Nonrelativistic and scalar relativistic pseudopotential calculations were carried out for the isoelectronic series of diatomic molecules AuPt-,Au-2, and AuHg+ at the Hartree-Fock, second-order Moller-Plesset (MP2), and coupled-cluster [CCSD(T)] level. For Au-2 we performed large scale fully relativistic Dirac-Hartree-Fock and MP2 benchmark calculations in order to test the reliability of the pseudopotential approximation. Both methods yield almost identical spectroscopic properties for Au-2. The comparison further reveals that pseudopotentials correctly describe the effects of relativity on the spectroscopic properties of Au-2. The yet unknown diatomic species AuPt- and AuHg+ are stable compounds, and their rotational-vibrational constants are predicted. These show striking similarities compared to the values of Au-2. MP2 results including a set of three g-functions per metal atom indicate that higher angular momentum functions are important for accurately predicting the bond distance of these molecules.