SMM building blocks, whilst retaining the general magnetic properties. The presence of various different ligands around the periphery of the magnetic core has some effect over the extended self-assembly of these SMMs., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The use of methylene-bridged calix[4]arenes in 3d/4f chemistry produces a family of clusters of general formula [Mn(III)(4)Ln(III)(4)(OH)(4)(C4)(4)(NO(3))(2)(DMF)(6)(H(2)O)(6)](OH)(2) (where C4 = calix[4]arene; Ln = Gd (1), Tb (2), Dy (3)). The molecular structure describes a square of Ln(III) ions housed within a square of Mn(III) ions. Magnetic studies reveal that 1 has a large number of molecular spin states that are populated even at the lowest investigated temperatures, while the ferromagnetic limit S = 22 is being approached only at the highest applied fields. This, combined with the high magnetic isotropy, makes the complex an excellent magnetic refrigerant for low-temperature applications. Replacement of the isotropic Gd(III) ions with the anisotropic Tb(III) and Dy(III) ions "switches" the magnetic properties of the cluster so that 2 and 3 behave as low-temperature molecular magnets, displaying slow relaxation of the magnetization.

Three interpenetrated metal-organic supramolecular isomers were synthesised using a flexible tetrahedral organic linker and Zn(2) clusters that sorb CO(2) preferably over N(2), H(2) and methane at room temperature.

The synthesis of a series of iron and ruthenium complexes with the new ligand PP(i)(3) (1) P(CH(2)CH(2)P(i)Pr(2))(3) is described. The iron(0) and ruthenium(0) dinitrogen complexes Fe(N(2))(PP(i)(3)) (4) and Ru(N(2))(PP(i)(3)) (5) were synthesized by treatment of the iron(II) and ruthenium(II) cationic species [FeCl(PP(i)(3))](+) (2) and [RuCl(PP(i)(3))](+) (3) with potassium graphite under a nitrogen atmosphere. The cationic dinitrogen species [Fe(N(2))H(PP(i)(3))](+) (6) and [Ru(N(2))H(PP(i)(3))](+) (7) were prepared by treatment of 4 and 5, respectively, with 1 equiv of a weak organic acid. Complexes 2.[BPh(4)], 3.[BPh(4)], 4, 5, and 6.[BF(4)] were characterized by X-ray crystallography. The structural characterization of 5 is the first report for a ruthenium(0) dinitrogen complex.

Metal ions or ion pairs (silver nitrate shown) are transported to the interior of metal-organic pyrogallol[4]arene nanocapsules via aqueous "gates". This transport has been studied by X-ray crystallography and shows the affinity of the ions to reside deep in the polyaromatic regions of the assemblies.

A breathing 2-fold interpenetrated microporous metal-organic framework was synthesized with a flexible tetrahedral organic linker and Zn(2) clusters that sorb CO(2) preferably over N(2) and H(2).

Pyrogallol[4]arenes form stable hydrogen-bonded nanocapsules that have unique properties that may make them suitable for diverse applications, such as catalysts and molecular transporters. Little is known about the behavior of the interior of these new materials in solution, and by using the solvent-dependent properties of 1-(9-anthryl)-3-(4-dimethylaniline) propane (ADMA), the inner phase properties of the hexamers are investigated. Steady-state and dynamic spectrofluorometric results are in agreement, are consistent with solid-state studies, and indicate that the majority of ADMA is sequestered in an extended conformation with the crystallization solvent. The conformational flexibility of ADMA is attributed to lower capsule occupancies ( approximately 50%, i.e., 1 molecule per 2 capsules, one occupied and one empty) relative to our previous study with pyrene butyric acid (occupancy of 150%, i.e., 1.5 molecules per capsule) in which the probe was restricted within a nanocapsule. The nature of the encapsulated ADMA complexes are found to change with time, as there is either fluorophore leaching from the capsule or endo-exo-capsule solvent exchange. However, the choice of crystallizing solvent (ethyl acetate or acetonitrile) and PgC(n) alkyl tail (C(6) or C(10)) does not influence experimental outcomes. These research findings give a better understanding of the encapsulation versatility of these unique supramolecular assemblies and the protective nanopockets that can exist for guest molecules.

Under various conditions, water molecules dramatically affect a number of solid-state C-alkylpyrogallol[4]arene assemblies. In the absence of water, hydrogen-bonded hexameric capsules are formed for the C-butyl, pentyl, hexyl, and heptyl pyrogallol[4]arenes. Introduction of water to acetonitrile solutions containing C-propyl-C-octylpyrogallol[4]arenes resulted in the formation of markedly different bilayer structures and the structural identification of two new dimer-type motifs.

Diffusion-ordered (1)H NMR spectroscopy techniques have been used to determine the binding strength of p-sulfonatocalix[4]arene (SO(3)[4]) towards a number of charged crown ether species in aqueous conditions. For several (doubly) charged (di)azacrown ethers, all were bound by SO(3)[4] either well or very well with binding constants between 5.1 x 10(2)-9.9 x 10(5) M(-1). These results correlate with, and thus explain the phenomenon of rapid capture of azacrown ethers in molecular capsules based on p-sulfonatocalix[4]arene and lanthanide metals. Similarly, the formation of "Russian doll" superanions in the solution phase is also elucidated. These superanions have been shown to selectively crystallise particular polynuclear aquated metal ions from mixtures in the aqueous phase. Neutral [18]crown-6 is not bound by p-sulfonatocalix[4]arene and displays a binding constant of 0 M(-1). When sodium [18]crown-6 is examined in a similar fashion, binding by SO(3)[4] is observed in solution with K(a) approximately 3.1 x 10(3) M(-1).

Control over the conformational flexibility of p-sulfonatocalix[6]arene in the solid state is possible in the presence of varied stoichiometric amounts of [18]crown-6 and selected lanthanide(III) chlorides. Complexes 1 and 2 have the calixarene in the elusive up-up double cone conformation, whilst complex 3 has the calixarene in the centrosymmetric up-down double partial cone conformation, whereby it acts as a divergent receptor. Complex 1 has a double molecular capsule arrangement which is composed of two p-sulfonatocalix[6]arenes shrouding two [18]crown-6 molecules, also with both coordinated and homoleptic aquated lanthanide ions around the hydrophilic sulfonate rims of the calixarenes. Complex 2 has a ferris wheel arrangement with one lanthanide metal centre coordinated to a sulfonate group and another coordinated to the crown ether whilst tethered to a sulfonate group of the calixarene. Complex 3 forms from a solution with large excess of [18]crown-6, and possesses a crown ether molecule in each of the partial cones and has homoleptic aquated lanthanide ions involved in a complicated hydrogen-bonding regime within the extended structure.

Treating p-sulfonatocalix[4]arene with lanthanide ions, Ln3+ (Ln = Ce, Nd, Sm and Eu), in the presence of [2.2.2]cryptand results in a 2-D bi-layer coordination polymer with axially elongated diprotonated cryptand in the cavity of two p-sulfonatocalix[4]arenes.