Daniele Cauzzi

Temperature‐Dependent Fluorescence of Cu5 Metal Clusters: A Molecular Thermometer

The accurate measurement of temperature is of increasing importance as it is required for widespread applications (electronic devices, biology, medical diagnostics). In this context, fluorescence thermometry has already shown great potential, and a variety of molecules have been proposed as luminescent molecular thermometers. Herein, we describe Cu5 metal cluster 1 (Figure 1) that presents remarkable photophysical properties, both in solution and as the solid, characterized by temperature-dependent emission intensity and lifetime that change significantly in the range between 45 and + 80 8C. These properties allow for an unprecedented accuracy in temperature determination by fluorescence measurements, with the high sensitivity and the high temporal (sub-millisecond) and spatial (sub-micrometer) resolution typical of photoluminescence spectroscopy. Complex 1 can be seen as a metal nanoparticle composed of five copper atoms bound to three highly conjugated dianionic cationic ligands (EtNC(S)PPh2NPPh2C(S)NEt) ; Figure 1A). 14] Its absorption spectrum presents a broad and unstructured band below 450 nm (Figure 2A). The system is luminescent in all phases, both at room temperature and at 77 K (Figure 2B) and no dependence on the solvent was observed. A summary of the photophysical properties is shown in Table 1.

Influence of the preparation method on the thiophene HDS activity of silica supported CoMo catalysts

Abstract The effect of the preparation method of CoMo/SiO2 catalysts with and without sodium ions, on the hydrodesulfurization (HDS) of thiophene was investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and N2 physisorption (BET). The samples were prepared by total sol–gel route, by classic wetness impregnation and by co-impregnation, in the presence of nitrilotriacetic acid (NTA), of commercial and sol–gel prepared silica. The influence of sodium ions added to the sol mixture and to the silica before the impregnation with Co and Mo salt solution, was also considered. The presence of sodium favoured the phase transition of amorphous silica to cristobalite with consequent reduction of the surface area and of the catalytic activity. The catalysts prepared by the sol–gel method exhibited better metal oxide dispersion but lower catalytic activity. On the contrary the catalysts supported on home-made sol–gel silica were quite active in spite of the lower surface areas and the low metal dispersion. Addition of NTA to the impregnation solution yielded better performing catalysts.

Mixed-oxide catalysts involving V, Nb and Si obtained by a non-hydrolytic sol-gel route : preparation and catalytic behaviour in oxydative dehydrogenation of propane

Abstract One-step non-hydrolytic condensation reactions, starting from VO(O i Pr) 3 and NbCl 5 , have been used for the first time to prepare Nb-V oxide catalysts. Different materials containing the NbVO 5 phase at different purity levels have been obtained, after thermal treatments, depending on the experimental conditions. The synthetic procedure has also been applied to prepare ternary Nb-V-Si oxide systems. From preliminary catalytic reaction studies it appears that the catalysts so prepared are promising with respect to their interesting performances in the oxidative dehydrogenation (ODH) of propane. It has also been found that α-Sb 2 O 4 , physically blended with the Nb-V oxide materials, could act as an appropriate promoter to improve the catalytic performances of these systems.

Ph3PSe as a convenient synthon for one-step syntheses of Ph3P-substituted selenido carbonyl iron and ruthenium clusters. Crystal structures of Fe3(μ3-Se)(μ-CO)(CO)7(PPh3)2, M3(μ3-Se)2(CO)7(Pph3)2 (MFe or Ru) and Ru4(μ4-Se)2(μ-CO)2(CO)7(PPh3)2☆

Abstract Ph3PSe reacts in toluene with Fe3(CO)12 or Ru3(CO)12 affording a variety of Ph3P-substituted selenido carbonyl clusters. In the case of iron the reaction is unselective, six products (1–6) having been obtained belonging to three different families of clusters. Fe2(μ-Se2)(CO)6−nLn (two products, 3, 5, n = 1, 2), Fe3(μ3-Se)2(CO)9−nLn (three products, 1, 2, 4, n = 0–2) and Fe3(μ3-Se)(μ-CO)(CO)9−nLn (one product, 6, n = 2). In the case of ruthenium, under certain conditions, the reaction is quite selective giving the disubstituted trinuclear cluster Ru3(μ3-Se)2(CO)7(PPh3)2 (8) in very high yield (> 90%). Minor products are the mono- and trisubstituted analogous derivatives 7 and 10 and the tetraruthenium cluster Ru4(μ4-Se)2(μ-CO)2(CO)7(PPh3)2 (9). The crystal structures of the clusters 4, 6, 8 and 9 are described.

Anchoring rhodium(I) on benzoylthiourea-functionalized silica xerogels. Production of recyclable hydroformylation catalysts and the crystal structure of the model compound [Rh(cod)(Hbztu)Cl]☆

Two benzoylthiourea-functionalized silica xerogels, 4.5SiO2 · SiO3/2(CH2)3NHC(S)NHC(O)Ph (XGbztu) and SiO3/2 (CH2)3NHC(S)NHC(O)Ph (XGbztu∗) have been prepared from (EtO)3Si(CH2)3NHC(S)NHC(O)Ph by the sol-gel process. They are able to bind rhodium(I) species giving the composite materials Rh/XGbztu and Rh/XGbztu∗, which are very active insoluble and recoverable catalysts for the hydroformylation of styrene. The anchored species undergo major changes during the catalytic cycles, particularly in the Rh/XGbztu system, whose iso/normal selectivity ratio gradually increaased in the first five runs. Futhermore, CH3(CH2)2NHC(S)NHC(O)Ph (HBztu) has been studied as a model of the surface binding function. The structure of [Rh(cod)(Hbztu)Cl]1, which represents a suitable molecular model for the anchored complexes, has been determined by X-ray diffraction.

Anchoring rhodium(I) on thiourea-functionalized silica xerogels and silsesquioxanes part II. Matrix effects on the selectivity in the hydroformylation of styrene

Abstract Three thiourea-functionalized siloxane materials, 5SiO2 · SiO3/2(CH2)3NHC(S)NHPh (XGphtu), SiO3/2(CH2)3NHC(S)NHPh (XGphtu*) and p-{SiO3/2(CH2)3NHC(S)NH}2C6H4 (XGphenditu*) were prepared. They are able to anchor Rh(I) species giving supported complexes that are very active recoverable catalysts for the hydroformylation of styrene. Some of these materials show regioselectivity variation when used in consecutive catalytic runs. The recovered catalysts have been investigated by XPS and EDX and the change in regioselectivity has been ascribed to matrix effects. In fact, the surface rhodium leaching apparently forces the catalytic process to move in the inside of the materials causing the substrate to experience the inner matrix environment. Furthermore, the non-siloxanized thioureas PhNHC(S)NHPh (Phtu) and p-{PrNHC(S)NH}2C6H4 (Phenditu), which give discrete molecular Rh(I) complexes, were studied as models for the surface binding functions. The structure of [Rh(cod)Cl(Phtu)] (cod = 1,5-cyclooctadiene) has been determined by X-ray diffraction methods.

One-step syntheses of Ph3P-substituted selenido carbonyl iron and ruthenium clusters Part 2. Crystal structures of Fe2(μ2-Se2)(CO)6-n(PPh3)n(n=1 or 2) Fe3(μ3-Se)2(CO)8(PPh3) and Ru4(μ4-Se)2(μ-CO)2(CO)8(PPh3), and HPLC behaviour of the iron derivatives

Abstract Ph 3 PSe reacts with Fe 3 (CO) 12 giving six products ( 1–6 ) belonging to three different families of clusters: Fe 3 (μ-Se 2 )(CO) 9- n L n (two products, 3,5 , n = 1, 2, Fe 3 ( μ 3 -Se) 2 (CO) 9- n L n (three products, 1, 2, 4 , n = 0–2) and Fe 3 -Se)( μ - CO ) 9- n L n (one product, 6 , n = 2). Under the same conditions, Ru 3 (CO) 12 affords Fe 3 (μ 3 -Se) 2 (CO) 9- n (PPh 3 ) n (three products 7,8,10 , n = 1–3) and the tetraruthenium clusters Ru 4 (μ 4 -Se) 4 (CO) 2 (CO) 9- n (PPh 3 ) n (two products, 11, 9 , n =1,2). The structures of the clusters 2, 3, 5 and 11 · 1 2 CH 2 Cl 2 have been determined by X-ray diffraction methods. The mass-spectral behaviour of iron mono- and disubstituted phosphine derivatives ( 2–6 ) is characterised by the low abundance (

Synthesis of diphosphine-substituted selenido carbonyl iron clusters: Progressive deformation of the Fe3Se2 core in the nido clusters [Fe3Se2(CO)7μ-(Ph2P)2R] by widening the bite of the bridging ligand

Abstract The reactions of [Fe 3 (CO) 12 ] with three diphosphine diselenides, dppmSe 2 , dppeSe 2 and dppfcSe 2 , produce the disubstituted clusters [Fe 3 (μ 3 -Se) 2 (CO) 7 (Ph 2 P) 2 R] (R = CH 2 (dppm) 3 ; R = CH 2 CH 2 (dppe) 7 ; R = (C 5 H 4 ) 2 Fe (dppfc) 8 ) as the main products. Other products are [Fe 3 (μ 3 Se) 2 (CO) 9 ] 1 , [Fe(CO) 4 (dppm)] 2 , [Fe 2 (μ-Se 2 )(CO) 4 (dppm)] 4 in the case of dppm and [Fe 3 (μ 3 -Se) 2 (CO) 8 2 (dppe)] 5 in the case of dppe. Clusters 1, 3, 5, 7 and 8 have a square-pyramidal structure with two iron and two selenium atoms alternating in the basal plane and the third iron atom (Fe ap ) at the apex of the pyramid, and should be regarded as nido -clusters with seven skeletal electron pairs. The phosphine substitution is regioselective, occurring only on the two basal iron atoms. 1 H and 31 P NMR data in solution suggest a fluxional behaviour for 3 and 7 in solution due to the migration of a metal-metal bond to link the two iron atoms bound to the bidentate ligand. This is probably related to the deformation of the Fe 3 Se 2 core induced by the steric demand of the diphosphines in such a way that the Fe ⋯ Fe non-bonding distance decreases as the bite of the ligand shortens. The crystal structures of 3, 4, 5, 7 and 8 are described.

Synthesis of MMoO4/SiO2 catalysts (M=Ni or Co) by a sol-gel route via silicon alkoxides stabilization of β-NiMoO4 at room temperature

Abstract MMoO 4 /SiO 2 composites (M=Ni or Co) were prepared by a sol–gel procedure involving Si(OMe) 4 , M(NO 3 ) 2 and (NH 4 ) 6 Mo 7 O 24 as starting materials. The dried gels were treated at increasing temperatures until crystalline grains of MMoO 4 highly dispersed in the amorphous silica matrix were formed (675°C). They were evidenced by XRD and TEM measurements. Beside supporting the MMoO 4 mixed oxide, the silica xerogel appears to play the important role of stabilizing the β-phase of nickel molybdate, which otherwise would turn into the α-phase at room temperature. The catalytic activity of the β-NiMoO 4 /SiO 2 composite in the oxidative dehydrogenation of isobutane was compared with related systems containing the metastable β-molybdate.

Easy Access to Phosphido-Selenido Clusters. Reaction of [Ru~3(CO)~1~2] with Ph~2(pyth)PSe {pyth = 5-(2-Pyridyl)-2-Thienyl} and Crystal Structure of [Ru~3(mu~3-Se)(mu-PPh~2)(mu-pyth)(CO)~6{P(pyth)Ph~2}]

The reaction of [Ru3(CO)12] with Ph2(pyth)PSe (pyth=5-(2-pyridyl)-2-thienyl) allows to obtain two novel clusters [Ru3(μ3-Se)2(CO)7{P(pyth)Ph2}2] 1 and [Ru3(μ3-Se)(μ-PPh2)(μ-pyth)(CO)6{P(pyth)Ph2}] 2 in satisfactory yields. The first one exhibits the well-known bicapped, open triangular, 50-electron nido-core, whereas 2, whose crystal structure has been determined, shows the rather rare Ru3Se tetrahedron with the Ph2P and pyth fragments as side-bridging ligands. Morever cluster 2 belongs to the exiguous family of selenido-phosphido clusters not easily achievable by other routes.