## Abstract

Qualitative molecular orbital (MO) theory predicts that square-planar tetrasilacyclobutanetetraone D_{4h}-(SiO)_{4} should, like D_{4h}-(CO)_{4}, have a triplet ground state, and the results of the (U)CCSD(T)-F12b/cc-pVTZ-F12//(U)B3LYP/6-311+G(2df) calculations, reported here, confirm this expectation. Calculations at the same level of theory find that square-planar tetrasilacyclobutanetetrathione D_{4h}-(SiS) _{4} also has a triplet ground state. However, these ab initio calculations predict that (SiO)_{4} and (SiS)_{4} both have a singlet state of much lower energy, with a tetrahedral (T_{d}) equilibrium geometry and six, electron-deficient, Si-Si bonds. In contrast, the lowest singlet state of (CO)_{4} and of (CS)_{4} is calculated to prefer a D_{4h} to a T_{d} geometry. An analysis, based on the second-order Jahn-Teller effect, rationalizes the influence of the electronegativity difference between A and Y in (AY)_{4} on the energy difference between a D_{4h} and T_{d} geometry. This analysis predicts that (BF)_{4} and (BCl)_{4}, which are isoelectronic with, respectively, (CO)_{4} and (CS)_{4}, should both prefer a T_{d} to a D_{4h} equilibrium geometry. These qualitative predictions have been confirmed by our calculations, and (BCl)_{4} is known experimentally to have a T_{d} equilibrium geometry.

Original language | English |
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Pages (from-to) | 19282-19291 |

Number of pages | 10 |

Journal | Journal of the American Chemical Society |

Volume | 135 |

Issue number | 51 |

DOIs | |

State | Published - 26 Dec 2013 |

Externally published | Yes |