Dr. Toms Rekis (@molcrystalguy.bsky.social)

Recently, we studied hexaurea iron(iii) nitrate. The structure turned out to be incommensurately modulated featuring not only a displacive but also an occupational modulation. What we still don’t understand is why the crystals are blue/bluish. The paper is here: pubs.acs.org/doi/10.1021/...

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Incommensurate Displacive and Occupational Modulation in Hexakis(Urea-O)Iron(III) Nitrate The structure of hexakis(urea-O)iron(III) nitrate is found to be incommensurately modulated. It is described in (3 + 1)-dimensional superspace adopting the superspace group C2/c(σ10σ3)00 with the modulation wavevector q = −0.7394(7)a∗+0.9390(8)c∗. Up to the third-order satellite reflections are observed in the diffraction data collected at 100 K. Consequently, there is an anharmonic displacive modulation present in the hexacoordinated iron(III) complex. Nitrate ions are found in two symmetrically independent sites in the unit cell and form two disordered ensembles with three disordered components and two disordered components, respectively. The latter site is located near a 2-fold axis, resulting in a total of four disorder components for this molecular site. Along with the displacive modulation for the nitrate ions, there is also a complex occupational modulation present. Possible origins of the modulation are discussed. https://pubs.acs.org/doi/10.1021/acs.cgd.4c01457#