3. (20 pts) It is sometimes difficult to tell whether a ligand with more than one lone pair is donating 2 or 4e- to the metal center. The amide [NR21 ligand, on the other hand, has a structural feature (not the M-NR2 bond distance!) that usually tells one whether it is acting as a 2e- or 4e-donor. Clearly explain using simple structural diagrams (and words) the 2 and 4e- bonding modes for amide to a metal center and what the structural marker is for these two coordination types