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The bond-formation processes between the d(10) metal fragments Ni(PR3)(2) (R = H, CH3, F, CF3, Ph) and acetylene have been studied by density functional theory with the BP86 functional and large TZV(2df,2pd) basis sets. The Ni-acetylene bonds have been analyzed in terms of distortion and intrinsic interaction energies within the Dewar-Chatt-Duncanson model of bonding. The intrinsic interaction energies have been corrected for basis set superposition error (BSSE). Linear relationships have been found between the intrinsic interaction energies and the distances of the Ni-C and C&3bond; C bonds as well as with the acetylene-nickel pi-backbonding. No linear relationship with respect to the total interaction energies was found. Despite using large basis sets, BSSE still contaminates the interaction energies by 5-10 %. For the PR3 ligands, the BSSE-corrected intrinsic interaction energies of acetylene bonding increase in the order P(CF3)(3) < PF3 < PPh3 < PH3 < P(CH3)(3) from 58.9 to 77.9 kcal mol(-1), while the total interaction energies range from 32.9 to 42.4 kcal mol(-1) in the order PPh3 < P(CF3)(3) < P(CH3)(3) < PH3 < PF3. These results reveal that the total influence of PH3 and PPh3 on the thermodynamics of the acetylene bonding is different and therefore in this sense PH3 is not a good model of PPh3 in theoretical calculations.