High-valent oxo compounds of transition metals are often implicated as active species in oxygenat... more High-valent oxo compounds of transition metals are often implicated as active species in oxygenation of hydrocarbons through carbon–hydrogen bond activation or oxygen transfer and also in water oxidation. Recently, several examples of cobalt-catalyzed water oxidation have been reported, and cobalt(IV) species have been suggested as active intermediates. A reactive species, formally a dicobalt(IV)-μ-oxo polyoxometalate compound [(α<sub>2</sub>-P<sub>2</sub>W<sub>17</sub>O<sub>61</sub>Co)<sub>2</sub>O]<sup>14–</sup>, [(POMCo)<sub>2</sub>O], has now been isolated and characterized by the oxidation of a monomeric [α<sub>2</sub>-P<sub>2</sub>W<sub>17</sub>O<sub>61</sub>Co<sup>II</sup>(H<sub>2</sub>O)]<sup>8–</sup>, [POMCo<sup>II</sup>H<sub>2</sub>O], with ozone in water. The crystal structure show...
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Nanoscale cerium oxide is of increasing interest in catalysis, biomedicine, renewable energy, and... more Nanoscale cerium oxide is of increasing interest in catalysis, biomedicine, renewable energy, and many other fields. Its versatility derives from the ability to form nonstoichiometric oxides that include both Ce 3+ and Ce 4+ ions. This work describes oxidation and reduction reactivity of colloidal cerium oxide nanocrystals, termed nanoceria, under very mild solution conditions. For instance, the as-prepared nanoceria oxidizes hydroquinone to benzoquinone, with reduction of some of the Ce 4+ ions. Highly reduced nanoceria, prepared by UV irradiation in the presence of ethanol, oxidize hydroquinone back to benzoquinone. This and related reactivity allow tuning of the average cerium oxidation state in the nanocrystals without changes in size or other properties. The amounts of Ce 3+ and Ce 4+ in the nanoceria were determined both by Xray absorption spectroscopy and from the stoichiometry of the reactions, measured using 1 H NMR spectroscopy. The results demonstrate, for the first time, that the optical absorbance of nanoceria is linearly related to the percent Ce 3+ in the sample. The decrease in absorption (blue-shift of the band edge) is due to increasing amounts of Ce 3+ , not to a quantum confinement effect. These findings demonstrate the facile solution reactivity of nanoceria and establish UV−visible spectroscopy as a powerful new tool for in situ determination of Ce oxidation states in ceria nanomaterials.
Hydrogen peroxide displaces capping ligands from soluble nanoceria and forms stable surface perox... more Hydrogen peroxide displaces capping ligands from soluble nanoceria and forms stable surface peroxo/hydroperoxo species.
The crystal packing and secondary structure of H 5 PV 2 Mo 12 O 40 was followed by careful X-ray ... more The crystal packing and secondary structure of H 5 PV 2 Mo 12 O 40 was followed by careful X-ray diffraction studies that revealed four unique structures and three solid phase transitions at temperatures between 25 and 55°C, with loss of solvated water and concomitant contraction of the volume and increase of the packing density. Above 60°C H 5 PV 2 Mo 12 O 40 becomes amorphous and then anhydrous although the polyoxometalate cluster is stable indefinitely up to 300°C. Above this temperature, combined IR, Raman, XRD, and XPS measurements show the decomposition of H 5 PV 2 Mo 12 O 40 to crystalline MoO 3 and probably amorphous vanadium oxide and vanadylphosphate, the latter appearing to cover the surface of MoO 3. Importantly, H 5 PV 2 Mo 12 O 40 can be easily recovered by dissolution in water at 80°C.
High-valent oxo compounds of transition metals are often implicated as active species in oxygenat... more High-valent oxo compounds of transition metals are often implicated as active species in oxygenation of hydrocarbons through carbon-hydrogen bond activation or oxygen transfer and also in water oxidation. Recently, several examples of cobalt-catalyzed water oxidation have been reported, and cobalt(IV) species have been suggested as active intermediates. A reactive species, formally a dicobalt(IV)-μ-oxo polyoxometalate compound [(α2-P2W17O61Co)2O](14-), [(POMCo)2O], has now been isolated and characterized by the oxidation of a monomeric [α2-P2W17O61Co(II)(H2O)](8-), [POMCo(II)H2O], with ozone in water. The crystal structure shows a nearly linear Co-O-Co moiety with a Co-O bond length of ∼1.77 Å. In aqueous solution [(POMCo)2O] was identified by (31)P NMR, Raman, and UV-vis spectroscopy. Reactivity studies showed that [(POMCo)2O]2O] is an active compound for the oxidation of H2O to O2, direct oxygen transfer to water-soluble sulfoxides and phosphines, indirect epoxidation of alkenes via a Mn porphyrin, and the selective oxidation of alcohols by carbon-hydrogen bond activation. The latter appears to occur via a hydrogen atom transfer mechanism. Density functional and CASSCF calculations strongly indicate that the electronic structure of [(POMCo)2O]2O] is best defined as a compound having two cobalt(III) atoms with two oxidized oxygen atoms.
Crystallization of the {HW 9 O 33 } isopolyanion in the presence of M II (DMSO) 4 Cl 2 (where M =... more Crystallization of the {HW 9 O 33 } isopolyanion in the presence of M II (DMSO) 4 Cl 2 (where M = Ru, Os) and Na and K cations yielded one-dimensional chains, {K[HW 9 O 33 M 2-(C 2 H 6 SO) 6 ] 6-} n. The {HW 9 O 33 } isopolyanion is capped by M I-I (DMSO) 3 moieties, which are, in turn, linked by potassium cations. The chains for the Ru II-based compound show a prismatic coordination around the K + linker and {HW 9 O 33 } moieties that are eclipsed relative to each other along the chain, while the Os II-based compound has an octahedral coordination around the K + linker and {HW 9 O 33 } moieties that are staggered relative to each other along the chain. The threedimensional arrangement of the two compounds is quite different. For the Ru II compound, channels are obtained by the arrangement of six {K[HW 9 O 33 Ru 2 (C 2 H 6 SO) 6 ] 6-} n chains along the c axis. The channel is stabilized by the binding of sodium cations, which interlock the chains through coordina-[a]
High-valent oxo compounds of transition metals are often implicated as active species in oxygenat... more High-valent oxo compounds of transition metals are often implicated as active species in oxygenation of hydrocarbons through carbon–hydrogen bond activation or oxygen transfer and also in water oxidation. Recently, several examples of cobalt-catalyzed water oxidation have been reported, and cobalt(IV) species have been suggested as active intermediates. A reactive species, formally a dicobalt(IV)-μ-oxo polyoxometalate compound [(α<sub>2</sub>-P<sub>2</sub>W<sub>17</sub>O<sub>61</sub>Co)<sub>2</sub>O]<sup>14–</sup>, [(POMCo)<sub>2</sub>O], has now been isolated and characterized by the oxidation of a monomeric [α<sub>2</sub>-P<sub>2</sub>W<sub>17</sub>O<sub>61</sub>Co<sup>II</sup>(H<sub>2</sub>O)]<sup>8–</sup>, [POMCo<sup>II</sup>H<sub>2</sub>O], with ozone in water. The crystal structure show...
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Nanoscale cerium oxide is of increasing interest in catalysis, biomedicine, renewable energy, and... more Nanoscale cerium oxide is of increasing interest in catalysis, biomedicine, renewable energy, and many other fields. Its versatility derives from the ability to form nonstoichiometric oxides that include both Ce 3+ and Ce 4+ ions. This work describes oxidation and reduction reactivity of colloidal cerium oxide nanocrystals, termed nanoceria, under very mild solution conditions. For instance, the as-prepared nanoceria oxidizes hydroquinone to benzoquinone, with reduction of some of the Ce 4+ ions. Highly reduced nanoceria, prepared by UV irradiation in the presence of ethanol, oxidize hydroquinone back to benzoquinone. This and related reactivity allow tuning of the average cerium oxidation state in the nanocrystals without changes in size or other properties. The amounts of Ce 3+ and Ce 4+ in the nanoceria were determined both by Xray absorption spectroscopy and from the stoichiometry of the reactions, measured using 1 H NMR spectroscopy. The results demonstrate, for the first time, that the optical absorbance of nanoceria is linearly related to the percent Ce 3+ in the sample. The decrease in absorption (blue-shift of the band edge) is due to increasing amounts of Ce 3+ , not to a quantum confinement effect. These findings demonstrate the facile solution reactivity of nanoceria and establish UV−visible spectroscopy as a powerful new tool for in situ determination of Ce oxidation states in ceria nanomaterials.
Hydrogen peroxide displaces capping ligands from soluble nanoceria and forms stable surface perox... more Hydrogen peroxide displaces capping ligands from soluble nanoceria and forms stable surface peroxo/hydroperoxo species.
The crystal packing and secondary structure of H 5 PV 2 Mo 12 O 40 was followed by careful X-ray ... more The crystal packing and secondary structure of H 5 PV 2 Mo 12 O 40 was followed by careful X-ray diffraction studies that revealed four unique structures and three solid phase transitions at temperatures between 25 and 55°C, with loss of solvated water and concomitant contraction of the volume and increase of the packing density. Above 60°C H 5 PV 2 Mo 12 O 40 becomes amorphous and then anhydrous although the polyoxometalate cluster is stable indefinitely up to 300°C. Above this temperature, combined IR, Raman, XRD, and XPS measurements show the decomposition of H 5 PV 2 Mo 12 O 40 to crystalline MoO 3 and probably amorphous vanadium oxide and vanadylphosphate, the latter appearing to cover the surface of MoO 3. Importantly, H 5 PV 2 Mo 12 O 40 can be easily recovered by dissolution in water at 80°C.
High-valent oxo compounds of transition metals are often implicated as active species in oxygenat... more High-valent oxo compounds of transition metals are often implicated as active species in oxygenation of hydrocarbons through carbon-hydrogen bond activation or oxygen transfer and also in water oxidation. Recently, several examples of cobalt-catalyzed water oxidation have been reported, and cobalt(IV) species have been suggested as active intermediates. A reactive species, formally a dicobalt(IV)-μ-oxo polyoxometalate compound [(α2-P2W17O61Co)2O](14-), [(POMCo)2O], has now been isolated and characterized by the oxidation of a monomeric [α2-P2W17O61Co(II)(H2O)](8-), [POMCo(II)H2O], with ozone in water. The crystal structure shows a nearly linear Co-O-Co moiety with a Co-O bond length of ∼1.77 Å. In aqueous solution [(POMCo)2O] was identified by (31)P NMR, Raman, and UV-vis spectroscopy. Reactivity studies showed that [(POMCo)2O]2O] is an active compound for the oxidation of H2O to O2, direct oxygen transfer to water-soluble sulfoxides and phosphines, indirect epoxidation of alkenes via a Mn porphyrin, and the selective oxidation of alcohols by carbon-hydrogen bond activation. The latter appears to occur via a hydrogen atom transfer mechanism. Density functional and CASSCF calculations strongly indicate that the electronic structure of [(POMCo)2O]2O] is best defined as a compound having two cobalt(III) atoms with two oxidized oxygen atoms.
Crystallization of the {HW 9 O 33 } isopolyanion in the presence of M II (DMSO) 4 Cl 2 (where M =... more Crystallization of the {HW 9 O 33 } isopolyanion in the presence of M II (DMSO) 4 Cl 2 (where M = Ru, Os) and Na and K cations yielded one-dimensional chains, {K[HW 9 O 33 M 2-(C 2 H 6 SO) 6 ] 6-} n. The {HW 9 O 33 } isopolyanion is capped by M I-I (DMSO) 3 moieties, which are, in turn, linked by potassium cations. The chains for the Ru II-based compound show a prismatic coordination around the K + linker and {HW 9 O 33 } moieties that are eclipsed relative to each other along the chain, while the Os II-based compound has an octahedral coordination around the K + linker and {HW 9 O 33 } moieties that are staggered relative to each other along the chain. The threedimensional arrangement of the two compounds is quite different. For the Ru II compound, channels are obtained by the arrangement of six {K[HW 9 O 33 Ru 2 (C 2 H 6 SO) 6 ] 6-} n chains along the c axis. The channel is stabilized by the binding of sodium cations, which interlock the chains through coordina-[a]
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Papers by Delina Damatov