Like (CO)4, Do (CS)4 and (CSe)4 have a triplet ground state?

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Molecular Spectroscopy

Background:

• The ground state electronic configuration of small ring molecules is crucial for understanding their reactivity and properties.
• Cyclobutane-1,2,3,4-tetraone ((CO)4) exhibits a triplet ground state, a unique characteristic among similar cyclic compounds.

Purpose of the Study:

• To computationally investigate the ground state electronic configurations of cyclobutane-1,2,3,4-tetrathione ((CS)4) and cyclobutane-1,2,3,4-tetraselenone ((CSe)4).
• To elucidate the factors contributing to the difference in ground states between (CO)4, (CS)4, and (CSe)4.

Main Methods:

• Utilized (U)CCSD(T) computational calculations to determine the electronic structure.
• Analyzed molecular orbital (MO) occupations and coefficients, specifically focusing on b2g σ and a2u π MOs.

Main Results:

• Both (CS)4 and (CSe)4 were predicted to have singlet ground states, with the b2g σ MO doubly occupied and the a2u π MO empty.
• Longer carbon-chalcogen bond distances and reduced coefficients on carbon atoms in the b2g and a2u MOs were identified as key factors for the singlet ground states in (CS)4 and (CSe)4 compared to (CO)4.

Conclusions:

• The electronic structure of cyclic tetra-chalcogenones significantly differs from tetra-ketones.
• An experimental verification for the predicted singlet ground state of (CS)4 is proposed to validate these computational findings.