The ground electronic state of the eka-mercury dimer (E112₂) was studied within the model of generalized relativistic effective core potentials. A combined procedure based on describing correlation effects by the scalar relativistic coupled-cluster method and on taking into account spin-dependent interactions by means of density-functional theory was used in the calculations. A high accuracy of this approach was confirmed by the results of similar calculations for the mercury dimer. It was found that the bond length is nearly 0.4 Å shorter in E112₂ than in Hg₂ and that the dissociation energy of the former is approximately twice as high as that of the latter dimer.