Observation of Double-Ring Tubular B20(CO)n+ (n = 1–8)：Emergence of 2D-to-3D Transition in Boron Carbonyl Complexes

Abstract

The consecutive discoveries of double-ring (DR) tubular D10d B20 and D2d B20+ as embryos of single-walled boron nanotubes have attracted considerable attention in the past two decades. Joint chemisorption experiment and first-principles theory investigations performed herein indicate that, as the only isomer of the monocation observed in gas-phase experiments, DR tubular D2d B20+ can react with CO successively under ambient conditions to form a series of DR tubular boron carbonyl monocations B20(CO)n+ up to n = 8, presenting the largest boron carbonyl complexes observed to date which mark the 2D-to-3D transition in boron carbonyl complexes. DR tubular D2d B20+ with twenty periphary boron atoms is found to be about ten times more reactive to chemisorb the first CO than the experimentally known quasi-planar C2v B13+ (B3@B10+) with typical π-aromaticity, but about ten times less reactive than both quasi-planar Cs B11+ (B2@B9+) and C2v B15+ (B4@B11+) with σ and π conflicting aromaticity. Extensive theoretical calculations and analyses unveil the chemisorption pathways, potential energy profiles, and chemical bonding patterns of the DR tubular B20(CO)n+ and their neutral counterparts B20(CO)n which both appear to be tubularly aromatic in nature.