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&#8722;X&#8901;&#8901;&#8901;O=PMe₃ halogen bond energy &#916;<i>E</i>, X&#8901;&#8901;&#8901;O distance <i>r</i>, halogen&#8217;s &#963;-hole size, QTAIM parameters at halogen bond critical point and changes of spectroscopic parameters of phosphine oxide upon complexation, such as ³¹P NMR chemical shift, &#916;<i>&#948;</i>P, and P=O stretching frequency, &#916;&#957;. Some of the correlations are halogen-specific, i.e., different for F, Cl, Br, I and At, such as &#916;<i>E</i>(<i>r</i>), while others are general, i.e., fulfilled for the whole set of complexes at once, such as &#916;<i>E</i>(&#916;<i>&#948;</i>P). The proposed correlations could be used to estimate the halogen bond properties in disordered media (liquids, solutions, polymers, glasses) from the corresponding NMR and IR spectra.

Abstract licence: CC BY

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