Bifurcated Dihydrogen Bonding in the Uptake of Gas-Phase Diborane on Silica

The interfacial chemistry of diborane (B2H6) with hydroxylated silica was investigated via in situ Fourier-transform infrared spectroscopy and temperature-programmed desorption. During exposure of silica to B2H6 under ultrahigh vacuum conditions, a decline in infrared band intensity assigned to excitation of the interfacial silanol O–H vibration at 3750 cm–1 and the associated appearance of a feature at 3687 cm–1 revealed hydrogen-bonding interactions between B2H6 and interfacial silanol groups. The IR spectrum for silica was completely recovered following desorption of the adsorbates, indicating that interactions between B2H6 and clean silica are reversible, in contrast to other reports on this system. During temperature-programmed desorption of diborane from silica, B2H6 was observed to desorb between 80 and 150 K, evidence for weak interactions between B2H6 and the surface. Electronic-structure calculations revealed that these interactions were due to bifurcated dihydrogen bonds between two terminal B–H groups of the adsorbate and interfacial silanol groups.