No abstract

The goal of this work was to prepare structurally well-defined manganese complexes on high-area MgO powder by vapor deposition of Mn 2 (CO) 10 . The supported species were characterized by infrared (IR), electron paramagnetic resonance (EPR), and X-ray absorption spectroscopies. The results show that when the manganese loading of the sample was 3.0 wt %, most of the Mn 2 (CO) 10 was physisorbed, but when the loadings were less, chemisorbed species predominated, being formed by adsorption of Mn 2 (CO) 10 on hydroxyl groups on the MgO surface. Treatment of samples containing 1.0 wt % Mn with O 2 at room temperature resulted in oxidation of the manganese and the formation of surface species that are well represented as the d 4 complex Mn(CO) 3 (O s ) 3 (where O s is surface oxygen of MgO), as indicated by IR and extended X-ray absorption fine structure (EXAFS) spectra. The EXAFS data show Mn-C, CtO, and Mn-O s bond lengths as 1.90, 1.43, and 1.98 Å, respectively.

MgO-supported manganese carbonyl complexes were prepared by chemical vapor deposition of Mn(CO)5CH3 on partially dehydroxylated, high-area MgO powder. X-ray absorption spectra identify the resultant surface species, on average, as Mn(CO)4(Os)2 (where the two oxygen ligands are part of the MgO surface), and infrared spectra show that the chemisorption results from the reaction of Mn(CO)5CH3 with OH groups of the MgO surface. Electron paramagnetic resonance and X-ray absorption near edge data indicate that the manganese was in a positive oxidation state other than +2, but the value is not determined, and the IR spectra indicate the presence of a mixture of manganese carbonyls. Extended X-ray absorption fine structure spectra determine the average Mn-CO bond distance to be 1.87 Å and the average Mn-O bond distance to be 2.12 Å. The surface complex was found to be stable in O2 at room temperature.