where k ET (0) and k ET (x) are the k ET values at the electrode surface (x = 0) and at the distance x from it, respectively, and β is the tunneling decay coefficient. Studies of electron tunneling using redox centers tethered to organic molecules with typical lengths of 5-50 Å on metal electrodes revealed β values of 1.0-1.2 Å -1 for alkanethiol chains, 0.4-0.6 Å -1 for π-conjugated chains, and 0.2-0.3 Å -1 for aromatic chains. Tunneling through vacuum between two metals typically yields β values of 2.0-2.5 Å -1 . Consequently, one could be tempted to perform a linear fit of data in Fig. by adopting Eq. ( ) for k 0 . Doing so would yield β of 0.4-0.5 Å -1 , which is somewhat smaller than expected for a wide bandgap insulator. In fact, it is evident from Fig. that the distance dependence of ln(k 0 ) is not linear and decays more slowly as x increases, as seen for ≥ 3L hBN. When only 1L and 2L hBN are considered for the linear fit, reasonable β values of 1.2 Å -1 and 1.1 Å -1 for [IrCl 6 ] 3- and [Ru(NH 3 ) 6 ] 3+ are obtained. The deviation from Eq. (1) at large x becomes very apparent when the data are normalized to k 0, gra , as shown in Figs. and. Plotted this way, the linear fit ought to pass near the origin, since, by definition, for x = 0 the argument of the natural logarithm is 1.