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The synthesis of a novel dititanium-substituted gamma-Keggin polyoxometalates (POM), [{gamma-SiTi2W10O36(OH)(sub 2)}(sub 2)(mu-O)(sub 2)](super 8-) (1), containing an edge-shared dinuclear Ti site, and its molecular structure are described. The results have shown that the dinuclear titanium core of 1 catalyzes mono-oxygenation reactions, such as epoxidation of olefins and sulfoxidation of sulfides with hydrogen peroxide.

Structural characterization studies were performed on the dioxoruthenium(VI) porphyrin cation radical derivatives synthesized from the stoichiometric oxidation of Ru(VI)-TMP(O)2 and Ru(VI)OEP(O)2 using phenoxathiin hexachloroantimonate. Spectroscopic analyses utilizing nuclear magnetic resonance, ultraviolet/visible and electron spin resonance measurements determined the electronic structure of the oxidation products. Additional oxidation reaction studies provided further data regarding the reactivity of each complex.

NMR, ESR, solution magnetic susceptibility and UV-vis spectral measurements were utilized in the characterization of (FePor)1-. This anion resulted from the two-electron reduction of Fe(super III)OEP and Fe(super III)TPP derivatives. Results revealed that the electron-withdrawing substituents on the prophyrin ring effect the formation of four types of porphyrin complexes which include four-coordinated iron(I) low-spin porphyrin, five-coordinated iron(I) low-spin porphyrin, four-coordinated iron(II) low-spin porphyrin anion radical and five-coordinated iron(II) high-spin porphyrin anion radical.

The synthesis and structural characterization of a new complex, a [gamma]-keggin dimeric silicotungstate with [Zr.sup.2][([mu]-OH).sub.2] core is reported.

The promotion of the heterolytic O-O bond cleavage of (hydroperoxo)iron(III) porphyrin complex is studied by analysis of the rate constants of the meso positions of the porphyrin ring. It is observed that the effectivity lies on the electron-donating groups of the substituted porphyrin rings. It is concluded that the internal electron donor to destabilize the O-O bond is relevant for the formation of corresponding oxoiron(IV) porphyrin cation radicals.

A novel dinuclear zirconium sandwich-type silicotungstate cluster of [(γ-SiW10O36)2Zr2(μ-OH)2]10- (1) was synthesized by the reaction of a divacant lacunary γ-Keggin silicotungstate [γ-SiW10O36]8- with ZrOCI2·8H2O. The anion consisted of two [γ-SiW10O36]8- units sandwiching a diamond Zr2(μ-OH)2 core, and each zirconium atom in 1 was six-coordinated to two μ-OH ligands and four oxygen atoms of two [γ-SiW10O36]8- units. The Zr2(μ-OH)2 core in 1 reacted with methanol to give the corresponding monomethoxo derivative [(γ-SiW10O36)2Zr2(μ-OH)(μ-OCH3)]10- (2). [ABSTRACT FROM AUTHOR]

A ring-shaped polyoxometalate (POM), [P 8 W 48 O 184 ] 40- (P8W48), formed by condensation of four hexavacant lacunary α-Dawson-type [α-P 2 W 12 O 48 ] 14- units, is an attractive superlacunary compound possessing a large cavity (approximately 10 Å). Although the introduction of metal species into the cavity was attempted in aqueous media using the K + /Li + salt of P8W48, we encountered several challenges: excess metal species are required, and K + and/or Li + remain in the cavity. Therefore, controlling the number and arrangement of the introduced metal species proved difficult. In this study, we overcame the aforementioned problems by developing a novel method for introducing metal species in organic media by employing the organic-solvent-soluble tetra- n-butylammonium (TBA) salt of P8W48 (I, TBA 12 H 28 [P 8 W 48 O 184 ]·30H 2 O). We began by synthesizing compound I via a cation exchange reaction of the K + /Li + salt of P8W48 with TBABr in aqueous nitric acid. Single crystals (I', TBA 14 H 26 [P 8 W 48 O 184 ]·20H 2 O·2CH 3 NO 2 ) were obtained by recrystallizing I from a nitromethane/toluene mixture in the presence of excess TBAOH. The bond valence sum values of I' showed that protons were located on the oxygen atoms inside the ring, and thus highly reactive sites capable of reacting with metal species were selectively generated within the ring. When I was reacted with 8 equiv of 3d metal species (Mn 2+ , Co 2+ , Ni 2+ , Cu 2+ , or Zn 2+ ) in an acetonitrile/1,2-dichloroethane mixture in the presence of TBAOH and methanol, a series of POMs with eight metal sites (II M , TBA 14 H 2 [{M 2 (OH 2 ) 2 } 2 {M(OH 2 ) 2 } 4 P 8 W 48 O 176 (OCH 3 ) 8 ]· nH 2 O· mCH 3 CN, where M = Mn, Co, Ni, Cu, Zn) was synthesized. In II M , two edge-sharing bis(square-pyramidal) {(μ-O) 2 (M-OH 2 )(μ 3 -O) 2 (M-OH 2 )(μ-O) 2 } and four isolated M(OH 2 ) 2 sites were present within the cavity. During the metal introduction, two α-P2W12 units were converted into γ-P2W12 units, and unique α,γ,α,γ-type P8W48 frameworks were obtained.

In this paper, the synthesis and magnetic properties of mononuclear Fe III -containing polyoxometalates (POMs) with different types of heteroatoms, TBA 7 H 10 [(A-α-XW 9 O 34 ) 2 Fe] (II X , X = Ge, Si; TBA = tetra- n-butylammonium), are reported. In these POMs, mononuclear highly distorted six-coordinate octahedral [FeO 6 ] 9- units are sandwiched by two trivacant lacunary units [A-α-XW 9 O 34 ] 10- (X = Ge, Si). These POMs exhibit field-induced slow magnetic relaxation based on the single high-spin Fe III magnetic center ( S = 5/2). Combining experiment and ab initio calculations, we investigated the effect of heteroatoms of the lacunary units on the field-induced slow magnetic relaxation of these POMs. By changing the heteroatoms from Si (II Si ) to Ge (II Ge ), the coordination geometry around the Fe III ion is mildly changed. Concretely, the axial Fe-O bond length in II Ge is shortened compared with that in II Si , and consequently the distortion of the [FeO 6 ] 9- unit in II Ge from the ideal octahedral coordination geometry becomes larger than that in II Si . The effective demagnetization barrier of II Ge (11.4 K) is slightly larger than that of II Si (9.2 K). Multireference ab initio calculations predict zero-field splitting parameters in good agreement with experiment. Although the differences in the coordination geometries and magnetic properties of II Ge and II Si are quite small, ab initio calculations indicate subtle changes in the magnetic anisotropy which are in line with the observed magnetic relaxation properties.