Electronic structure studies of diradicals derived from Closo-Carboranes

Abstract

Electronic structure computations have been performed on diradical systems composed of two carborane radicals CB11H12 connected through acetylene, ethylene and ethane bridge units, leading, respectively, to a linear and two trans structures. Each cage possesses one unpaired electron and the total system can thus be coupled to a singlet or a triplet state. Numerical determinations using the spin-projected method with a hybrid B3LYP functional show that these compounds have singlet ground states with low singlet–triplet energy gaps of 0.004 eV (acetylene bridge), 0.080 eV (ethylene bridge) and 0.0005 eV (ethane bridge). Spin population analyses point out a left/right localized spin distribution in the spin-projected wave function. The possibility of mapping these results onto a Heisenberg spin Hamiltonian is considered, in order to predict low-lying excited states in extended carborane chains.