Realization of an Al≡Al Triple Bond in the Gas-Phase Na₃ Al₂ ^- Cluster via Double Electronic Transmutation

The discovery of homodinuclear multiple bonds composed of Group 13 elements represents one of the most challenging frontiers in modern chemistry. A classical triple bond such as N≡N and HC≡CH contains one σ bond and two π bonds constructed from the p orbitals perpendicular to the σ bond. However, the traditional textbook triple bond between two Al atoms has remained elusive. Here we report an Al≡Al triple bond in the designer Na₃ Al₂ ^- cluster predicted in silico, which was subsequently generated by pulsed arc discharge followed by mass spectrometry and photoelectron spectroscopy characterizations. Being effectively Al^2- due to the electron donation from Na, the Al atoms in Na₃ Al₂ ^- undergo a double electronic transmutation into Group 15 elements, thus the Al^2- ≡Al^2- kernel mimics the P≡P and N≡N molecules. We anticipate this work will stimulate more endeavors in discovering materials using Al^2- ≡Al^2- as a building block in the gas phase and in the solid state.