Isoelectronic cluster skeletal electron count

In this article we use the term isoelectronic to refer to species that contain the same total number of valence electrons. It will be necessary, however, to relax this definition for molecules that contain different sub-stitutents, e.g., Me rather than Et. Otherwise, the number of comparisons possible becomes very small. Likewise, some clusters are compared that are only isoelectronic in the sense of skeletal electron count in order to show the limits of the validity of such a separation. 

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