Complex with Linear B-B-B Skeleton Trapped in Dinitrogen Matrix: Matrix Infrared Spectra and Quantum Chemical Calculations.

The neutral (NN)-B-B-B-(N) complex has been trapped in low-temperature dinitrogen matrix and identified by isotopic substitution and theoretical frequency calculations. The linear B-B-B skeleton is stabilized by two inequivalent N, namely, one end-on and other side-on N. The structure of linear B-B-B skeleton illustrates much difference from previously reported triangle configuration of B clusters. Frontier orbital analysis demonstrates that the σ orbital of end-on NN and the π-bonding orbital of side-on N acts as the donor orbital. π bonding character across B-B-B skeleton donates to the antibonding π* orbital of end-on NN and out of phase the B-B-B features π back-donation to antibonding π* orbital of side-on N. The combination of strong σ-donating capacity coupled with a greater ability for accepting π-back-donation of the N ligand leads to the formation of (NN)-B-B-B-(N) complex with linear B-B-B skeleton. In addition, complexes of (NN)B(NN), (NN)BB(NN), and (NN)B(NN) have been identified in our experiments.