Synthesis and structure of a sodium complex of an aromatic beta-diketone and pyrazolylpyridine

Reaction of NaH with a THF solution of Eu(BTA)3(pypzH) [BTA = 1-benzoyl-3,3,3-trifluoroacetonate, pypzH = 2-(3-pyrazolyl)pyridine] leads to the formation of the europium-free tetrasodium complex [Na(4)(pypzH)(2)(micro4-BTA)(2)(micro2-BTA)(2)]. Single-crystal X-ray diffraction studies revealed the presence of a centrosymmetric Na+ hybrid tetramer,which fully occupies the contents of the triclinic unit cell. The crystal structure contains two individual Na+ cations, Na(1) and Na(2), which have highly irregular [NaN(2)O(3)] and[NaO(6)] local coordination environments, respectively. One of the key features is the presence of a central [Na(4)O(6)] core, which is unprecedented for Na+ . Externally to this [Na(4)O(6)] cluster pyrazolylpyridine organic molecules are N,N-chelated to Na(1). Even though all of the organic residues contain aromatic rings, the crystal packing of individual centrosymmetric tetrasodium [Na(4)(pypzH)(2)(micro4-BTA)(2)(micro2-BTA)(2)] molecular moieties is essentially driven through geometrical aspects combined with weak C-H...pi interactions, rather than the expected a priori pi-pi interactions. The material also contains classical strong hydrogen bonds, even though these do not directly contribute to the packing driving forces.     

Molybdenum oxide/bipyridine hybrid material {[MoO3(bipy)][MoO3(H2O)]}n as catalyst for the oxidation of secondary amines to nitrones

The inorganic-organic hybrid material {[MoO₃(bipy)][MoO₃(H₂O)]}_n (bipy = 2,2′-bipyridine) can be used as a water-tolerant catalyst for the oxidation of secondary amines under mild conditions using either urea hydrogen peroxide (UHP) or tert-butylhydroperoxide (TBHP) as the oxidant. Under optimized reaction conditions (2 mol % catalyst, 3-4 equiv TBHP, CH₂Cl₂ as the solvent, 40 °C), the corresponding nitrones were obtained with different efficiency depending on the nature of the cyclic or acyclic amine used.     

A study of rearrangement processes in the mass spectra of substituted benzophenones which provide a guide to orientation

An investigation of the mass spectra of substituted benzophenones has shown that a number of rearrangement processes are operative. The rearrangements have been shown to involve solely the ortho-substituents to the carbonyl group and in many cases the carbonyl oxygen atom itself participates in the processes. Deuterium labelling experiments combined with data obtained from accurate mass and metastable analysis have enabled the probable mechanisms of rearrangement and fragmentation to be elucidated. An understanding of these processes should greatly assist in the location of substituents in unknown benzophenones.     

57Fe Mössbauer Spectroscopy Studies of Meteorites: Implications for Weathering Rates,Meteorite Flux,and Early Solar System Processes

Ordinary chondrite finds, terrestrial age dated using ¹⁴C analyses, from different meteorite accumulation sites, have been examined by Mössbauer spectroscopy to quantitatively determine terrestrial oxidation. We observe differences in weathering rates between sites, and also between different chondrite groups. A comparison of weathering over time, and its effect in eroding meteorites, together with the number and mass distribution of meteorites in each region, enables us to derive estimates of the number of meteorite falls over a given mass per year. Studies of how the oxygen isotopic composition of samples varies with weathering indicate that incipient alteration may occur without a pronounced isotopic effect, possibly due to weathering of silicates to topotactically oriented smectite confined spaces where the water volume is limited. This finding has profound implications for the use of oxygen isotopes as a tool in understanding water–rock interaction. It also may reconcile previously contradictory data regarding the nebular or asteroidal location of pre-terrestrial aqueous alteration. Finally, Mössbauer spectroscopy is also found to be a useful tool in determining mineral abundance in carbonaceous chondrites, where a fine-grained matrix makes traditional approaches inapplicable. Again, the results have implications for the modification of chondritic materials in the early solar system.     

Study of the Inclusion Compound Formed between a Luminescent Europium(III) β-Diketonate Complex and γ-Cyclodextrin

A 1 : 1 inclusion compound between -CD and the tris chelate complex Eu(NTA)₃·2H₂O [NTA = 1-(2-naphthoyl)-3,3,3-trifluoroacetone)] was prepared and characterized in the solid-state by powder X-ray diffraction, thermogravimetric analysis, FTIR, ¹³C CP MAS NMR and photoluminescence spectroscopy. Possible host-guest interaction geometries were generated from ab initio calculations. The photoluminescence results reveal the presence of a metal-to-ligand energy transfer that is much more efficient than that previously reported for the analogous -CD adduct.     

Multiply Bonded Dimolybdenum Cation Immobilized in Mesoporous Silica: XAFS Analysis and Catalytic Activity in Cyclopentadiene Polymerization

MCM‐41 derivatized with the cis‐[Mo₂(μ‐O₂CMe)₂(MeCN)₆]²⁺ cation has been characterized by means of XAFS spectroscopy and shown to be active as an initiator for the cationic polymerization of methylcyclopentadiene. The Mo‐Mo quadruple bond is not disrupted during the fixation on the surface.     

Molybdenum(VI) catalysts obtained from η3-allyl dicarbonyl precursors: synthesis, characterization and catalytic performance in cyclooctene epoxidation

The oxidative decarbonylation of the η(3)-allyl dicarbonyl complexes [Mo(η(3)-C(3)H(5))Cl(CO)(2)(L)] (L = 2,2'-bipyridine (bipy) (1), 4,4'-di-tert-butyl-2,2'-bipyridine (di-tBu-bipy) (2)) by reaction with aqueous tert-butylhydroperoxide (TBHP) or H(2)O(2) gave the following compounds in good to excellent yields: the oxo-bridged dimers [MoO(2)Cl(L)](2)O (L = bipy (3), di-tBu-bipy (6)) using TBHP(10 equiv.)/CH(3)CN/r.t.; the molybdenum oxide/bipyridine hybrid material {[MoO(3)(bipy)][MoO(3)(H(2)O)]}(n) (4) and the octanuclear complex [Mo(8)O(24)(di-tBu-bipy)(4)] (7) using TBHP(50 equiv.)/H(2)O/70 °C; the oxodiperoxo complexes MoO(O(2))(2)(L) (L = bipy (5), di-tBu-bipy (8)) using H(2)O(2)(10 equiv.)/CH(3)CN/r.t. The structure of 7·x(solvent) (where solvent = CH(2)Cl(2) and/or diethyl ether) was determined by single crystal X-ray diffraction. Despite possessing the same windmill-type complex as that described previously for 7·10CH(2)Cl(2), the crystal structure of 7·x(solvent) is unique due to differences in the crystal packing. Compounds 1-8 were examined as catalysts or catalyst precursors for the epoxidation of cyclooctene using aqueous TBHP or H(2)O(2) as oxidant at 55 or 70 °C. Reactions were performed without co-solvent or with the addition of water, ethanol or acetonitrile. Cyclooctene oxide was always the only reaction product. Solids recovered after 24 h reaction at 70 °C were identified by FT-IR spectroscopy as the hybrid 4 from (1,3-5)/TBHP, complex 5 from (1,3-5)/H(2)O(2), and complex 8 from (2,6-8)/H(2)O(2). With TBHP as oxidant, the highest epoxide yields (for 24 h reaction at 70 °C) were obtained using excess H(2)O as solvent (28-38% for 1,3-5; 87-98% for 2,6-8), while with H(2)O(2) as oxidant, the highest epoxide yields were obtained using CH(3)CN as solvent (54-81% for 3-8).     

Crystal and supramolecular structures of dioxomolybdenum(VI) and dioxotungsten(VI) complexes of dihydroxybenzoic acids

The tetramethylammonium salts (NMe₄)₂[MO₂(2,3-Hdhb)₂]·2H₂O and (NMe₄)₂[MO₂(3,4-Hdhb)₂]·6H₂O (M = Mo, W; Hdhb = monoprotonated form of 2,3- or 3,4-dihydroxybenzoic acid, 2,3-H₃dhb or 3,4-H₃dhb) were prepared and their crystal structures determined. The structure of [Mg(H₂O)₆](NMe₄)₄[MoO₂(3,4-dhb)(3,4-Hdhb)]₂·13H₂O, obtained by the recrystallization of (NMe₄)₂[MoO₂(3,4-Hdhb)₂] in the presence of magnesium ions, is also reported. The supramolecular interactions of the five structures are discussed in detail concerning the hydrogen bonding patterns involving complexes and water molecules of crystallization.     

Synthesis and catalytic properties of molybdenum(VI) complexes with tris(3,5-dimethyl-1-pyrazolyl)methane

The complex [MoO(2)Cl{HC(3,5-Me(2)pz)(3)}]BF(4) (1) (HC(3,5-Me(2)pz)(3) = tris(3,5-dimethyl-1-pyrazolyl)methane) has been prepared and examined as a catalyst for epoxidation of olefins at 55 °C using tert-butyl hydroperoxide (TBHP) as the oxidant. For reaction of cis-cyclooctene, epoxycyclooctane is obtained quantitatively within 5 h when water is rigorously excluded from the reaction mixture. Increasing amounts of water in the reaction mixture lead to lower activities (without affecting product selectivity) and transformation of 1 into the trioxidomolybdenum(VI) complex [{HC(3,5-Me(2)pz)(3)}MoO(3)] (4). Complex 4 was isolated as a microcrystalline solid by refluxing a suspension of 1 in water. The powder X-ray diffraction pattern of 4 can be indexed in the orthorhombic Pnma system, with a = 16.7349(5) ?, b = 13.6380(4) ?, and c = 7.8513(3) ?. Treatment of 1 in dichloromethane with excess TBHP led to isolation of the symmetrical [Mo(2)O(4)(μ(2)-O){HC(3,5-Me(2)pz)(3)}(2)](BF(4))(2) (2) and unsymmetrical [Mo(2)O(3)(O(2))(2)(μ(2)-O)(H(2)O){HC(3,5-Me(2)pz)(3)}] (3) oxido-bridged dimers, which were characterized by single-crystal X-ray diffraction. Complex 2 displays the well-known (Mo(2)O(5))(2+) bridging structure where each dioxidomolybdenum(VI) center is coordinated to three N atoms of the organic ligand and one μ(2)-bridging O atom. The unusual complex 3 comprises dioxido and oxidodiperoxo molybdenum(VI) centers linked by a μ(2)-bridging O atom, with the former center being coordinated to the tridentate N-ligand. The dinuclear complexes exhibit a similar catalytic performance to that found for mononuclear 1. For complexes 1 and 2 use of the ionic liquids (ILs) 1-butyl-3-methylimidazolium tetrafluoroborate and N-butyl-3-methylpyridinium tetrafluoroborate as solvents allowed the complexes to be completely dissolved, and in each case the catalyst and IL could be recycled and reused without loss of activity.