Molecules of the type NgMX (Ng = Xe, Rn; M - Cu-Au; X = F, Cl) were studied at correlated levels of theory with extended polarized basis sets. Atomic charges, populations, and orbitals were calculated with the natural population analysis method. The calculated values for the xenon compounds agree very well with experimental data. Trends going from xenon to radon are discussed. The bonding in the radon compounds is found to be very similar to that in the xenon compounds. A small increase in bond lengths and interaction energies are consistent with the expected periodic trends in the noble gases. (C) 2015 Elsevier B.V. All rights reserved.