The electron transfer (ET) properties of 10- and 12-vertex carboranes are investigated by the ab initio Hartree-Fock method within the Marcus-Hush (MH) two-state model and the Koopman theorem (KT) approach. The calculated value of the ET coupling matrix element, V-AB, is consistently higher in the KT approach than in the MH two-state model. For the carborane molecules functionalized by -CH2 groups at C-vertices, V-AB Strongly depends on the relative orientation of the planes containing the terminal -CH2 groups. The predicted conformation dependence Of V-AB offers a molecular mechanism to control ET between two active centers in molecular systems. (c) 2005 Elsevier B.V. All rights reserved.