Ab initio MP2/aug'-cc-pVTZ calculations have been performed to determine the structures and binding energies of complexes formed from five singlet carbene bases acting as electron-pair donors to four ClX acids. Complexes with ClCCH and ClCN are stabilized by traditional halogen bonds. With one exception, complexes with ClNC and ClF are stabilized by (carbene-Cl)(+) center dot center dot center dot -NC and (carbene-Cl)(+) center dot center dot center dot F- ion-pair halogen bonds subsequent to chlorine transfer. These complexes have been characterized in terms of their structures, binding energies, charge-transfer energies, bonding properties, and spin-spin coupling constants. (C) 2017 Elsevier B.V. All rights reserved.