Xinxin Hang

Ultrafine Pt Nanoclusters Confined in a Calixarene-Based {Ni24} Coordination Cage for High-Efficient Hydrogen Evolution Reaction

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.

Discrete {Ni40} Coordination Cage: A Calixarene-Based Johnson-Type (J17) Hexadecahedron

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.

pH-dependent formation of different coordination cages based on Co4-TC4A secondary building units and bridging ligands

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.

Calixarene-Based {Ni18} Coordination Wheel: Highly Efficient Electrocatalyst for the Glucose Oxidation and Template for the Homogenous Cluster Fabrication

Catalyst plays a very important role in the exploration of new energy. To obtain a highly efficient electrocatalyst for the glucose oxidation and tiny metal nanocluster catalysts, a calixarene-based {Ni18} coordination wheel with sulfur atoms on the cavity surface was designed, synthesized, and used as the porous template. Contributing from the active sites of nickel cations, the as-synthesized coordination wheels can efficiently catalyze the electrochemical oxidation of glucose with the onset and peak potentials of 0.3 and 0.46 V in alkaline medium, and the catalysis does not depend on the atmosphere (N2, air, or O2), which indicates that the coordination wheel will be a promising electrocatalyst candidate for the compartmentless glucose-air fuel cell. Meanwhile, benefiting from its confined cavity and inner sulfur surface, such a coordination wheel can serve as a general template for the fabrication and encapsulation of tiny metal nanoclusters of Au, Pd, Ir, Ru, Rh, Pt, and AuPd. In electrochemical examinations, the bimetallic AuPd clusters confined in the coordination wheel show higher current density than commercial Pt/C toward hydrogen evolution reaction (HER). The present study shows that the designed coordination wheel can be used as not only a type of novel catalyst itself but also a class of templates for metal cluster catalysts.