Interstitial nitrogen atoms

These observations point toward a permanent structural role of an interstitial nitrogen atom at the center of FeMo-co, although this is not yet proven. 

The first syntheses of carbonyl clusters containing an interstitial nitrogen atom involved the use of NO" " [Eqs. (45) and (46)] (3). In the case of rhodium, the major product was suggested to be [Rli6(CO)i4(NO)], but no further data have been reported on this. The reaction of NO with the mixture of iron carbonyls, Fe(CO)s and [Fe2(CO)8] , yielded two clusters... 

Now there are quite a few clusters like [CoioN2(CO)i9] , that contain more than one interstitial nitrogen atom but they are known only for cobalt and rhodium. As can be seen in Table 3 they all are derived from nitrido precursors, mostly [Co6N(CO)i5] (1) or [Rh6N(CO)i5 (2), and are generally produced by thermal activation. Scheme 1 may help to illustrate the different behavior of the Co and Rh compounds. 

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