Hydrogen Bonding of OOH Group in Crystalline Adducts of Organic Hydroperoxides with Cage Tertiary Amines, Their N-Oxides, and a Phosphine Oxide: A Combined X-ray Crystallography and DFT Study

Cocrystallization with appropriate organic molecules has been known as an effective and practical strategy for stabilization of organic hydroperoxides─useful oxidants, free-radical polymerization initiators, and emerging pharmaceuticals. In this paper, two peroxosolvates (H₂O₂·HMTA (1), 0.843H₂O₂·0.157H₂O·DABCO N-oxide (2)) and 11 adducts of organic hydroperoxides (2^tBuOOH·DABCO (3), 2CmOOH·DABCO (4), 2^tBuOOH·HMTA (5), 3^tBuOOH·DABCO N-oxide (6), CmOOH·Ph₃PO (7), Cy(OOH)₂·DABCO N-oxide (8), Cy(OOH)₂·DABCO N-oxide·0.5C₆H₆ (9), [Cy(OOH)O]₂·HMTA N-oxide (10), [Cy(OOH)O]₂·DABCO N-oxide (11), [Cy(OOH)O]₂·2DABCO N-oxide·2CHCl₃ (12), [Cy(OOH)O]₂·Ph₃PO (13)) were structurally characterized for the first time, providing the relationships with the nature of components. The energetic superiority of O–H···O^––N⁺ and O–H···O═P over O–H···N hydrogen bonds (E_HB = 30.5–69.3 kJ mol^–1) was against the lower basicity of amine N-oxides and Ph₃PO over amine coformers. This was computationally attributed to the nearly 3-fold increase of partial atomic charges in the former hydrogen bond acceptors, in light of the interaction electrostatic nature. Nine compounds were synthesized according to the proposed facile approach and investigated by FTIR and Raman spectroscopy, thermal analysis, and powder XRD. Thermal stability of the cocrystals was found to be improved by the utilization of heavy coformers and less volatile hydroperoxides, rather than being correlated with hydrogen bond energy.