Capped octahedral geometry

Fig. 9. The capped octahedral geometry of seven oxygens (Cs ) around Y(III) in Y(bzac)3 (OH2) complex...

Fig. 30. The capped octahedral geometry established for the Ost(CO)18 cluster. For reasons of clarity the carbonyls have been omitted.

The type-A (hexagonal) structure consists of MO7 units which approximate to capped octahedral geometry, and is favored by the lightest lanthanides (La, Ce, Pr, and Nd). Figure 18.2.1(a) shows the structure of La2C>3. 

The X-ray crystal structure of [ MoCl(CO)2(dppmSe) 2][Mo6019] 4MeN02 was reported in 1988224 by Colton et al. The molybdenum is seven-coordinate with a slightly distorted capped octahedral geometry, with a carbonyl ligand in the unique capping position. In 1991, the molecular structure of the dibromo complex [MoBr2(CO)2(i71-dppm)(7j2-dppm)] was reported.225... 

Shen and co-workers reported a method for preparing lanthanide-NHC halides through protonolysis.75 Reaction of the imidazolium bromide salt with anionic LiLn(N Pr)4 affords salicylaldiminato-functionalized NHC-lanthanide bromides (Scheme 33). The complexes were all characterised by single crystal X-ray diffraction and exhibit capped octahedral geometries. The NHC-Ln MIC bond angles decrease Nd>Sm>Er> which is consistent with decreasing ionic radii, and the Ln-NHC bond lengths also... 

The seven-coordinate phosphine complexes [W°(CO)3 Tp L]+ were prepared by oxidation of the radical species [W(CO)3Tp ] by ferroceiuum cation, followed by addition of L (PMes, PEt3, PPhs, PMe2Ph). These species exhibited capped octahedral geometries. 

Complexes [LaCl2(Tp )(L)J (L = bipy or phen) have a seven-coordinate structure with capped octahedral geometry. Reaction of [LaCl2(Tp )(bipy)] with an excess of sodium amalgam gives [La(Tp )2(bipy)], which upon oxidation with iodine forms [La(Tp )2(bipy)]I.602... 

A-type, consisting of Ln07 units which approximate to capped octahedral geometry, and favoured by the lightest lanthanides. 

The red crystalline product is sensitive to air in solution but much less so in the solid state. Solid samples show little decomposition after several days in the air but decompose to a white solid after several weeks exposure. The X-ray crystal structure shows an approximate capped octahedral geometry. The product is paramagnetic but gives a relatively sharp HNMR (CD2O2) signid at —7.9 ppm (Av,/2 4 Hz). It is soluble in dichloromethane, slightly... 

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