Ab initio MP2/aug'-cc-pVTZ calculations have been carried out to determine the structures and binding energies of homodimers (PHFX)(2) for X = F, Cl, CN, CH3, and NC. Geometric isomers of these complexes with C, symmetry exist, which are differentiated in terms of the nature of the atoms (F-P center dot center dot center dot P-F, H-P center dot center dot center dot P-H, or A-P center dot center dot center dot P-A, with A being the atom of X directly bonded to P), which approach a nearly linear alignment. Of these, isomers having F-P center dot center dot center dot P-F linear are the most stable. Binding energies, intermolecular distances, and EOM-CCSD spin-spin coupling constants are sensitive to both the nature of X and the atoms that assume the linear alignment.