Structures of a Complex Hydrazinium Lead Iodide, (N2 H5 )15 Pb3 I21 , Possessing [Pb2 I9 ]5- , [PbI6 ]4- , and I- Ions and α- and ß-(N2 H5 )PbI3.

Photovoltaic perovskites, most notably methylammonium lead triiodide, (NH3 Me)PbI3 , have recently attracted considerable attention, and based upon the modified "Goldschmidt" as well as a "revised" tolerance factors, hydrazinium should be able to occupy the same cation site as methylammonium, and form a cubic unit cell. The reaction of N2 H5+ I- with PbI2 in dimethylformamide results in three types of yellow crystals; hexagonal, needle-like, and rod-like, the structures of which were determined at 100 K. The hexagonal (P63 /m: a=10.8906(10) Å; b=37.845(5) Å) crystals possess isolated face-sharing octahedral [Pb2 I9 ]5- , [PbI6 ]4- , and I- ions. IR spectroscopy indicates the presence of hydrogen-bonded N2 H5+ and the composition was determined by single-crystal X-ray diffraction, density measurements, combustion elemental analysis, and thermogravimetric analysis to be (N2 H5 )15 Pb3 I21 , which is photoluminescent at 50 K, but not at room temperature. The needle and rod crystals have an orthorhombic (Pnma: a=11.1385(7) Å; b=4.4806(3) Å; c=17.6241(11) Å) and hexagonal (P63 /mmc: a=8.7386(9) Å; b=8.2006(9) Å) unit cells, respectively, possessing the perovskite ABX3 composition of (N2 H5 )PbI3 , but neither exhibits the cubic Perovskite structure type. The structures of α- and ß-(N2 H5 )PbI3 possess parallel ribbons of Pb2 I4 and chains of PbI2 , respectively. Strong inter-hydrazinium hydrogen bonding due to it possessing both hydrogen bonding donor and acceptor sites (unlike NH3 Me+ ) appear to stabilize the observed extended ribbon motif for (N2 H5 )15 Pb3 I21 and α-(N2 H5 )PbI3 . (N2 H5 )15 Pb3 I21 has a band-gap-like absorption of 2.34 eV, and both α- and ß-(N2 H5 )PbI3 have a 2.70 eV band-gap-like absorptions.

FlgM proteins from different bacteria exhibit different structural characteristics.

Intrinsically disordered proteins (IDPs) are a unique class of proteins that do not require a stable structure for function. The importance of IDPs in many biological processes has been established but there remain unanswered questions about their evolution and conservation of their disordered state within a protein family. Our group has been studying the structural similarities among orthologous FlgM proteins, a model class of IDPs. We have previously shown that the FlgM protein from the thermophile Aquifex aeolicus has more structure at A. aeolicus' physiological temperature (85°C) than is observed for the Salmonella typhimurium FlgM, suggesting that the disordered nature of FlgM varies among organisms and is not universally conserved. In this work, we extend these studies to the FlgM proteins from Escherichia coli, Pseudomonas aeruginosa, Proteus mirabilis, and Bacillus subtilis. We demonstrate that the B. subtilis, E. coli, and S. typhimurium FlgMs exist in a premolten globule-like conformation, though the B. subtilis FlgM is in a more compacted conformation than the other two. The P. aeruginosa and P. mirabilis FlgM proteins exist in a currently unknown conformation that is not either coil-like or premolten globule-like. The P. aeruginosa FlgM appears to contain more weak intramolecular contacts given its more compacted state than the P. mirabilis FlgM. These results provide experimental evidence that members of the same protein family can exhibit different degrees of disorder, though understanding how different disordered states evolve in the same protein family will require more study.