title: Structure and bonding in the isoelectronic series CnHnP5-n+: is phosphorus a carbon copy?
abstract: The relative stabilities of different isomers of the isoelectronic series C(n)H(n)P(5-n)(+) have been investigated using G3X theory. The results indicate that all species containing one or more phosphorus atom adopt a three-dimensional nido geometry, in marked contrast to the planar structure favoured by the all-carbon analogue. Within isomeric nido clusters, a strong correlation between total energy and the nucleus-independent chemical shift (NICS) indicates that three-dimensional aromaticity plays a significant role in determining the stability of the cluster. In the context of these nido clusters, the extent to which phosphorus is a carbon copy proves to be highly dependent on the global electronic environment. The first isolobal substitution of CH by P causes a complete switch from localised to delocalised bonding, accompanied by a transition from a two- to a three-dimensional structure, with the phosphorus atom showing a strong preference for the unique apical site. In contrast, further increasing the phosphorus content causes no further change in structure or bonding, suggesting that, at the basal sites, phosphorus is a rather better carbon copy. The low-energy pathways for interconversion of apical and basal atoms previously identified in C(2)H(2)P(3)(+) prove to be a general feature of all members of the series.
authors.affiliation: Department of Chemistry, University of York, Heslington, York, UK YO10 5DD. dp25@york.ac.uk
authors.forename: Dimitrios A
authors.initials: DA
authors.lastname: Pantazis
authors.forename: John E
authors.initials: JE
authors.lastname: McGrady
authors.forename: Jason M
authors.initials: JM
authors.lastname: Lynam
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Russell
authors.forename: Michael
authors.initials: M
authors.lastname: Green