Two isostructural octanuclear {(LnIII4CoII4)(C8A)2} compounds (Ln = Dy, Er; H8C8A = p-tert-butylcalix[8]arene) are synthesized under solvothermal conditions for magnetic study. For comparison, an yttrium compound, having a similar structure, except for some coordinated DEF molecules replaced by water molecules, is obtained. These three compounds are featured with a sandwich-like motif in which the heterometallic {LnIII4Co4II} square-antiprismatic cluster is sandwiched between two calix[8]arene molecules in double-cone conformation. Magnetic measurements reveal that the {DyIII4CoII4} compound exhibits single-molecule magnetic behavior.

•The mixtures of HEHAPP and D2EHPA exhibit a remarkable synergistic effect toward the Lu(III) extraction.•Maximum synergistic effect was obtained with a HEHAPP/D2EHPA molar ratio being of 1:1.•The separation performance for heavy REs was comparable with those of other synergistic systems.•The synergistic complex of Lu(III) was determined to be LuH4Cl2A3B2.A binary mixture of α-aminophosphonic acid extractant 2-ethylhexyl-3-(2-ethylhexylamino)pentan-3-yl-phosphonic acid (HEHAPP, H2A2) and di-(2-ethylhexyl) phosphoric acid (D2EHPA, H2B2) in n-heptane was employed for the extraction and separation of rare earths (REs) from chloride medium. A remarkable synergistic effect was observed in the Lu(III) extraction by the mixture. The extracted species of Lu(III) was determined as LuH4Cl2A3B2. The separation factors of adjacent heavy REs, i.e. SFEr/Ho, SFTm/Er, SFYb/Tm and SFLu/Yb, were of 1.45, 2.58, 2.77 and 1.77, which were much higher than those for other reported synergistic systems, suggesting that the mixture of HEHAPP and D2EHPA is a potential synergistic extraction system for the separation of heavy REs.

•An α-aminophosphonate extractant was synthesized to extract and separate cerium(IV) from thorium and trivalent rare earths.•The extractant can be used to selectively recover cerium in sulfate medium.•The stoichiometry of the extracted species was determined.•Thermodynamic functions were calculated for the extraction reaction.A novel extractant, di (2-ethylhexyl) (2-((2-ethylhexyl) amino) propan-2-yl) phosphonate (DEHAPP, abbreviated as B), was synthesized for the selective extraction of Ce(IV) in sulfate medium. The effect of contact time, the H2SO4 concentration, the DEHAPP concentration and temperature on the Ce(IV) extraction were studied systematically. DEHAPP exhibits a good extraction ability towards Ce(IV) when compared with other neutral organophosphorus extractants such as Cyanex 923, Cyanex 925 and DEHEHP. The extraction equilibrium constants and thermodynamic parameters (ΔG, ΔH and ΔS) were calculated. The extraction reaction of Ce(IV) is an endothermic process. The extracted complexes were determined to be H2SO4·B(org) and Ce(HSO4)2SO4·2B(org). A extraction process to selectively recover Ce(IV) from bastnaesite leaching was proposed, by which the purity of cerium product reached 99.5% with a yield of 90.7%.

•An α-aminophosphonate extractant was synthesized to extract and separate zirconium and hafnium from sulfate medium.•The extractant can be used for the purification of zirconium.•The stoichiometry of the extracted species was determined.•Thermodynamic functions were calculated for the extraction reaction.A new extractant, bis(2-ethylhexyl)-1-(2-ethylhexylamino)propylphosphonate (BEAP or B) was synthesized to extract and separate zirconium and hafnium from sulfate medium. Under optimum conditions, the separation factor of Zr over Hf was found to be 6.8. The extracted complexes were determined to be ZrO(HSO4)2·3B and HfO(HSO4)2·2B. The extractions of zirconium and hafnium are both exothermic. A counter-current operation was conducted, in which the content of HfO2 was decreased from 3% to 0.6% in the ZrO2 product. It is suggested that much more extraction and scrubbing stages are needed to reach the goal of 0.01% HfO2 in ZrO2 product.

Two 1D calixarene-based coordination polymers, namely [M3(TC4A-SO2)(SSA)(CH3OH)2(H2O)] (M = Co, CIAC-218 and M = Ni, CIAC-219; H4TC4A-SO2 = p-tert-butylsulfonylcalix[4]arene, H2SSA = 5-sulfosalicylic acid), were synthesized under solvothermal conditions and structurally characterized by elemental analysis, IR spectroscopy and single-crystal X-ray diffraction analysis. CIAC-218 acts as a support for the fabrication of Au and Ag nanoparticles. The silver composite shows high performance in the heterogeneous catalytic reduction of 4-nitrophenol, which follows a first order reaction with a rate constant of 0.32 min−1. The Ag/CIAC-218 catalysts were easily recovered for reuse.Two 1D morning glory-like calixarene-based coordination polymers have been obtained by solvothermal reactions, which can act as a support for the fabrication of Au and Ag nanoparticles. The silver composite shows high performance in the heterogeneous catalytic reduction of 4-nitrophenol.Download high-res image (90KB)Download full-size image

To obtain stable and ultrafine Pt nanoclusters, a trigonal prismatic coordination cage with the sulfur atoms on the edges was solvothermally synthesized to confine them. In the structure of {Ni24(TC4A-SO2)6(TDC)12 (H2O)6} (H4TC4A-SO2 = p-tert-butylsulfonylcalix[4]arene; H2TDC = 2,5-thiophenedicarboxylic acid), three Ni4-(TC4A-SO2) SBUs are bridged by three TDC ligands into a triangle and two such triangles are pillared by three pairs of TDC ligands to form a trigonal prism. The cage cavity has 12 sulfur atoms on the surface. Because of the porous structure and strong covalent interaction between metal and sulfur, ultrafine Pt nanoclusters composed of less than ∼18 Pt atoms can be facilely confined in the present trigonal prismatic cage (Pt@CIAC-121). The as-synthesized Pt NCs exhibit higher electrocatalytic activity than commercial Pt/C toward hydrogen evolution reaction.

We report a Johnson hexadecahedronal coordination cage, constructed via 10 Ni4-p-tert-butylthiacalix[4]arene (Ni4-TC4A) units as vertices and 16 5-(pyridin-4-yl)isophthalate (PIP) ligands as tiles. It features a gyroelongated square bipyramidal geometry, equivalent to two square pyramids pillared by a square antiprism, a J17 Johnson solid. Remarkably, the cage compound exhibits a much higher uptake capacity of C3H8 than CH4, representing a promising material for separation of these two gases. In contrast, Co4-TC4A units are linked by PIP ligands and rare {Co4O4Cl2} clusters, providing a one-dimensional bamboo stick-like polymer.

Two kinds of calixarene-based metal–organic coordination cages were obtained at different pH values despite using the same bridging ligand, either 5-(pyridin-3-yl)isophthalic acid (L1) or 5-(5-fluoropyridin-3-yl)isophthalic acid (L2), namely, {[Co4(TC4A)Cl]4(Ln)4(HCOO)4(H2O)4]}·26DMF (CIAC-117 and CIAC-119) and H4{[Co4(TC4A)Cl]4(Ln)8}·18CH3OH·33DMA (CIAC-118 and CIAC-120), where TC4A represents deprotonated p-tert-butylthiacalix[4]arene, and DMF and DMA represent N,N-dimethylformamide and N,N-dimethylacetamide, respectively. Tetrahedral coordination cages (CIAC-117 and CIAC-119) with shuttlecock-like Co4-TC4A secondary building units (SBUs) as the vertices and L1 and L2 as the three-connected linkers were prepared in the presence of tetramethylammonium hydroxide, while truncated octahedral coordination cages (CIAC-118 and CIAC-120) with L1 and L2 as the two-connected linkers were generated upon the addition of HCl. For CIAC-117, two types of activation methods, solvent exchange-heating and direct heating, were used to investigate the removal of guest molecules in the structure. N2 adsorption properties of activated samples were studied. Moreover, selective dye sorption of CIAC-120 was investigated.

A discrete seesaw-like Ni14 cluster is assembled from two sandwich-like Ni4-(TC4A)2 SBUs and two shuttlecock-like Ni3-(TC4A) SBUs (H4TC4A = p-tert-butylthiacalix[4]arene) with two imidazole-4,5-dicarboxylic acid (H3IDC) ligands. The substitution of active coordinated chloride anions with isophthalic acid derivatives leads to four new compounds with similar cluster structures.

Two isostructural 3d-4f compounds with the common formula [Ln2Ni2(SC4AS)2(H2O)6(phen)4]·[Ni(phen)3]2·[Ni(H2O)6]·8H2O (Ln = Er (CIAC-216) and Nd (CIAC-217); H4SC4AS = sulfonylcalix[4]arenetetrasulfonate; phen = 1,10-phenanthroline) were synthesized under hydrothermal conditions and characterized by elemental analyses, IR spectroscopy and thermogravimetric analysis. Single-crystal X-ray diffraction analysis reveals these two compounds exhibit three-dimensional (3D) supramolecular structures in which the heterometallic [Ln2Ni2(SC4AS)2(H2O)6(phen)4]6− units are linked together through π⋯π interactions between phen ligands into a 1D supramolecular chain and further interconnected through hydrogen bonds with [Ni(H2O)6]2+ cations. The calixarene conformation and magnetic properties of both compounds were also discussed.Two isostructural supramolecular 3d-4f (Ni–Er/Nd) compounds of sulfonylcalix[4]arenetetrasulfonate have been obtained by hydrothermal reactions. The coexistence of transition metal and lanthanide ions leads to the distinctly different coordination behavior of calixarene.

Three nanosized flying saucer-like cobalt compounds, [Co28(TC4A)6(3-SH-trz)8(di-S-trz)4(SO4)Cl10(OH)4(CH3OH)4(H2O)6] (CIAC-210), [Co27(TC4A)6(3-SH-trz)8(di-S-trz)4(CO3)0.25(SO3)0.75Cl10(OH)2(CH3OH)2(H2O)4] (CIAC-211) and [Co28(TC4A)6(trz)16(CO3)Cl11(OH)3(CH3OH)2(H2O)6] (CIAC-212), and one ring-like mixed NiNa compound, [Ni18Na6(TC4A)6(3-S-trz)6Cl6(H2O)6] (CIAC-213), were obtained by solvothermal reactions of the metal salts, p-tert-butyltetrathiacalix[4]arene (H4TC4A) and 1H-1,2,4-triazole-3-thiol (1H-3-SH-trz)/1H-1,2,4-triazole-3-carboxylic acid (1H-3-COOH-trz). All these four compounds are feathered with some shuttlecock-like secondary building units (SBUs) which are constructed by four metal atoms capped by a calixarene molecule. In CIAC-210, -211 and -213, the M4-TC4A SBUs are bridged together by 3-SH-trz and its dimer, forming high nuclearity clusters, while in CIAC-212, the SBUs are bridged by 1H-1,2,4-triazole (trz). It is found that not only the kind of metal and the molar ratio of the reactants play important roles in the formation of the clusters, but also the mixed solvents and their ratio affect the final structures. Magnetic measurements suggested that the metal centers exhibit antiferromagnetic interactions for all these four compounds.

An extra-large octahedral coordination cage (CIAC-114) was designed and modeled based on Co4-p-tert-butylsulfonylcalix[4]arene (Co4-(SC4A-SO2)) subunits and 4,4′,4′′-(benzene-1,3,5-triyl-tris(benzene-4,1-diyl))tribenzoate (BBB) ligands via the isomorphic replacement approach built from an analogous cage structure with a smaller size. X-ray crystallography revealed that the crystals obtained through solvothermal synthesis exhibited the anticipated structure. Each CIAC-114 cage is assembled by six tetranuclear Co4-(SC4A-SO2) units as vertices, which bear a four-fold rotational symmetry, and eight tripodal BBB ligands as linkers, which hold a D3h symmetry. Among its analogues CIAC-114 has the largest overall peripheral diameter of 5.4 nm and an internal cavity of 2.7 nm. After treatment by supercritical CO2, a single crystal sample of CIAC-114 transformed into amorphous material with the retention of the cage skeleton, which demonstrated good adsorption properties towards a small drug molecule, ibuprofen (Ibu), evidenced by IR spectroscopy, 1H NMR spectroscopy, N2 sorption analysis, and drug release experiments. The Ibu release experiment in phosphate buffered saline solution (pH = 7.4) revealed that CIAC-114 exhibited a slow drug release behavior.

•These cages have polynuclear metal-thiacalixarene SBUs as the vertices.•All the cages are constructed by linking the ‘lower-rims’ of calixarene molecules.•All the conic cavities of calixarene molecules point outside the cages.•Some apertures communicate the inner cavities and the outside.•The design methodology decides the component condensation mode and cage geometry.Coordination cages have attracted considerable attention because of their intriguing structures and well-defined cavities. Now this research extends into calixarene-based cages, also termed metallo-supramolecular nanocapsules, with examples of resorcin[4]arenes and pyrogallol[4]arenes in the vanguard. This new research area is described here with a particular focus on recent advances in the formation of polyhedral coordination cages (PCCs) based on thiacalix[4]arenes. All of these thiacalix[4]arene-based PCCs have Mx-calix polynuclear secondary building units (PSBUs) as vertices which are bridged by additional metal-oxygen clusters, carboxylic acids, azoles, or other species as the linkers. The molecular structures of calixarenes and the ancillary ligands, and the condensation modes of the PSBUs and the auxiliary entities can affect the cage structure and size. All of these aspects are highlighted in this review, which seeks to guide further investigations into particular aspects of calixarene chemistry.

Two nanoscale coordination cages based on M4-TC4A (M = CoII and FeII; H4TC4A = p-tert-butylthiacalix[4]arene) and 2,2′-bipyridine-4,4′-dicarboxylic acid (H2bpdc) have been synthesized and characterized. In these isostructural structures, there are two kinds of shuttlecock-like M4-TC4A secondary building units, {M4(TC4A)(Cl)} and {M4(TC4A)(SO4)}, which have different coordination environments and are bridged by bpdc molecules into an elongated octahedron through a [6 + 8] condensation. The gas sorption and magnetic properties were studied.

•A calixarene-based tetrahedral coordination cage was obtained.•Four Co4-TC4A shuttlecocks act as the vertices bridged by four SIP molecules.•The structure and coordination mode of SIP play a crucial role in the cage formation.A new cobalt–thiacalix[4]arene compound [(CH3)4N]2 {[Co4Cl(TC4A)(CH3OH)]4(SIP)4(HCOO)2} (CIAC-111) was synthesized by the solvothermal reaction of CoCl2·6H2O, p-tert-butylthiacalix[4]arene (H4TC4A) and 5-sulfoisophthalic acid sodium salt (NaH2SIP). It is featured with a tetrahedral coordination cage with four Co4-TC4A shuttlecock-like subunits as the vertices and four SIP molecules as the tripod linkers located on the triangular faces. The structure and coordination mode of SIP play a crucial role in the formation of such a cage. The magnetic property of this compound was examined.The introduction of tripodal linker 5-sulfoisophthalic acid to the cobalt/thiacalixarene system led to the formation of one unprecedented calixarene-based tetrahedral coordination cages. The structure and coordination mode of the linker play a crucial role in the formation of such a cage.

•A 2D wavelike metal–calixarene aggregate was obtained.•The Co4-TC4A shuttlecock-like SBUs act as the nodes.•In situ generated 5-(4-pyridyl)tetrazolate ligand acts as a linear linker.A novel cobalt–thiacalix[4]arene compound, [Co4Cl2(TC4A)(ptz)2]∙H2O (where H4TC4A = p-tert-butylthiacalix[4]arene; ptz = 5-(4-pyridyl)tetrazolate) was obtained by solvothermal method, in which ptz was in situ-generated by click reaction of 4-cyanopyridine and sodium azide. This compound is featured with some wavelike layer motifs constructed by bridging the shuttlecock-like Co4-TC4A secondary building units (SBUs) with in situ-generated ptz ligands. Magnetic measurement reveals that the cobalt (II) centers exhibit antiferromagnetic interactions.A novel two-dimensional wavelike aggregate was constructed by bridging the shuttlecock-like Co4-TC4A secondary building units (SBUs) with in situ-generated 5-(4-pyridyl)tetrazolate ligands.

In the present work, a novel α-aminophosphonate extractant (Cextrant 230) was synthesized for the extraction and recovery of cerium and thorium from sulphate medium. The introduction of amine group into the phosphate molecule would enhance the extraction of Ce(IV) and Th(IV). The effects of extractant concentration, H2SO4 concentration and temperature on the metal extraction were investigated in detail. It was found that the extraction of Ce(IV), Th(IV) and REs (La, Gd, Yb) in sulphate medium decreased in the following order: Ce(IV)>Th(IV)>REs(III). A solvent extraction process to extract and recover cerium and thorium from bastnasite leaching was proposed, in which the purities of cerium and thorium products reached 99.9% and 99% with yield of 92% and 98%, respectively.Extraction of Ce4+, Th4+ and other RE3+ with Cextrant 230 in sulphuric acid medium ([Ce4+]=[Th4+]=[Yb3+]= [Gd3+]=[La3+]=0.01 mol/L, CL=0.1 mol/L)Download high-res image (56KB)Download full-size image

An extra-large octahedral coordination cage (CIAC-114) was designed and modeled based on Co4-p-tert-butylsulfonylcalix[4]arene (Co4-(SC4A-SO2)) subunits and 4,4′,4′′-(benzene-1,3,5-triyl-tris(benzene-4,1-diyl))tribenzoate (BBB) ligands via the isomorphic replacement approach built from an analogous cage structure with a smaller size. X-ray crystallography revealed that the crystals obtained through solvothermal synthesis exhibited the anticipated structure. Each CIAC-114 cage is assembled by six tetranuclear Co4-(SC4A-SO2) units as vertices, which bear a four-fold rotational symmetry, and eight tripodal BBB ligands as linkers, which hold a D3h symmetry. Among its analogues CIAC-114 has the largest overall peripheral diameter of 5.4 nm and an internal cavity of 2.7 nm. After treatment by supercritical CO2, a single crystal sample of CIAC-114 transformed into amorphous material with the retention of the cage skeleton, which demonstrated good adsorption properties towards a small drug molecule, ibuprofen (Ibu), evidenced by IR spectroscopy, 1H NMR spectroscopy, N2 sorption analysis, and drug release experiments. The Ibu release experiment in phosphate buffered saline solution (pH = 7.4) revealed that CIAC-114 exhibited a slow drug release behavior.