Phosphine Oxides as Spectroscopic Halogen Bond Descriptors: IR and NMR Correlations with Interatomic Distances and Complexation Energy.

An extensive series of 128 halogen-bonded complexes formed by trimethylphosphine oxide and various F-, Cl-, Br-, I- and At-containing molecules, ranging in energy from 0 to 124 kJ/mol, is studied by DFT calculations in vacuum. The results reveal correlations between R-X⋅⋅⋅O=PMe halogen bond energy Δ, X⋅⋅⋅O distance , halogen's σ-hole size, QTAIM parameters at halogen bond critical point and changes of spectroscopic parameters of phosphine oxide upon complexation, such as P NMR chemical shift, ΔP, and P=O stretching frequency, Δν. Some of the correlations are halogen-specific, i.

Conformational Mobility and Proton Transfer in Hydrogen-Bonded Dimers and Trimers of Phosphinic and Phosphoric Acids.

The monomers, H-bonded cyclic dimers, and trimers of five acids were studied by density functional theory calculations, such as hypophosphorous acid (HPOOH, ), dimethylphosphinic acid (MePOOH, ), phenylphosphinic acid (PhHPOOH, ), dimethylphosphoric acid ((MeO)POOH, ), and diphenylphosphoric acid ((PhO)POOH, ). Particular attention was paid to the conformational manifold existing due to the internal degrees of freedom: proton transfer (PT), puckering ("twist") within the ring of H-bonds, and mobility of the substituents (namely, -Ph, -OMe, and -OPh rotations). For acid , the number of conformers is additionally increased because of the varying relative orientation of nonequivalent substituents in cyclic complexes.