A systematic ab initio investigation has been carried out to determine the structures, binding energies, and spin-spin coupling constants of ternary complexes X:HBO:Z for X, Z =LiH, HNC, HF, HCN, HCl, CIF, and HBO. All complexes X:HBO:Z are linear with C-infinity nu, symmetry, except for HC1:HBO:Z and CIF:HBO:Z which have C, symmetry, thereby reflecting the structures of the corresponding X:HBO and HBO:Z complexes. Cooperative effects on energies are synergistic in all ternary complexes. The enhanced binding energies of complexes X:HBO:Z correlate with the binding energies of the X:HBO and I1130:Z complexes. Coupling constants (1)J(B-H) and (2h)J(B-A) across B-H A hydrogen bonds correlate with the B-A distance, and exhibit synergistic effects due to the presence of Z. (1h)J(H-A) indicates that these bonds have little proton-shared character. Coupling constants across D-(HO)-O-... hydrogen bonds, H-Li O lithium bonds, and F-Cl-... O halogen bonds are also sensitive to the synergistic effects arising from the presence of X. D-H...O hydrogen bonds in ternary complexes are traditional (normal) hydrogen bonds.