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Hydrogen bonds (H‐bonds) have been shown to modulate the chemical reactivities of iron centers in iron‐containing dioxygen‐activating enzymes and model complexes. However, few examples are available that investigate how systematic changes in intramolecular H‐bonds within the secondary coordination sphere influence specific properties of iron intermediates, such as iron‐oxido/hydroxido species. Here, we used 57Fe nuclear resonance vibrational spectroscopy (NRVS) to probe the Fe‐O/OH vibrations in a series of FeIII‐hydroxido and FeIV/III‐oxido complexes with varying H‐bonding networks but having similar trigonal bipyramidal primary coordination spheres. The data show that even subtle changes in the H‐bonds to the Fe‐O/OH units result in significant changes in their vibrational frequencies, thus demonstrating the utility of NRVS in studying the effect of the secondary coordination sphere to the reactivities of iron complexes. Hydrogen bond strength to iron(III)‐oxido/hydroxido (FeIII−O/OH) units in nonheme iron complexes is revealed by 57Fe nuclear resonance vibrational spectroscopy, thus providing a methodology to elucidate the influence of hydrogen bonds in the secondary coordination sphere to the stability of FeIII−O/OH units, and potentially connecting it to the reactivities of FeIV−O units. [ABSTRACT FROM AUTHOR]