Bridging chlorines

Zirconium tetrachloride is a tetrahedral monomer in the gas phase, but the soHd is a polymer of ZrCl octahedra arranged in zigzag chains in such a way that each zirconium has two pairs of bridging chlorine anions and two terminal or t-chlorine anions. The octahedra are distorted with unequal Zr—Cl bridge bonds of 0.2498 and 0.2655 nm. The physical properties of zirconium tetrachloride are given in Table 7. 

R = R2 = R3 = R4 = R5 = Me] also reacts with [(i -C2H4)2RhCl] to give the tetranuclear product 3 formulated as a pentadecker species with two central bridging chlorine atoms. 

Fig. 24. Asymmetric unit of M03S7CI4, including bridging chlorine atoms. (Redrawn from J. D. Marcoll, A. Rabenau, D. Mootz, and M. Wunderlich, Rev. Chim. Miner. 11, 607 (1974), Fig. 4, p. 613.)...

Fig. 5.4 View of the structure and intercluster connectivity of the [(ZreBjClia] structure, and mixed halide derivative, respectively. Edge-bridging chlorines are...

The bridging chlorine atoms (2 lone electron pairs) should have bond angles smaller than 109.5° but larger than 90°. The angle at the metal atom in the four-memberedring is forced to a value under 90° it adopts 78.6°. The outer, equatorial Cl atoms now experience a reduced repulsion, so that the angle between them is enlarged from 90° to 101.2°. Due... 

Examinations of the far-infrared spectra of solutions of Zr (allyl) 3CI and Zr (allyl) 2CI2 (9) suggest that the former exists in solution as the dimer (X), whereas the latter has the monomeric structure (XI). A broad intense peak at 244 cm-1 can be assigned to zirconium-bridging chlorine stretching mode. This band is completely absent from the spectrum of the dihalide and is replaced by a very strong band at 342 cm-1 due to the nonbridging chlorine. 

Reaction of 3 with 1 equivalent of a phosphine results in formation of "phosphine-modified catalysts (4). The complex formed from 7r-allyl-nickel chloride, tricyclohexylphosphine, and methylaluminum dichloride (4a) has been isolated and its structure determined crystallographically (see Fig. 1) (57) The phosphine is bonded to the nickel atom, and interaction with the Lewis acid takes place via a chlorine bridge. The bridging chlorine atom is almost symmetrically bound to both the nickel... 

The experimental data for the Fe2Cl6 molecules could be best approximated by a model with a puckered four-membered ring (Cjy symmetry). However, the deviation from the Z)2h symmetry may be a consequence of large-amplitude vibrations around the imaginary axis connecting the two bridging chlorine atoms (cf. 

The picture of the nitrogen atoms in diazadiboretidines acting as Lewis base centers is also supported by the formation of a 1 1 coordination compound with TiCl4 [Eq. (58)] (91). The B-NMR signal of 22.7 ppm indicates a highfield shift, which cannot be due to d-electrons from tetravalent d -titanium. X-Ray structural analysis shows that bridging chlorine atoms provide the observed electronic saturation of the boron atoms. 

The bridging chlorine atoms in these ir-allylicpalladium complexes are readily replaced by bromine, iodine, or the thiocyanate group by treatment with the corresponding alkali metal salt in a suitable solvent such as acetone 105, 194). The chlorine bridge is split by amines for example, the ir-allyl complex [PdCl(7r-CsH6)]2, with p-toluidine, gives [PdCl(7r-C3H6) (p-tolui-dine)] as stable, pale yellow crystals (105). 

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