Fig. 4. (Left) VT-UV/vis spectroscopy in DCM ranging from 20 to –80 °C. The absorbance maximum at 470 nm is attributed to the apical isomer (2) while the maxima at 385 and 561 nm are attributed to the equatorial isomer (1). (Right) Predicted FTIR spectrum from DFT calculation. Experimental data at 20 °C is shown as the black trace, apical isomer shown as the red trace, equatorial isomer shown as green trace, and TBP isomer as blue trace.