Mapping the formation areas of giant molybdenum blue clusters: a spectroscopic study.

The self-assembly of soluble molybdenum blue species from simple molybdate solutions has primarily been associated with giant mixed-valent wheel-shaped cluster anions, derived from the {Mo(V/VI)(154/176)} archetypes, and a {Mo(V/VI)(368)} lemon-shaped cluster. The combined use of Raman spectroscopy and kinetic precipitation as self-assembly monitoring techniques and single-crystal X-ray diffraction is key to mapping the realm of molybdenum blue species by establishing spherical {Mo(V/VI)(102)}-type Keplerates as an important giant molybdenum blue-type species. We additionally rationalize the empirical effect of reducing agent concentration on the formation of all three relevant skeletal types: wheel, lemon and spheres. Whereas both wheels and the lemon-shaped {Mo(V/VI)(368)} cluster are obtained from weakly reduced molybdenum blue solutions, considerably higher reduced solutions lead to {Mo(V/VI)(102)}-type Keplerates.

Polyoxometalate-directed assembly of water-soluble AgCl nanocubes.

"Out-of-pocket" association of Ag(+) to the tetradentate defect site of mono-vacant Keggin and Wells-Dawson polyoxometalate (POM) cluster-anions is used to direct the formation of water-soluble AgCl nanocubes.

Acetate-controlled demetalation in multiiron polyoxometalates: a triiron cluster trapped between beta- and gamma-Keggin isomers.

Acetate-induced demetalation of a {gamma-SiW(10)Fe(2)}-based dimer affords an acetato/hydroxo-bridged triiron cluster stabilized by two isomerically distinct Keggin units.

Acetate-driven polyoxometalate demetalation: an open-shell diiron polytungstate comprising two rotational Keggin isomers.

The effect of acetate concentration on the formation of {SiW10Fe2}-based complexes is demonstrated by the synthesis of an open-shell diiron tungstosilicate derivative featuring two rotational Keggin isomer units.

Tetrairon and hexairon hydroxo/acetato clusters stabilized by multiple polyoxometalate scaffolds. Structures, magnetic properties, and chemistry of a dimer and a trimer.

Investigation of the catalytically relevant gamma-diiron(III) Keggin complexes in aqueous acetate buffer leads to a dimeric C(2v)-symmetric polyanion, [{Fe(OH)(OAc)}(4)(gamma-SiW(10)O(36))(2)](12-) (3) and a trimeric C(2)-symmetric polyanion, [{Fe(6)(OH)(9)(H(2)O)(2)(OAc)(2)}(gamma-SiW(10)O(36))(3)](17-) (4). Polyanion 3 incorporates a hydroxo/acetato-bridged tetrairon(III) core, while 4 incorporates a trigonal prismatic hydroxo/acetato-bridged hexairon(III) core. The monomeric building unit of 3 and 4, {gamma-SiW(10)Fe(2)}, adopts the "out-of-pocket" structural motif (with two corner-sharing FeO(6) coordination polyhedra no longer connected to the internal SiO(4) tetrahedron of the Keggin unit) also observed in the {gamma-SiW(10)Fe(2)}(-)type structures isolated from nonbuffered aqueous solutions. Following hydrolysis, 3 is converted to 4 as confirmed by (29)Si NMR. Magnetic measurements establish that in both 3 and 4 all exchange interactions are antiferromagnetic.

The true nature of the Di-iron(III) gamma-Keggin structure in water: catalytic aerobic oxidation and chemistry of an unsymmetrical trimer.

The complex [gamma(1,2)-SiW(10){Fe(OH(2))}(2)O(38)](6)(-) (1) has been reported to catalyze the much sought reductant-free selective O(2)-based epoxidation of alkenes (Nishiyama, Y.; Nakagawa, Y.; Mizuno, N. Angew. Chem. Int. Ed. 2001, 40, 3639-3641) in chlorocarbon-acetonitrile solution. The challenge of reproducing catalysis by 1 led us to examine this chemistry in detail. In H(2)O, a desirable solvent for catalysis, 1, does not exist in the proposed organic-medium form in which the two iron atoms are in the binding pocket defined by the equatorial oxygens and, importantly, by two oxygens bound to the central Si heteroatom. Instead, 1 in H(2)O initially forms an unusual trimer [{Fe(2)(OH)(3)(H(2)O)(2)}(3)(gamma-SiW(10)O(36))(3)](15)(-) (2). The X-ray structure of 2 shows that the Fe-O(Si) bonds are cleaved and new bonds (mu-hydroxo bridges) form between these Fe centers and those of the neighboring [gamma(1,2)-SiW(10)Fe(2)] units. Structural, physical, and computational evidence indicate that if the bonds between the d-electron center, M (Fe in the case of 1 and 2), and the terminal ligands on M are stronger than the M-O(x)() bonds, then the out-of-pocket form is more stable and is the one observed. Significantly, 2 in H(2)O forms an intermediate that catalyzes the effective aerobic oxidation of sulfur compounds (mercaptoethanol is oxidized to the corresponding disulfide by O(2) at ambient pressure and temperature). All experimental findings are consistent with dissociation of a gamma-SiW(10) Keggin unit from the trimer, 2, to form the catalytically active species.

A nanoring-nanosphere molecule, {Mo214V30}: pushing the boundaries of controllable inorganic structural organization at the molecular level.

A controlled, Raman-monitored chemical reduction of a molybdate and vanadate mixture affords a new type of molybdenum-oxide-based cluster showing an unprecedented level of inorganic structural organization. The cluster incorporates two nanosized substructures (a ring and a sphere) in an open clam-like assembly. Multiple methods indicate that the nanoring contains delocalized electrons and the nanosphere contains localized but interacting electrons.

The role of the central atom in structure and reactivity of polyoxometalates with adjacent d-electron metal sites. computational and experimental studies of gamma-[(Xn+O4)RuIII2(OH)2(MFM)10O32](8-n)-) for MFM = Mo and W, and X = AlIII, SiIV, PV, and SVI.

The role of the central atom X in the structure and reactivity of di-Ru-substituted gamma-Keggin polyoxometalates (POMs), gamma-[(Xn+O4)RuIII2(OH)2(MFM)10O32](8-n)-), where MFM = Mo and W, and X = AlIII, SiIV, PV, and SVI., was computationally investigated. It was shown that for both MFM = Mo and W the nature of X is crucial in determining the lower lying electronic states of the polyoxoanions, which in turn likely significantly impacts their reactivity. For the electropositive X = AlIII, the ground state is a low-spin state, while for the more electronegative X = SVI the ground state is a high-spin state. In other words, the heteroatom X can be an "internal switch" for defining the ground electronic states of the gamma-M2-Keggin POMs. The obtained trends, in general, are less pronounced for MFM = Mo than for W. On the basis of the comparison of the calculated energy gaps between low-spin and high-spin states of polytungstates and polymolybdates, we predict that the gamma-M2-Keggin polytungstates could be more reactive than their polymolybdate analogues. For purposes of experimental verification the computationally predicted and evaluated polytungstate gamma-[(SiO4)RuIII2(OH)2(OH2)2W10O32]4- was prepared and characterized.

Ferrimagnetically ordered nanosized polyoxomolybdate-based cluster spheres.

The self-assembly of molybdate building units in the presence of Fe(II) and V(IV) produces the first mixed-spin heterometal keplerate-type clusters displaying ferrimagnetic interactions.

[{(Mo)Mo5O21(H2O)3(SO4)}12(VO)30(H2O)20]36-: a molecular quantum spin icosidodecahedron.

Self-assembly of aqueous solutions of molybdate and vanadate under reducing, mildly acidic conditions results in a polyoxomolybdate-based {Mo72V30} cluster compound Na8K16(VO)(H2O)5[K10 subset{(Mo)Mo5O21(H2O)3(SO4)}12(VO)30(H2O)20].150H2O, 1, a quantum spin-based Keplerate structure.

Asymmetric terminal ligation on substituted sites in a disorder-free Keggin anion, [beta-SiFe2W10O36(OH)2(H2O)Cl]5-.

A new monomeric diiron beta-Keggin derivative, [(CH3)2NH2]5[beta-SiFe2W10O36(OH)2(H2O)Cl].7H2O (1) with non-adjacent substituted sites has been obtained in good yield by reaction of Fe(III) cations with [gamma-SiW10O36]8- in aqueous solution. The use of hydrogen bonding counter-cations produced a disorder-free polyanion. This situation facilitates unequivocal identification of the terminal ligands on Fe atoms and interpretation of the magnetic properties, which are also addressed by DFT calculations. Electrochemical studies establish that 1 can be step-wise reduced by two electrons and then reversibly oxidized.

A potassium selective 'nanosponge' with well defined pores.

The novel spherical cluster-compound K2Na6[K20 [symbol: see text] Mo80-V22O282(SO4)12(H2O)66]. approximately 140H2O 1 has been obtained in a 'one-pot' reaction and exhibits several remarkable structural features: 30 open shell centers, i.e. 8 Mov and 22 VIV spanning an icosidodecahedron, the incorporation of 20 K+ cations capping 20 appropriate [M6O6] pores/rings present at the surface of the spherical cluster-anion, and an encapsulated aggregate of water molecules.