Octahedral aromaticity in 2S+1A1g X6q clusters (X = Li-C and Be-Si, S = 0-3, and q = −2 to +4)

It is generally observed that quintessential aromatic compounds have delocalised electronic configurations that are of closed-shells or open-shells half-filled with the same spin electrons. Guided by this property, we search for aromatic octahedral clusters of the type X6q (X = Li–C and Be–Si, q = −2 to +4) in 2S+1A1g electronic states with spin multiplicities ranging from the singlet to the septet. With some exceptions, we find that closed-shells or open-shells half-filled with same spin electron systems have large multicentre indices and negative NICS values that are characteristic patterns of aromatic compounds. Our results confirm the existence of octahedral aromaticity but do not allow us to define a general rule for octahedral aromaticity because the ordering of molecular orbitals does not remain the same for different octahedral clustersThis work has been supported by the Ministerio de Economía y Competitividad (MINECO) of Spain (Project CTQ2014-54306-P) and the Generalitat de Catalunya (project 2014SGR931, Xarxa de Referència en Química Teòrica i Computacional, ICREA Academia 2014 prize for M. S., and grant No. 2014FI_B 00429 to O.E.B.). F. F. acknowledges financial support of the Beatriu de Pinós programme from AGAUR for the postdoctoral grants BP_A_00339 and BP_A2_00022. The EU under the FEDER grant UNGI10-4E-801 (European Fund for Regional Development) has also funded this research. J. P. thanks the National Research School Combination – Catalysis (NRSC-C), and The Netherlands Organization for Scientific Research (NWO/CW and NWO/NCF