Sandwich complexes of the P42- aromatic ring with the first row transition metal

The equilibrium geometries, energies, harmonic vibrational frequencies, and nucleus-independent chemical shifts (NICS) of the new type sandwich structures [P4MP4]n− (M = Ti, V, Cr, Mn, Fe, Co, and Ni; n = 0, 1 or 2) are researched at the B3LYP/6-311G∗ and B3PW91/6-311G∗ levels of theory. The calculations reveal that the Ti, V, Cr, and Mn species adopt the eclipsed (D4h) conformations, while the Fe, Co, and Ni analogs adopt the staggered (D4d) conformations as their stable structures, and once the sandwich complexes are formed, the P42- square properties remain unchanged. The NICS calculations confirm that the P42- ring in the Ti, V, Cr, and Mn species exhibit σ and π antiaromaticity, while it exhibit σ and π aromaticity in the Fe, Co, and Ni analogs.