College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou, Jiangsu, P R China.
Chemistry. 2013 Apr 26;19(18):5687-93. doi: 10.1002/chem.201204049. Epub 2013 Mar 1.
Cyclobutane-1,2,3,4-tetraone, (CO)4, was computationally predicted and, subsequently, experimentally confirmed to have a triplet ground state, in which a b2g σ MO and an a2u π MO were each singly occupied. In contrast, the (U)CCSD(T) calculations reported herein found that cyclobutane-1,2,3,4-tetrathione, (CS)4, and cyclobutane-1,2,3,4-tetraselenone, (CSe)4, both had singlet ground states, in which the b2g σ MO was doubly occupied and the a2u π MO was empty. Our calculations showed that both the longer C=X distances and smaller coefficients on the carbon atoms in the b2g and a2u MOs of (CS)4 and (CSe)4 contributed to the difference between the ground states of these two molecules and the ground state of (CO)4. An experimental test of the prediction of a singlet ground state for (CS)4 is proposed.
环丁烷-1,2,3,4-四酮（CO）4，经计算预测并随后实验证实具有三重态基态，其中 b2gσ MO 和 a2uπ MO 分别被单占据。相比之下，本文报道的 UCCSD(T)计算发现，环丁烷-1,2,3,4-四硫醇（CS）4 和环丁烷-1,2,3,4-四硒酮（CSe）4 均具有单重态基态，其中 b2gσ MO 被双占据，a2uπ MO 为空。我们的计算表明，（CS）4 和（CSe）4 中 b2g 和 a2u MO 上的 C=X 距离较长且碳原子上的系数较小，这两个分子的基态与（CO）4 的基态之间的差异。提出了对（CS）4 单重态基态预测的实验检验。
