Cobalt dinitrosyl

Based on previous studies [15, 22-25], the band at 1941 cm-i is assigned to Co2+(NO), and the pair of bands at 1894 and 1815 cm-i, to Co2+(NO)2- The shoulders at 1874 and 1799 cm may be due to a second dinitrosyl species. While little is known about the location and coordination of the Co 2+ in ZSM-5, it is likely that cobalt ions are associated with both [Si-0-Al]- and [Al-0-Si-0-AI]2- structures in the zeolite. In the former case, the cobalt cations are assumed to be present as Co2+(OH-) cations and in the latter case as Co2+ cations. The presence of cobalt cations in different environments could account for the appearance of two sets of dinitrosyl bands. The band at 2132 cm-> is present not only on Co-ZSM-5 but also on H-ZSM-5 and Na-ZSM-5, and has been observed by several authors on Cu-ZSM-5 [26-28]. 

The cobalt analog of the iron dinitrosyl iodide is prepared according to the above procedure with only minor modifications, which are outlined below. Anhydrous deoxygenated reagent-grade acetone and 35.4 g. of cobalt powderf are added to the 1000-ml. flask and allowed to react with the ether solution of iodine (38.1 g. (0.15 mole) of iodine in 300 ml. of ether) over a period of 30 minutes. Then nitric oxide is admitted to the flask. The reaction... 

After formation of the dinitrosyl, the sample was evacuated at elevated temperatures and the valence state of cobalt probed again with CO. After such a treatment a new EPR signal was once again observed (Figure 1.23C) with the spin Hamiltonian parameters ofg, = 2.199, g, = 2.119, = 1.973, A = 48, Aj, = 125,... 

Dinitrosyl Cobalt Halides (NO)2CoC1, (NO)2CoBr, (NO)2CoI... 

Adsorbed NO can be even more sensitive than adsorbed CO to the oxidation state of the cations for example, the use of NO as a probe allows the determination of the oxidation state of Co ions in zeolites better than CO. On a Co-ZSM5 zeolite, three bands due to adsorbed CO are observed at 2,204, 2,198 and 2,188 cm b they are due to different cobalt carbonyls but it is difficult to assign them the oxidation state for cobalt. When NO is used as the probe it shows the existence of both Co " " and Co + species. In fact the bands observed at 1,901, 1,817 cm are due to [Co(NO)2] gem—dinitrosyl species while that at 1,945 cm is assigned to [Co-NO] + mononitrosyls. 

Nitrogen oxide (NO) interacts strongly with the coordinatively unsaturated cations of oxide surfaces than CO does. Characteristic of NO is the formation of dinitrosyl species, i.e., two NO molecules attached to the same metal ion, on many oxide surfaces, such as those of the catalytically relevant oxides of molybdenum, tungsten, iron, cobalt, and chromium. 

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