applying an OEEF of -1 VÅ -1 along the Fe-N2 vector induces a dipole moment of only 0.75D, corresponding to < 2 kcal/mol energetic stabilization (Figure ). A small dipole moment may result from electron transfer to, or from, the FeMo cluster upon coordination. However, due to the large HOMO-LUMO gap of isolated N2, this is presumably a very minor effect: Head-Gordon and co-workers reported a transfer of a mere 0.03 e -from N2 to the catalytic cluster in their advanced electronic structure calculations. The emergence of a minuscule positive charge on N2 upon coordination would lead to an induced dipole that is stabilized by a negative Fz pointing towards Fe2. As such, as an isolated event, when all other factors are equal, binding of N2 to Fe2 ought to be favored over binding to Fe6. However, the stabilization that could be achieved through interaction of this extremely small dipole with the electrostatic environment around Fe2 will most likely be negligible for most nitrogenases. Indeed, simulations by Head-Gordon et al. have revealed that N2 coordination to Fe2 forces a 90° rotation of the imidazole of His195 to minimize steric clash. This leads to a significant reduction of the OLEF around Fe2 (left-hand side of Figure ). A coordinated H2S molecule, or a hydrosulfide group, on the Fe2 site on the other hand does not require rotation of His195 (right-hand side of Figure ). What's more, this species is highly susceptible an external electric field: an OEEF of -1 VÅ -1 aligned with the dipole moment of the H2S causes µ to rise to 2.2D. The corresponding energetic stabilization is >8 kcal/mol (cf. Figure ).