Carbon-Carbon to Boron-Nitrogen isosterism enables to switch toward fused 3D/2D magnetically aromatic systems

Abstract

The realization of genuine 3D/2D aromatic systems through fusion of BN/CC isosteric azaborines with carborane clusters has been systematically examined using magnetic response analysis. Current density maps, bond current strengths, and DIAL surfaces demonstrate that magnetic descriptors provide the most sensitive criterion for multidimensional aromaticity. Although all isolated azaborines are aromatic, the magnitude and uniformity of their diatropic ring currents strongly depend on the number and relative positioning of BN units, with consecutive BN incorporation attenuating and polarizing the circulation. Fusion studies reveal that neither benzene nor mono-BN azaborine sustains integrated 3D/2D aromaticity due to a strong paratropic current localized at the fusion bond. In contrast, systems containing two consecutive BN/CC isosteres-particularly 1,4-diaza-2,3diborine and 1,4-diaza-2-borine-exhibit a continuous diatropic ring current across the interface, consistent with effective magnetic communication between the planar ring and the boron cage. Electronic and energetic analyses support these findings but are less discriminating than magnetic criteria. Overall, this work establishes magnetic response properties as decisive tools for identifying viable 3D/2D aromatic systems and defines structural requirements for their design.