Synthese und Koordinationseigenschaften von Molybdocenalkoxiden – das erste Heterodimetallalkoxid mit Molybdän und Bismut

Polynuclear Bismuth-Oxo Clusters: Insight into the Formation Process of a Metal Oxide

The reaction of the bismuth silanolates [Bi(OSiR2R')3] (R = R' = Me, Et, iPr; R = Me, R' = tBu) with water has been studied. Partial hydrolysis gave polynuclear bismuth-oxo clusters whereas amorphous bismuth-oxo(hydroxy) silanolates were obtained when an excess of water was used in the hydrolysis reaction. The metathesis reaction of BiCl3 with NaOSiMe3 provided mixtures of heterobimetallic silanolates. The molecular structures of [Bi18Na4O20(OSiMe3)18] (2), [Bi33NaO38(OSiMe3)24].3 C7H8 (3.3 C7H8), [Bi50Na2O64(OH)2(OSiMe3)22].2 C7H8.2H2O (4.2 C7H8.2 H2O), [Bi4O2(OSiEt3)8] (5), [Bi9O7(OSiMe3)13].0.5 C7H8 (6. 0.5C7H8), [Bi18O18(OSiMe3)18)].2C7H8 (7. 2C7H8) and [Bi20O18(OSiMe3)24].3C7H8 (8.3C7H8) are presented and compared with the solid-state structures of [Bi22O26(OSiMe2tBu)14] (9) and beta-Bi2O3. Compound 2 crystallises in the triclinic space group P1 with the lattice constants a = 17.0337(9), b = 19.5750(14), c = 26.6799(16) A, alpha = 72.691(4), beta = 73.113(4) and gamma = 70.985(4) degrees ; compound 3.3C7H8 crystallises in the monoclinic space group P2(1)/n with the lattice constants a = 20.488(4), b = 22.539(5), c = 26.154(5) A and beta = 100.79(3) degrees ; compound 4.2C7H82 H2O crystallises in the monoclinic space group P2(1)/n with the lattice constants a = 20.0518(12), b = 24.1010(15), c = 27.4976(14) A and beta = 103.973(3) degrees ; compound 5 crystallises in the monoclinic space group P2(1)/c with the lattice constants a = 25.256(5), b = 15.372(3), c = 21.306(4) A and beta = 113.96(3) degrees ; compound 6.0.5C7H8 crystallises in the triclinic space group P1 with the lattice constants a = 15.1916(9), b = 15.2439(13), c = 22.487(5) A, alpha = 79.686(3), beta = 74.540(5) and gamma = 66.020(4) degrees ; compound 7.2C7H8 crystallises in the triclinic space group P1 with the lattice constants a = 14.8295(12), b = 16.1523(13), c = 18.4166(17) A, alpha = 75.960(4), beta = 79.112(4) and gamma = 63.789(4) degrees ; and compound 8.3C7H8 crystallises in the triclinic space group P1 with the lattice constants a = 17.2915(14), b = 18.383(2), c = 18.4014(18) A, alpha = 95.120(5), beta = 115.995(5) and gamma = 106.813(5) degrees . The molecular structures of the bismuth-rich compounds are related to the CaF2-type structure. Formally, the hexanuclear [Bi6O8]2+ fragment might be described as the central building unit, which is composed of bismuth atoms placed at the vertices of an octahedron and oxygen atoms capping the trigonal faces. Depending on the reaction conditions and the identity of R, the thermal decomposition of the hydrolysis products [Bi(n)O(l)(OH)(m-)(OSiR3)(3n-(2l-m))] gives alpha-Bi2O3, beta-Bi2O3, Bi12SiO20 or Bi4Si3O12.

Synthesis of heterometallic bismuth/molydenum alkoxides and their behavior on silica surfaces

The reaction of [(C(3)H(5))Mo(CO)(2)(CH(3)CN)(2)Cl], 2, with [Bi(OCH(2)CH(2)OCH(3))(3)](2) on a large scale leads to the novel molybdenum/bismuth alkoxide [(C(3)H(5))Mo(CO)(2)(mu-kappa O,2 kappa O'-OCH(2)CH(2)OCH(3))(2)(mu-kappa O-OCH(2)CH(2)OCH(3))BiCl], 6, as the main product as well as to [(C(3)H(5))Mo(CO)(2)(mu-kappa O,2 kappa O'-OCH(2)CH(2)OCH(3))(2)(mu-Cl)BiCl], 4, as a byproduct. Both compounds were characterized by elemental analysis, IR, and NMR spectroscopy as well as by X-ray diffraction. If 6 is brought into contact with a large excess of silica gel, aggregation and condensation reactions are initiated, which led to clusters of ca. 200 nm size spread over the silica surface. When the resulting material is calcinated at 350 degrees C in the presence of O(2), all organic ligands are eliminated and the metal oxo units rearrange: SEM/EDX measurements showed afterward Mo-free bismuth oxo clusters with sizes between 30 and 1000 nm, which are distributed together with molybdenum oxo particles of lower nuclearity over the silica surface. If such a material is employed as a potential catalyst for the propene oxidation under technical conditions, no activity is observed. If, however, the process is performed under very low pressures, a conversion of 5% is found. This result is discussed in the context of the mechanism proposed for the technical oxidation of propene to acrolein on bismuthmolybdate catalysts.