Probing P-H+-P hydrogen bonds: structures, binding energies, and spin-spin coupling constants

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Physical Chemistry

Background:

• Phosphorus compounds are versatile building blocks in chemistry.
• Understanding hydrogen bonding in phosphorus systems is crucial for predicting reactivity and properties.
• Proton transfer dynamics in phosphorus-based hydrogen bonds remain an active area of research.

Purpose of the Study:

• To investigate the structures and binding energies of complexes formed between phosphorus bases and their protonated ions.
• To elucidate the nature of P-H+-P hydrogen bonds using advanced computational methods.
• To explore the relationship between spectroscopic coupling constants and the geometry of these complexes.

Main Methods:

• Ab initio MP2/aug'-cc-pVTZ calculations were employed to determine equilibrium structures and binding energies.
• EOM-CCSD calculations were used to compute (31)P-(31)P and (31)P-(1)H coupling constants.
• Analysis of potential energy surfaces and reduced coupling constants provided insights into hydrogen bond character.

Main Results:

• Twenty-two open and three cyclic complexes were characterized, with most exhibiting linear P-H+-P hydrogen bonds.
• Isomers with the conjugate acid of the weaker base as the proton donor showed increased proton-shared character and larger binding energies.
• Positive values of (2h)K(P-P) and (1)K(P-H), and negative values of (1h)K(H-P) confirmed traditional hydrogen bonding.
• (2h)J(P-P) values effectively distinguish between open and cyclic complexes, correlating with P-P distances.

Conclusions:

• The study provides a detailed computational analysis of phosphorus-containing hydrogen-bonded complexes.
• Spectroscopic parameters, particularly (2h)J(P-P), can serve as experimental probes to differentiate complex geometries.
• These findings contribute to a deeper understanding of non-covalent interactions involving phosphorus.