“…Thermal Behavior of [Os 3 (CO) 10 ( μ -H)( μ -OSiEt 3 )] as a Model of the Thermal Degradation of Silica-Anchored [Os 3 (CO) 10 ( μ -H)( μ -OSi ⋮ )] (Scheme ). Metal clusters supported on inorganic oxides constitute an interesting class of hybrid materials, and their use as catalyst precursors may provide activities and selectivities often different from those displayed by the usual supported metallic catalysts. − Since a thermal treatment of these materials is generally required to promote their catalytic activity, this aspect cannot be limited to the evidence of thermal rearrangements of surface species, but it may involve a complex surface organometallic chemistry originated by reaction with the OH groups of the support. ,−, With silica-supported [Os 3 (CO) 12 ], it is now well established that thermal treatment (at 100−150 °C) causes, as the first step of chemisorption, oxidative addition of a surface silanol group into an Os−Os bond of the triangular frame with formation of silica-anchored [Os 3 (CO) 10 (μ-H)(μ-OSi⋮)]. ,, Further thermal treatment (at 150−250 °C) leads to new surface species of interest in view of their catalytic activity; 10b,, however, their nature has been, as already pointed out, the subject of some controversy. ,−,− 2 Thermal Degradation of [Os 3 (CO) 10 (μ-H)(μ-OSiEt 3 )] …”
The reactivity (e.g., toward hydrolysis, alcoholysis, reduction by CO or H2) of various [Os3(CO)10(μ-H)(μ-OSiPh2R‘)] (R‘ = Ph, OH, OSiPh2OH) clusters and the thermal behavior of
[Os3(CO)10(μ-H)(μ-OSiEt3)] have been studied with the aim of clarifying by a molecular
approach some aspects of the surface chemistry of silica-anchored [Os3(CO)10(μ-H)(μ-OSi⋮)].
Their easy and selective reduction to [Os3(CO)12] (under CO) and to [H4Os4(CO)12] (under
H2) suggests that [Os3(CO)10(μ-H)(μ-OSi⋮)] does not require, as a reactive intermediate, a
previous hydrolysis to the more reactive molecular species [Os3(CO)10(μ-H)(μ-OH)] in order
to generate different osmium carbonyl clusters in their silica-mediated synthesis starting
from OsCl3 or [Os(CO)3Cl2]2. The thermal behavior of [Os3(CO)10(μ-H)(μ-OSiEt3)] dissolved
in triethylsilanol (to mimic a silica surface with many available surface silanols) or triglyme
(to mimic a highly dehydroxylated silica surface) gives an answer to the controversy on the
nature of the products formed by thermal degradation on the silica surface of [Os3(CO)10(μ-H)(μ-OSi⋮)]. In triethylsilanol, oxidation occurs to give a Os(II) hydrido carbonyl species
which, on the basis of chemical and spectroscopic evidence, we suggest to be [Os(CO)3(μ-OSiEt3)2(OSiEt3)(H)Os(CO)2]
n
(n = probably 2), whereas in triglyme an aggregation to high-nuclearity clusters such as [H4Os10(CO)24]2- and [H5Os10(CO)24]- occurs. Therefore, it is shown
for the first time that molecular models not only are a tool to define structural aspects but
also may be a springboard to understand and clarify by a molecular approach aspects of the
reactivity of organometallic species on the silica surface.
“…Thermal Behavior of [Os 3 (CO) 10 ( μ -H)( μ -OSiEt 3 )] as a Model of the Thermal Degradation of Silica-Anchored [Os 3 (CO) 10 ( μ -H)( μ -OSi ⋮ )] (Scheme ). Metal clusters supported on inorganic oxides constitute an interesting class of hybrid materials, and their use as catalyst precursors may provide activities and selectivities often different from those displayed by the usual supported metallic catalysts. − Since a thermal treatment of these materials is generally required to promote their catalytic activity, this aspect cannot be limited to the evidence of thermal rearrangements of surface species, but it may involve a complex surface organometallic chemistry originated by reaction with the OH groups of the support. ,−, With silica-supported [Os 3 (CO) 12 ], it is now well established that thermal treatment (at 100−150 °C) causes, as the first step of chemisorption, oxidative addition of a surface silanol group into an Os−Os bond of the triangular frame with formation of silica-anchored [Os 3 (CO) 10 (μ-H)(μ-OSi⋮)]. ,, Further thermal treatment (at 150−250 °C) leads to new surface species of interest in view of their catalytic activity; 10b,, however, their nature has been, as already pointed out, the subject of some controversy. ,−,− 2 Thermal Degradation of [Os 3 (CO) 10 (μ-H)(μ-OSiEt 3 )] …”
The reactivity (e.g., toward hydrolysis, alcoholysis, reduction by CO or H2) of various [Os3(CO)10(μ-H)(μ-OSiPh2R‘)] (R‘ = Ph, OH, OSiPh2OH) clusters and the thermal behavior of
[Os3(CO)10(μ-H)(μ-OSiEt3)] have been studied with the aim of clarifying by a molecular
approach some aspects of the surface chemistry of silica-anchored [Os3(CO)10(μ-H)(μ-OSi⋮)].
Their easy and selective reduction to [Os3(CO)12] (under CO) and to [H4Os4(CO)12] (under
H2) suggests that [Os3(CO)10(μ-H)(μ-OSi⋮)] does not require, as a reactive intermediate, a
previous hydrolysis to the more reactive molecular species [Os3(CO)10(μ-H)(μ-OH)] in order
to generate different osmium carbonyl clusters in their silica-mediated synthesis starting
from OsCl3 or [Os(CO)3Cl2]2. The thermal behavior of [Os3(CO)10(μ-H)(μ-OSiEt3)] dissolved
in triethylsilanol (to mimic a silica surface with many available surface silanols) or triglyme
(to mimic a highly dehydroxylated silica surface) gives an answer to the controversy on the
nature of the products formed by thermal degradation on the silica surface of [Os3(CO)10(μ-H)(μ-OSi⋮)]. In triethylsilanol, oxidation occurs to give a Os(II) hydrido carbonyl species
which, on the basis of chemical and spectroscopic evidence, we suggest to be [Os(CO)3(μ-OSiEt3)2(OSiEt3)(H)Os(CO)2]
n
(n = probably 2), whereas in triglyme an aggregation to high-nuclearity clusters such as [H4Os10(CO)24]2- and [H5Os10(CO)24]- occurs. Therefore, it is shown
for the first time that molecular models not only are a tool to define structural aspects but
also may be a springboard to understand and clarify by a molecular approach aspects of the
reactivity of organometallic species on the silica surface.
“…Steel and medicine tablets samples were prepared as described previously. 25 Recovery data for Cu in steel solution and medicine tablets are given in Tables 2 and 3, respectively. The recovery was found to be 77-94%.…”
Section: Applications Of the Methods Determination Of Cu In Steel Sam...mentioning
confidence: 99%
“…The average values of D of each metal (mL g 21 ) in the concentration range of 3 . 0610 25 -1 . 35610 23 mmol mL 21 , are found to be: Cu 2 .…”
Section: Adsorption Isothermsmentioning
confidence: 99%
“…Surface chemistry is a field of increasing importance in various fields like immobilised polymeric resins, heterogeneous catalysis, 25 etc.. One of the objectives of research in this field is to study elementary steps of reactions on the surface. If a single structure or several closely related structures are formed on the surface, then it becomes possible to use stoichiometric reactions to characterise the reactivity of these surface species.…”
Section: Molecular Modelling Studies On Silica Surface Chemically Mod...mentioning
A surface modified silica gel chelating resin was synthesised by immobilising tetracycline (TCN) on the surface of modified silica gel to produce a granular sorbent for the adsorption and estimation of copper, nickel and cadmium. Metal ions were quantitatively retained on the column packed with immobilised silica gel in the pH ranges of 5 . 0-6 . 5 for Cu, 6 . 8-7 . 8 for Ni and 6 . 6-7 . 8 for Cd. The distribution coefficient D determined for each metal ion was as follows (mL g 21 ): Cu, 2 . 45610 2 ; Ni, 1 . 84610 2 ; Cd, 2 . 33610 2 . Methods have been developed to determine copper, nickel and cadmium in steel, medicine tablets, alloys and river water samples. Molecular modelling studies were also performed on TCN-imobilised silica gel for gaining an insight into the active structure of TCN on the silica surface.
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