Realization of an Al≡Al Triple Bond in the Gas-Phase Na Al 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 Na Al cluster predicted in silico, which was subsequently generated by pulsed arc discharge followed by mass spectrometry and photoelectron spectroscopy characterizations. Being effectively Al due to the electron donation from Na, the Al atoms in Na Al undergo a double electronic transmutation into Group 15 elements, thus the Al ≡Al kernel mimics the P≡P and N≡N molecules. We anticipate this work will stimulate more endeavors in discovering materials using Al ≡Al as a building block in the gas phase and in the solid state.