CHARACTERIZATION OF SOME NOVEL 1ST ROW TRANSITION-METAL CARBONYL CHLORIDES BY INFRARED AND EXAFS SPECTROSCOPY OF MATRIX-ISOLATED SPECIES

The isolation of the dichlorides of Ca, Cr, Mn, Fe, Co, Ni, and Zn in argon matrices doped with ca. 1% carbon monoxide results in a nu(CO) feature shifted to high frequency of "free" CO. In two cases (Cr and Fe) annealing caused the formation of carbonyl halides with nu(CO) at 2096 and 2110 cm-1, respectively. When the dichlorides were isolated in pure CO matrices (or argon matrices which were highly enriched in CO), in all cases except Ca (d0), Mn (d5), and Zn (d10), carbonyl halides were formed. This was demonstrated by the use of isotopic substitution and infrared spectroscopy to identify delta(MCO) and (in several cases) nu(M-C) modes. The use of isotopic and partial isotopic substitution ((CO)-C-13; (CO)-O-18) enabled the complete identification of trans-[Fe(CO)4Cl2]. EXAFS data are fully in agreement with the formulation and give the following distances: Fe-C, 1.85 (3) angstrom; Fe-0, 2.96 (4) angstrom; Fe-Cl, 2.25 (3) angstrom. On the basis of combined infrared and EXAFS data, trans-[Cr(CO)4Cl2] is also characterized. The following bond lengths were obtained: Cr-C, 2.00 (3) angstrom; Cr-O, 3.11 (5) angstrom; Cr-Cl, 2.27 (3) angstrom. For CoCl2 and NiCl2, the spectra are complicated by the presence of more than one species in the matrix, so that EXAFS data were not of assistance. In both cases, metal carbonyl halides were formed and isotopic substitution coupled with nu(M-Cl) frequencies led to the suggestion that the major species are trans-[Ni(CO)2Cl2] and trans-[CO(CO)4Cl2].