Structures of a Complex Hydrazinium Lead Iodide, (N2 H5 )15 Pb3 I21 , Possessing [Pb2 I9 ]5- , [PbI6 ]4- , and I- Ions and α- and β-(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 β-(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 β-(N2 H5 )PbI3 have a 2.70 eV band-gap-like absorptions.