B18Ta4-Zhang Yu-acsomega.1c00828

      Cage-like metallo-borospherenes exhibit unique structures and bonding. Inspired by the newly reported smallest spherical trihedral metallo-borospherene D3h Ta3B12− (1), which contains two equivalent B3 triangles interconnected by three B2 units on the cage surface, we present herein a first-principles theory prediction of the perfect spherical tetrahedral metallo-borospherene Td Ta4B18 (2), which possesses four equivalent B3 triangles interconnected by six B atoms, with four equivalent nonacoordinate Ta centers in four η9 -B9 rings as integrated parts of the cage surface. As the well-defined global minimum of the neutral, Ta4B18 (2) possesses four 10c-2e B9(π)−Ta(dσ) and eight 10c-2e B9(π)− Ta(dδ) coordination bonds evenly distributed over four Tacentered Ta@B9 nonagons, with the remaining 18 valence electrons in nine 22c-2e totally delocalized bonds following the 18-electron principle (1S2 1P6 1D10) of a superatom. Such a bonding pattern renders spherical aromaticity to the tetrahedral complex, which can be used as building blocks to form the face-centered cubic crystal Ta4B15 (3). The IR, Raman, and UV−vis spectra of Ta4B18 (2) are theoretically simulated to facilitate its future experimental characterizations.