Two-dimensional lattice oligomers of diboraspiropentadiene: a quantum chemical study

According to B3LYP/6-311G(d,p) density functional calculations, the most energetically favorable method of assembling diboraspiropentadiene molecules into dimers, trimers, tetramers, and higher two-dimensional (2D) oligomers is to join the diboraspiropentadiene units with the formation of C-B bonds and the diboraspiropentadiene units trans-arranged relative to these bonds. Using this procedure, stable 2D lattice structures comprising 4, 7, 9, 16, or 25 monomer units were constructed in such a manner that each unit retains a nonclassical planar configuration of four bonds formed by the central carbon atom. Enlargement of the planar oligomers results in narrowing of the HOMO-LUMO gap and a considerable increase in the dipole moment. High negative NICS values suggest that the three-membered rings retain their aromaticity, whereas the ten-membered rings formed involving different monomer units in constructing oligomeric structures are strongly antiaromatic.