The binding energies in CuPH3, AgPH3, and AuPH3 complexes, as determined from one-component (scalar) CCSD(T) calculations with aug-cc-pVTZ basis set, are 32.9, 11.5, and 66.7 kJ/mol, respectively. The large binding energy in AuPH3 is essentially due to relativistic effects. On neglecting them the interaction between Au and the lone-electron pair of PH3 results in a weak van der Waals complex. The bonding in M center dot center dot center dot PH3 complexes is interpreted in terms of the charge transfer from the electron lone-pair of PH3 to the metal atom. In AuPH3 this mechanism is supported by the large relativistic increase of the Au electron affinity. (C) 2009 Elsevier B.V. All rights reserved.