σ-Aromaticity Planar Pentacoordinate Beryllium Atoms.

Area of Science:

• Computational Chemistry
• Inorganic Chemistry
• Materials Science

Background:

• Hypercoordinate compounds challenge traditional bonding theories.
• Planar pentacoordinate structures are rare, especially with s-block elements.
• Beryllium's electronic configuration typically limits its coordination number.

Purpose of the Study:

• To explore the possibility of six-valence-electron planar pentacoordinate beryllium (ppBe) as a global minimum.
• To investigate the bonding characteristics and stability of BeM5+ (M = Cu, Ag, Au) complexes.
• To understand the role of σ aromaticity in stabilizing these novel structures.

Main Methods:

• Density Functional Theory (DFT) calculations were employed.
• Electronic structure and bonding analyses were performed.
• Vibrational frequency calculations confirmed stability.

Main Results:

• Six-valence-electron planar pentacoordinate beryllium (ppBe) was identified as a stable global minimum in BeM5+ (M = Cu, Ag, Au).
• The bonding involves excited-state beryllium with a 2p^1 2p^1 configuration, featuring σ donations and back-donations.
• Three delocalized σ orbitals contribute to σ aromaticity, stabilizing the high D5-symmetry ppBe.

Conclusions:

• The study demonstrates the feasibility of s-block metals forming stable planar pentacoordinate beryllium complexes.
• σ Aromaticity is the key factor for the stability of these hypercoordinate compounds.
• This work expands the understanding of hypercoordinate bonding in s-block elements.