Exploring the Potential Energy Surface of E2P4Clusters (E=Group 13 Element): The Quest for Inverse Carbon-Free Sandwiches

Inverse carbon-free sandwich structures with formula E2P 4 (E=Al, Ga, In, Tl) have been proposed as a promising new target in main-group chemistry. Our computational exploration of their corresponding potential-energy surfaces at the S12h/TZ2P level shows that indeed stable carbon-free inverse-sandwiches can be obtained if one chooses an appropriate Group 13 element for E. The boron analogue B2P4 does not form the D4h-symmetric inverse-sandwich structure, but instead prefers a D2d structure of two perpendicular BP2 units with the formation of a double B-B bond. For the other elements of Group 13, Al-Tl, the most favorable isomer is the D4h inverse-sandwich structure. The preference for the D2d isomer for B2P 4 and D4h for their heavier analogues has been rationalized in terms of an isomerization-energy decomposition analysis, and further corroborated by determination of aromaticity of these species. Topsy turvy sandwiches: The possibility of the formation of inverse carbon-free sandwiches for clusters of type E2P4 with Group 13 elements B-Tl has been explored. This proposition is based on consideration of the aromaticity of the square-planar P4 2- unit, which should favor the formation of the cluster with a proper choice of the E + ions Moshinsky Foundation, SIP-IPN (Grants 20113309 and 20120968), and Conacyt (Grant INFRA-2012-01-188147) supported the work in Mexico. The CGSTIC (Xiuhcoalt) at Cinvestav is gratefully acknowledged for generous allocation of computational resources. Financial support from the Spanish MICINN (projects CTQ2011-23156/BQU and CTQ2011-25086/BQU), the FEDER fund (European Fund for Regional Development; grant UNGI08-4E-003), and the Generalitat de Catalunya (2009SGR637 and Xarxa de Referencia en Quimica Teorica i Computacional) is greatly acknowledged. E. M. acknowledges financial support of the EU under Marie Curie Career Integration grant (PCI09-GA-2011-294240) and the Beatriu de Pinos program from AGAUR for the postdoctoral grant (BP_B_00236). The authors are grateful to the Research Executive Agency of the European Research Council for financial support through the PIRSES-GA-2009-247671 project of the FP7-PEOPLE-2009-IRSES program. The authors thank Eloy Ramos for his helpful assistance with APOST-3D program