Hf<sub>3</sub> Cluster Is Triply (σ-, π-, and δ-) Aromatic in the Lowest <i>D</i><sub>3</sub><i><sub>h</sub></i>, <sup>1</sup>A<sub>1</sub>‘ State

2007-12-20T00:00:00Z (GMT) by Boris B. Averkiev Alexander I. Boldyrev
The extensive search for the global minimum structure of Hf<sub>3</sub> at the B3LYP/LANL2DZ level of theory revealed that <i>D</i><sub>3</sub><i><sub>h</sub></i> <sup>3</sup>A<sub>2</sub>‘ (1a<sub>1</sub>‘<sup>2</sup>1a<sub>2</sub>‘ ‘<sup>2</sup>1e‘<sup>4</sup>2a<sub>1</sub>‘<sup>2</sup>1e‘ ‘<sup>2</sup>) and <i>D</i><sub>3</sub><i><sub>h</sub></i> <sup>1</sup>A<sub>1</sub>‘ (1a<sub>1</sub>‘<sup>2</sup>2a<sub>1</sub>‘<sup>2</sup>1e‘<sup>4</sup>1a<sub>2</sub>‘ ‘<sup>2</sup>3a<sub>1</sub>‘<sup>2</sup>) are the lowest triplet and singlet states, respectively, with the triplet state being the lowest one. However, at the CASSCF(10,14)/Stuttgart+2f1g level of theory these two states are degenerate, indicating that at the higher level of theory the singlet state could be in fact the global minimum structure. The triplet <i>D</i><sub>3</sub><i><sub>h</sub></i> <sup>3</sup>A<sub>2</sub>‘ (1a<sub>1</sub>‘<sup>2</sup>1a<sub>2</sub>‘ ‘<sup>2</sup>1e‘<sup>4</sup>2a<sub>1</sub>‘<sup>2</sup>1e‘ ‘<sup>2</sup>) structure is doubly (σ- and π-) aromatic and the singlet <i>D</i><sub>3</sub><i><sub>h</sub></i> <sup>1</sup>A<sub>1</sub>‘ (1a<sub>1</sub>‘<sup>2</sup>2a<sub>1</sub>‘<sup>2</sup>1e‘<sup>4</sup>1a<sub>2</sub>‘ ‘<sup>2</sup>3a<sub>1</sub>‘<sup>2</sup>) structure is the first reported triply (σ-, π-, and δ-) aromatic system.