The structures and bonding of the CE42 clusters (E = Al, Ga, In, Tl) have been theoretically studied via B3LYP/def2-TZVP computations. Total energies were recalculated at the CCSD(T)/def2-TZVPP//B3LYP/def2-TZVP level in order to corroborate the energy differences. Our computations show that all the CE42 and CE4Li clusters (E = Al, Ga, In, Tl) have a planar tetracoordinate carbon structure. Interestingly, while the most stable form of CAl4Li and CGa4Li is planar with coordination of Li+ to an edge of the CE42 fragment, for CIn4Li and CTl4Li the pyramidal structures with C-4v symmetry are the lowest-energy structures. (C) 2011 Elsevier B.V. All rights reserved.