INFRARED SPECTRA OF THE MATRIX-ISOLATED CHLORIDES OF IRON, COBALT, AND NICKEL
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Date
1983
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Publisher
Ohio State University
Abstract
Iron, cobalt, and nickel metal cathodes were sputtered with various mixtures of $^{37}Cl_{2}/^{15}Cl_{2}/Ar$ to produce Ar matrices at 14 K that contained the mono-, di-, and trichlorides of the corresponding metal. The measured infrared absorption spectra of these matrices allowed the identification and characterization of $Fecl_{2}$,$Fecl_{3}$, CoCl,$CoCl_{2}$, $CoCl_{3}$, and $NiCl_{2}$ The derived vibrational constants of the electronic ground state of $^{59}Co^{35}Cl$ are $\omega_{e}$=457.8 $\pm$ $3.0 cm^{-1}$ and $\omega_{e} X_{e}$=2.0 $\pm$ $1.5 cm^{-1}$. The antisymmetric stretching mode frequencies of six isotopomers of $FeCl_{2}$, and three isotopomers of $CoCl_{2}$ were identified and measured. The dichlorides of iron, cobalt, and nickel were all determined, in contrast with previous work, to be nonlinear, with bond angles of $161^{\circ}$,$157^{\circ}$, and $161^{\circ}$, respectively. The estimated uncertainty is $5^{\circ}$. For both iron and cobalt trichlorides, the measured stretching mode frequencies were used to derive a Cl-M-Cl angle in excess of $120^{\prime}$, as would be expected for planar molecules with somewhat anharmonic vibrations. Observed adsorption peaks could be assigned to the $\nu_{3}$(E) modes of planar $(D_{3h})$ Fe and Co trichlorides and the corresponding modes of the isotopomers. These observations strongly suggest that recent data supporting a pyramidal geometry for $FeCl_{3}$ should be reexamined. The geometry of $CoCl_{3}$ has not previously been determined.
Description
Author Institution: Chemical Technology Division, Argonne National Laboratory; Department of Chemistry, Lafayette College; Department of Chemistry, Brown University