Cerium complexes structures

Two other dimeric complexes which are related in structure to [Yb-(C5H4(CH3))2C1]2 are [Ce(C8H8)Cl 2THF]2 and [Sc(C5H5)2Cl]a. The cerium complex was discussed earlier. The structure of the scandium complex 118) is the same as that in Fig. 11. For the planar unit with symmetrical bridges, changing... 

The structure of the cerium complex [162] consists of a centrosymmetric tetranuclear unit with a doubly metallated Cp group with r 5, rf, ij C5(CH2)2Me3 shared between three Ce atoms. 

In the cerium complex an unusual 12-membered ring has been observed. The ring is formed by Ce-0=C-W units with the O-C-W angle nearly linear (178°) while the Ce-O-C angle is 154°. This structure has been found to be unstable [258]. 

A number of crystal structures of derivatives containing the [Eu(dik)4] are available but, at variance with the cerium complexes, the electrochemical investigation of a number... 

The reactions of LnCls with only one equivalent of K2C8H8, carried out in THF, afford complexes of the type [C8H8LnCl(THF)2]2 (105,111, 112). The investigation of the structure of the cerium complex proves the dimeric nature and shows the two cerium atoms bridged asymmetrically by the two chlorine atoms,and, in each case, coordinated by one cyclooctatetraenyl ring and two THF molecules (113). The complexes loose THF upon heating to 60 C in vacuo. The lutetium compound reacts with alkyl-lithium compounds with formation of the first cyclooctatetraenyl(organ-yl)lutetium compounds (11 ) ... 

The green cerium complex was characterized by elemental analysis and infrared spectrum. The structure of this complex is not known, but its... 

In this complex, the bis([8]annulene)cerate(II) complex is formally a dianion. The cerium complex as its di(l,2-dimethoxyethane) adduct was characterized by elemental analysis and infrared spectrum. The structure of [K(C Hjq02)]2[Ce(CgHg)2] is not known, but the infrared spectrum of the cerium complex does contain bands (887 and 682 cm-i) which are consistent with the presence of an [8]annulene dianion.S7 Although there are reports of Ce(II) from the reduction of Ce(III) in other systems,58,59 the presence of the cerium(II) ion in... 

Ce(acac)3 may be used instead of isopropoxide, but in this case the obtained product is less pure. The cerium complex is crystallized from the reaction mixture as black needles. The compound is pyrophoric and slowly decomposed by deaerated water. Its structure has been confirmed by the data of elemental analysis, IR-, NMR and mass spectrometry (the molecular ion is present in the spectrum) and the preliminary X-ray data. 

Binuclear complexes of Ln(III) of general formula [(CgHg)2Ln][(CgHg)Ln(THF)2] (Ln Ce, Nd, Er) are formed on the condensation of these metal vapours at cyclooctatetraene at -196°C [24]. Besides, the cerium complex of the same structure has been prepared according to the reaction [35] ... 

The biscyclooctatetraene complexes have similar properties, are colored, decompose when heated above 160°C under vacuum, and do not sublime even at 1 X 10 mm. However, they are thermally stable when heated to 360 C in sealed tubes under one atmosphere of argon. They are insoluble in CHCI3, CCI4, and hexane, and are moderately soluble in THF and dioxane. The molecular structure of the cerium complex has been determined (Hodgson and Raymond, 1972b) and is shown in fig. 25.24. The important feature is the symmetric coordination of the two CgHi rings in a 7r-fashion. The molecular symmetry is very close to Dgd-... 

The crystal structure of the cerium sandwich complex (31) (34) shows it to be similar to that of the related Cclv bis(octaethylporphyrinate) complex (Fig. 7) (83, 84). 

The geometry at cerium is distorted square antiprismatic with a mean stagger of -28°, a value noticeably less than that (42°) observed in the porphyrin complex. The Ce-N distances are in the range 2.411(9)-2.430(9) A, distances that are markedly shorter than those in the porphyrin structure that range between 2.467(3) and 2.483(3) A (Fig. 8). 

Catalysts. In industrial practice the composition of catalysts are usually very complex. Tellurium is used in catalysts as a promoter or structural component (84). The catalysts are used to promote such diverse reactions as oxidation, ammoxidation, hydrogenation, dehydrogenation, halogenation, dehalogenation, and phenol condensation (85—87). Tellurium is added as a passivation promoter to nickel, iron, and vanadium catalysts. A cerium tellurium molybdate catalyst has successfully been used in a commercial operation for the ammoxidation of propylene to acrylonitrile (88). 

The coordination geometry in anhydrous Th(CF3COCHCOMe)4 is a 1111 ( )4-422) antiprism 74 the structure of the monohydrate has been discussed earlier (p. 1144). Th[CF3COCHCO(2-C4H3S)]4 is isostructural with the cerium(IV), uranium(IV) and plutonium(IV) analogues. The coordination polyhedron is a distorted dodecahedron in which the four ligands span the two perpendicular trapezoids of the dodecahedron.75 In the complexes M(n-C3F7COCHCOBut)4, the thorium(IV), uranium(IV) and neptunium(IV) compounds are isomorphous, but the plutonium compound is not. 

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