A high-pressure iron K-edge x-ray absorption spectral study of the spin-state crossover in (Fe[HC(3,5-(CH(3))(2)pz)(3)](2))I(2) and (Fe[HC(3,5-(CH(3))(2)pz)(3)](2))(BF(4))(2).

The room temperature iron K-edge X-ray absorption near edge structure spectra of (FeHC(3,5-(CH(3))(2)pz)(3))I(2) and (FeHC(3,5-(CH(3))(2)pz)(3))(BF(4))(2) have been measured between ambient and 88 and 94 kbar, respectively, in an opposed diamond anvil cell. The iron(II) in (FeHC(3,5-(CH(3))(2)pz)(3))I(2)undergoes the expected gradual spin-state crossover from the high-spin state to the low-spin state with increasing pressure. In contrast, the iron(II) in (FeHC(3,5-(CH(3))(2)pz)(3))(BF(4))(2) remains high-spin between ambient and 78 kbar and is only transformed to the low-spin state at an applied pressure of between 78 and 94 kbar. No visible change is observed in the preedge peak in the spectra of (FeHC(3,5-(CH(3))(2)pz)(3))I(2) with increasing pressure, whereas the preedge peak in the spectra of ((eHC(3,5-(CH(3))(2)pz)(3))(BF(4))(2) changes as expected for a high-spin to low-spin crossover with increasing pressure. The difference in the spin-state crossover behavior of these two complexes is likely related to the unusual behavior of (FeHC(3,5-(CH(3))(2)pz)(3))(BF(4))(2) upon cooling.