Knowledge Bank

Iron, cobalt, and nickel metal cathodes were sputtered with various mixtures of $\mathrm{<mrow\; data-mjx-texclass="ORD">37</mrow>}Cl2/15Cl2/Ar$ 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 $Fecl2$,$Fecl3$, CoCl,$CoCl2$, $CoCl3$, and $NiCl2$ The derived vibrational constants of the electronic ground state of $\mathrm{<mrow\; data-mjx-texclass="ORD">59</mrow>}Co35Cl$ are $\omega e$=457.8 $\pm$ $3.0cm-1$ and $\omega eXe$=2.0 $\pm$ $1.5cm-1$. The antisymmetric stretching mode frequencies of six isotopomers of $FeCl2$, and three isotopomers of $CoCl2$ 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 $(D3h)$ Fe and Co trichlorides and the corresponding modes of the isotopomers. These observations strongly suggest that recent data supporting a pyramidal geometry for $FeCl3$ should be reexamined. The geometry of $CoCl3$ has not previously been determined.