| | 1 | Author
| Peter Morys, Sabine Schmerbeck | Requires cookie* | | | Title
| Über die Photolumineszenz von Oberflächenverbindungen des Molybdäns auf Silicagel On the Photoluminescence of Molybdenum Surface Compounds on Silicagel Supports  | | | | Abstract
| The UV induced photoluminescence (PL) of activated and reduced surface molybdenum com-pounds on silica gel has been studied at various concentrations of the products under He and Ar and at various temperatures from R.T. to 10 K. With the activated molybdenum(VI) compounds, four different types of broad band emissions were observed and assigned to definite surface species of Mo(VI): A blue PL occurring mainly at T > -90 °C, two "white" emissions with different spectral excitation regions and Stokes shifts appearing very strongly under He or vacuum below T < —90 °C and a yellow PL occurring with the products under Ar, N 2 or C0 2 instead of the "white" ones. While the blue PL was ascribed to an octahedrally coordinated surface species (Moc 1), the two "white" emissions were attributed to two tetrahedrally coordinated surface species, the first one (MoX 1) being monomeric and bonded directly to the surface, the second one (Mo^ 1) being bonded to a polymolybdate cluster and excited via that cluster; the yellow PL was postulated to originate from a MOB 1 —Ar Van der Waals complex. At 10 K the "white" PL of the polymeric MOB 1 species showed a faint vibronic fine structure; the emission time constant was measured to be 5 ms. With the reduced compounds, only one PL was observed attributable to the monomeric MoX 1 species. Hence this species was concluded to be the only one not or not completely being reducible. | | | |
Reference
| Z. Naturforsch. 42b, 756—763 (1987); eingegangen am 16. Januar 1987 | | | |
Published
| 1987 | | | |
Keywords
| Luminescence, Surface Compounds, Molybdenum Compounds | | | |
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| default:Reihe_B/42/ZNB-1987-42b-0756.pdf | | | | Identifier
| ZNB-1987-42b-0756 | | | | Volume
| 42 | |
| 2 | Author
| B. Moeseleb, D. Horvath, Lindenau, H. L. Krauss | Requires cookie* | | | Title
| R | | | | Abstract
| Oxygen The oxygen partial pressure above sup-ported, coordinatively unsaturated Cr 11 , V 111 , Mo 11 and Mn 11 species was measured with a Zr02 cell. Within this series the pressure ranges from 10~ 6 to 10 -11 ppm 02, with the Mn n /Si02 systems exhibiting the lowest values of 10~ 10 -8 and 10" 11 -3 . Other pertinent properties like chemiluminescence with 02 and catalytic activity in ethylene polymerisa-tion are also indicated. The manganese(II) absorption masses are thus particularly suitable for removal of traces of oxygen from liquids and gases in general but especially from polymerizable olefins. | | | |
Reference
| (Z. Naturforsch. 31b, 892—893 [1976]; eingegangen am 12. März 1976) | | | |
Published
| 1976 | | | |
Keywords
| Absorption, Surface Compounds, Transition Metals, Coordinative Unsaturation, Supports | | | |
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| default:Reihe_B/31/ZNB-1976-31b-0892_n.pdf | | | | Identifier
| ZNB-1976-31b-0892_n | | | | Volume
| 31 | |
| 3 | Author
| Hans-Ludwig Krauss, Ulrich Westphal | Requires cookie* | | | Title
| Oberflächenverbindungen von Übergangsmetallen, XX [1] Komplexe von Oberflächen-Chrom(II) mit Olefinen Surface Compounds of Transition Metals, XX [1] Complexes of Surface Chromium(II) with Olefines | | | | Abstract
| Surface chromium(II) supported on silica forms 1:1 and 1:2 complexes with defines; polyenes prefer chelate structures. For the ligand-to-metal bond a "Zeise-Salt" type is postulated. Secondary reactions include cis-trans isomerisation, shift of double bond, rearrangement of C-framework and polymerization/oligomerization. Cyclopentadiene obviously gives a h 5 -cyclopentadienyl/hydrogen complex by oxidative addition followed by H2 emission and formation of a h 5 -cp-Cr m complex; in this case the metal can be split off from the support by H+ without cleavage of the cp-Cr-bond. Einführung und Problemstellung | | | |
Reference
| Z. Naturforsch. 33b, 1278—1284 (1978); eingegangen am 31. Juli 1978 | | | |
Published
| 1978 | | | |
Keywords
| Surface Compounds, Olefine Complexes, Cyclopentadienyl Complexes, Chromium(II) Complexes, Isomerisation | | | |
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| default:Reihe_B/33/ZNB-1978-33b-1278.pdf | | | | Identifier
| ZNB-1978-33b-1278 | | | | Volume
| 33 | |
| 4 | Author
| Hans-Ludwig Krauss, Erich Hums | Requires cookie* | | | Title
| Oberflächenverbindungen yon Übergangsmetallen, XXIII [1] Die Umsetzung cyclischer Olefine mit Oberflächen-Chrom(II) auf Silicagel bei höherer Temperatur Surface Compounds of Transition Metals, XXIII [1] The Reaction of Cycloolefines with Surface Chromium (II) on Silicagel at Higher Temperature | | | | Abstract
| By reaction with surface chromium(II) on silicagel at T > 150 °C, cycloolefins can undergo ring contraction, methylation/demethylation, hydrogenation/dehydrogenation, and iso-meri7ation. Furthermore, n-alkanes (Ci... C4) are formed incorporating support hydrogen. -As in the case of the corresponding acyclic olefins, a common intermediate MC3 (metalla-cyclobutane^HM-allyl complex) for all these reactions is postulated; the transfer of Ci units is claimed to proceed via a carbene M = CH2 derived from the MC3 precursor. | | | |
Reference
| Z. Naturforsch. 35b, 848—854 (1980); eingegangen am 21. Februar 1980 | | | |
Published
| 1980 | | | |
Keywords
| Surface Compounds, Ring Contraction, Methylation/Demethylation, Hydrogenation/Dehydrogenation, Carbene Intermediates | | | |
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| default:Reihe_B/35/ZNB-1980-35b-0848.pdf | | | | Identifier
| ZNB-1980-35b-0848 | | | | Volume
| 35 | |
| 5 | Author
| Hans-Ludwig Krauss, Erich Hums | Requires cookie* | | | Title
| Oberflächenverbindungen von Übergangsmetallen, XXII [1] Die Umsetzung von Oberflächen-Chrom(II) auf Silicagel mit Olefinen bei höherer Temperatur. - Zum Mechanismus von Aufbau-, Abbau-, Metathese- und Isomerisierungs-Reaktionen an koordinativ ungesättigten Oberflächen-Metallionen Surface Compounds of Transition Metal, XXII [1] The Reaction of Surface Chromium(II) on Silica with Olefins at Higher Temperature. - A Contribution to the Mechanism of Growth, Degradation, Metathesis and Isomerization on Coordinatively Unsaturated Surface Metal Ions | | | | Abstract
| With chromium(II) supported on silica, at T > 150 °C olefins undergo growth/degra-dation/metathesis reactions by addition/elimination of even and uneven chain fragments including Ci. Simultaneously, catalytic double bond isomerization and C-rearrangements to methyl branched olefins occur. One mechanism is proposed for all these reactions via a pseudo-tetrahedral MC3 intermediate. Polyethylene synthesis at lower temperatures may follow the same way. For growth/degradation/metathesis the formation of a metal carbene unit is postulated as a characteristic step; in case of ethylene, >Cr=CH2 will be formed as a precursor of the final CH4 (resulting from a secondary reaction with support hydrogen). | | | |
Reference
| Z. Naturforsch. 34b, 1628—1636 (1979); eingegangen am 23. Juli 1979 | | | |
Published
| 1979 | | | |
Keywords
| Surface Compounds, Olefin Polymerization/Degradation, Olefin Metathesis, Olefin Isomerization, Carbene Intermediates | | | |
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| default:Reihe_B/34/ZNB-1979-34b-1628.pdf | | | | Identifier
| ZNB-1979-34b-1628 | | | | Volume
| 34 | |
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