The ACID diagrams that take into account all π (i.e., π out and π in ) electrons in the system are shown in Fig. , from which it can be seen that the induced current intensity of these precursors is consistent with the extent of electron delocalization obtained from the previous analysis, namely C 18 -(CO) 6 < C 18 -(CO) 4 < C 18 -(CO) 2.