Isoelectronic clusters with the same basic cage structures may exhibit surprisingly different magnetic properties. For instance, nucleus-independent chemical shift (NICS) values, computed at cluster centers, may range considerably in magnitude and even change from diatropic to paratropic. The same is true for dissected canonical molecular orbital contributions to the total NICS values, computed by the GIAO method. Thus, HOMO-NICS values are paratropic only if the HOMO->LUMO rotational transition is allowed by symmetry selection rules derived from group theory. High symmetry inorganic cages are likely to exhibit spherical aromaticity if the HOMO->LUMO rotational transition is forbidden by these symmetry rules. Otherwise, inorganic clusters will exhibit paratropicity if this is not weakened by the insufficient overlap between the HOMO and the rotated LUMO and by a very appreciable energy difference between them. Larger cages, such a Au20 (Td), with many electrons and bonding MOs, are expected to be diatropic.
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