Bond distances cyclooctatetraene

FIGURE 11 12 Molecular geometry of cyclooctatetraene The ring is not planar and the bond distances alternate between short double bonds and long single bonds... 

The binuclear iron complex (C8H8)Fe2(CO)6 had been expected from the reaction, but the chair conformation (XXXV), which was subsequently found for this substance, was entirely unexpected (65j 66j 67). In this complex, each end of the cyclooctatetraene ligand behaves as a butadiene-type (n = 4) ligand, and bond distance measurements indicate very little tt-tt interaction between the two halves of the ring. The proton NMR spectrum of the complex in solution exhibits two resonances of equal intensity, while the infrared spectrum is very similar to the spectrum of butadiene-iron tricarbonyl and similar diene complexes (105). 

The dication adopts a three-legged piano-stool configuration in which the O-U-O angles vary from 84.0° to 88.2° with a mean value of 87(3)°, and average COT-U-O angles of 127(1)°. The uranium atom is 1.92(2) A away from the planar cyclooctatetraene ring, and the mean U-G bond distance is 2.65(3) A. These values compare well with those determined in the monocationic cyclooctatetraene complexes [(COT)U(NEt2)(THF)3]+.161... 

Crystallographic data, bonding distances and angles in rare earth cyclooctatetraene complexes. 

A very similar study has been performed on the complex formed from silver nitrate and cyclooctatetraene 12,13). This polymeric complex is obtained by reaction of aqueous silver nitrate with cyclooctatetraene dissolved in petroleum ether. Like the benzene-silver perchlorate described above, this complex decomposes readily and hence was examined in an atmosphere of the ligand. Complete bond distance and angle data are available for its structure as shown in Table V.l 13). The molecular structure of the 1 1 silver nitrate-cyclo-octatetraene dimer has been determined by X-ray crystallographic analysis 15). 

Fig. 2. The structure of cyclooctatetraene-iron tricarbonyl, after Dickens and Lipscomb. The C—C bond distances of the diene-Fe(CO)s unit are each 1.42 A.

The vanadium—vanadium bond length in the organometallic complex ( 5-C5H5)2V2(C4H8)2 (Figure 9) of 2.315(1) A is somewhat controversial.31 32 Similar to /i-( 5 5-cyclooctatetraene)bis[( p-cyclopentadienyl)divanadium]33,34 with a metal-metal distance of 2.439(1) A, the interpretation of the interaction between the two vanadium centers has been proposed to be a triple bond, a very short single bond,33 or a weak double bond.35... 

Estimate interelectronic repulsion in the cyclooctatetraene dianion due to the interaction of the two charges only (use the benzene bond length and a reasonable average for the interelectronic distance). 

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