Using bis(β-diketiminate) ligands we were able to synthesize unprecedented indium and thallium biscarbenoids. For indium, a novel four-membered metallacycle is derived from intra- and intermolecular In-In interactions in the solid state, while for thallium only an intramolecular Tl2-pseudo-dimer is obtained. Computational studies revealed that the solid-state structures benefit significantly from dispersion stabilization.