Structure and electron delocalization in Al42- and Al44-

Structure, dynamics, and electron delocalization of Al-4(2-) and Al-4(4-) based clusters are investigated. Gradient-corrected Density-Functional Born-Oppenheimer Molecular Dynamics simulations indicate that Al-4(2-) based clusters have a rigid planar Al framework, while the Al-4(4-) based moieties show large distortions from planarity. The induced magnetic field analysis of these species indicates that both systems have diatropic sigma-systems, while the pi-system is diatropic for Al-4(2-) and paratropic for Al-4(4-). The total magnetic response is diatropic for Al-4(2-), while Al-4(4-) is bitropic: it has typical antiaromatic long-range cones, while the magnetic field in the Al-4(4-) ring plane is similar to that of aromatic annulenes.