Cuboctahedral Cages Research Articles

Metal−Organic Polyhedral Frameworks: High H2 Adsorption Capacities and Neutron Powder Diffraction Studies

Neutron powder diffraction experiments on D(2)-loaded NOTT-112 reveal that the axial sites of exposed Cu(II) ions in the smallest cuboctahedral cages are the first, strongest binding sites for D(2) leading to an overall discrimination between the two types of exposed Cu(II) sites at the paddlewheel nodes. Thus, the Cu(II) centers within the cuboctahedral cage are the first sites of D(2) binding with a Cu-D(2) distance of 2.23(1) A.

Highly Stable Crystalline Catalysts Based on a Microporous Metal−Organic Framework and Polyoxometalates

A series of remarkable crystalline compounds [Cu(2)(BTC)(4/3)(H(2)O)(2)](6)[H(n)XM(12)O(40)].(C(4)H(12)N)(2) (X = Si, Ge, P, As; M = W, Mo) were obtained from the simple one-step hydrothermal reaction of copper nitrate, benzentricaboxylate (BTC), and different Keggin polyoxometalates (POMs). In these compounds, the catalytically active Keggin polyanions were alternately arrayed as noncoordinating guests in the cuboctahedral cages of a Cu-BTC-based metal-organic framework (MOF) host matrix. X-ray crystallographic analyses, TG, FT-IR, UV-vis, N(2) adsorption studies, and acid-base titration demonstrated their high stability and toleration for thermal and acid-base conditions. No POM leaching or framework decomposition was observed in our study. The representative acid catalytic performance of a compound containing PW(12) species was assessed through the hydrolysis of esters in excess water, which showed high catalytic activity and can be used repeatedly without activity loss. Moreover, catalytic selectivity, which is dependent on the molecular size of substrates, and substrate accessibility for the pore surface were observed. It is the first time that the well-defined, crystalline, MOF-supported POM compound has behaved as a true heterogeneous acid catalyst. The unique attributes of MOF and well-dispersed level of POMs prohibited the conglomeration and deactivation of POMs, which allowed for the enhancement of their catalytic properties.

Reductive Activation oftripodMetal Compounds: Preparative Application

AbstractThetripodnickel(0) species [tripod4Ni3] (1) {tripod= CH3C(CH2PPPh2)3} is shown to undergo oxidative addition with disulfides or diselenides REER (E = S, Se, R =tBu, Ph) to produce [tripodNi(ER)] (2). Compounds2show pseudo tetrahedral coordination. They are paramagnetic with one unpaired electron per molecule. Their magnetic behaviour is almost that of an ideal Curie‐type magnet down to temperatures of 2 K. They undergo reversible one electron oxidation to the 16 valence electron species [tripodNi(ER)]+. The isoelectronic pseudo tetrahedral 16 valence electron cobalt species [tripodCo(ER)] (3) are obtained by reduction of CoCl2with KC8in the presence oftripodand subsequent reaction with REER (E = S, Se; R =tBu, Ph). They are paramagnetic with two unpaired electrons per molecule. They can be reversibly oxidised to the 15 valence electron compounds [tripodCo(ER)]+while their reduction to the 17 valence electron species [tripodCo(ER)]–, which would be isoelectronic to the stable compounds2, is not observed. Under appropriate conditions the reactions with REER do not result in the formation of3but yield [tripodCoECotripod] (4) by extrusion of sulfur and selenium from the substrate. Compounds4show a linear Co–E–Co framework with very short Co–E bonds (E = S: 205 pm; E = Se: 216 pm). They are members of a family of dimetallaheterocumulenic compounds [LnMEMLn] (E = main group element of groups III to VI) with a valence electron count of 36 electrons. Quantum chemistry predicts that the HOMO of such compounds should be a degenerated pair of mainly metal centred orbitals. Electrochemistry of4a, [tripodCoSCotripod], shows three quasi‐reversible oxidation steps in the range of –700 mV vs. SCE to 570 mV vs. SCE, which can be understood as metal centred oxidations. Three different types of crystals have been obtained for different types of pseudopolymorphs4a. The geometric parameters of the coordination compounds are almost equal in these pseudopolymorphic crystals. The real difference is the content of solvent molecules and, hence, the packing of the molecules. In the crystals of4acontaining no solvent the coordination compounds form close packed layers stacked on each other in an oblique way. In the crystals containing4a·DME a layer of solvent molecules separates each pair of layers of close packed molecules. In the crystal of4a·3DME a cuboctahedral cage of solvent molecules embedding each coordination compound separates the complex molecules from each other. The different types of crystals observed underpin the globular shape of4and the effective shielding power of thetripodligand. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Synthesis and X-ray structure of the [{Fe3(CO)9(µ3-O)}2H]3−trianion: dimerization of a metal carbonyl cluster via formation of an exceptionally short hydrogen bond

The synthesis, structure and characterization of the [{Fe3(CO)9(micro3-O)}2H]3- trianion in its [Cs(THF)0.33]+ and [NEt4]+ salt are reported. The title dimeric cluster has been obtained by protonation in water or in organic solvent of the [Fe3(CO)9(micro3-O)]2- dianion to the hydroxo [Fe3(CO)9(micro3-OH)]- derivative and crystallization. The solid state structure of [Cs(THF)0.33]3[{Fe3(CO)9(micro3-O)}2H] is based on ionic packing of [Cs(THF)0.33]+ cations and [{Fe3(CO)9(micro3-O)}2H]3- trianions. The fractional formula is due to the particular packing of Cs+ cations, which are at the vertices of fused cuboctahedral and trigonal antiprismatic polyhedrons. Each cuboctahedron encapsulates a [{Fe3(CO)9(micro3-O)}2H]3- trianion, whereas each trigonal antiprism encapsulates a THF molecule. The possibility that the structure of the [{Fe3(CO)9(micro3-O)}2H]3- trianion could be affected by its confinement in the cuboctahedral cage of Cs+ ions and the heavy disorder of the THF molecule urged a further structural determination of the trianion with a completely different cation. The corresponding [NEt4]3[{Fe3(CO)9(micro3-O)}2H] salt has been, therefore, prepared and structurally characterized. The [{Fe3(CO)9(micro3-O)}2H]3- trianion displays an identical structure and almost coincident molecular parameters in both salts. Its most notable feature is represented by the unique hydrogen atom symmetrically bridging the micro3-O atoms of two different [Fe3(CO)9(micro3-O)]2- molecules and displaying one of shortest O...H...O interaction so far reported in organic, inorganic and organometallic literature. The structure of [Cs(THF)]2[Fe4(CO)13], which has been obtained as a by-product of the synthesis of [Cs(THF)0.33]3[{Fe3(CO)9(micro3-O)}2H], is also briefly reported.