CO as an IRprobe molecule for characterization of copper ions in a basolite C300 MOF sample

Abstract

The state of the accessible copper ions in a Cu-basolite C300 sample (copper benzene-1,3,5-tricarboxylate) was studied by CO as an IR probe molecule. Low temperature CO adsorption on a sample activated at 473 K results in a series of carbonyl bands. Three intense sharp bands at 2141, 2128 and 2123 cm⁻¹ are very sensitive to the CO equilibrium pressure and are associated with CO polarized by the aromatic ring. Three bands, at ca. 2192, 2178 and 2148 cm⁻¹ are assigned to three different kinds of monocarbonyl species. At high CO coverage, the principal carbonyls (2178 cm⁻¹) are converted into polycarbonyls. A band at 2125 cm⁻¹ (resistant to evacuation) is associated with Cu⁺ ions on small CuO particles. Experiments on ¹²CO–¹³CO adsorption revealed lack of vibrational coupling and also showed that the bands at 2192 and 2148 cm⁻¹, although changing almost in concert, were due to individual species. Sample activated at 373 K does not contain copper oxide, which indicates that activation at higher temperatures, 473 K, leads to some irreversible changes.