“…In 2003, Lievens and co-workers [133] prepared Au 5 Zn + clusters ( Figure 54) by cationic photo-fragmentation mass spectrometry.T hey detected planar tetracoordinate Au,a nd planar tetra/pentacoordinate Zn motifs stabilized by s aromaticity. Planar tetracoordinate and pentacoordinate motifs in Ag 5 X 0,AE (X = Sc, Ti,V ,Cr, Mn, Fe, Co,and Ni) [134] and Au 5 X + (X = Au,S c, Ti,C r, Fe) [135] clusters were investigated by Lievens,Nguyen and co-workers.Frenking and co-workers [136] found that because of the strong electron delocalization, iron can adopt planar pentacoordination in FeSb 5 + and FeBi 5 + in D 5h symmetry as local minima but not global minima on the potential-energy surface.F urthermore,p lanar pentacoordinate uranium in neutral U@[c-U 5 (m 2 -C) 5 ]molecule (23 f)was predicted by Tsipis and co-workers, [60] which extends the planar motifs from transition metals into actinoids.B ut, it is not clear if this structure is ag lobal minimum or not.…”