Ab-initio MP2/aug'-cc-pVTZ calculations have been performed to determine the structures and binding energies of proton-bound complexes stabilized by N-H+-P hydrogen bonds and to investigate the nature of the proton-transfer coordinate in these systems. Double minima are found only when the difference between the protonation energies of the N and P bases is less than about 4 kcal/mol. The isomer in which the protonated nitrogen base is the donor lies lower on the potential surface and also has a greater binding energy relative to the corresponding isolated monomers. Equation-of-motion coupled cluster singles and doubles (EOM-CCSD) calculations have been employed to obtain one- and two-bond spin-spin coupling constants across these hydrogen bonds. Two-bond coupling constants (2h)J(N-P) correlate with N-P distances, irrespective of whether the donor ion is N-H+ or P-H+. One-bond coupling constants (1)J(N-H) and (1h)J(H-P) for complexes stabilized by N-H+center dot center dot center dot P hydrogen bonds correlate with corresponding distances, but similar correlations are not found for (1)J(P-H) and (1h)J(H-N) for complexes with P-H+center dot center dot center dot N hydrogen bonds. Negative values of K-1h(H-N) and K-1h(H-P) indicate that the hydrogen bonds in these complexes are traditional. Comparisons are made with complexes stabilized by N-H+-N and P-H+-P hydrogen bonds.