| Abstrakt: |
Photovoltaic perovskites, most notably methylammonium lead triiodide, (NH3Me)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 N2H5+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 [Pb2I9]5−, [PbI6]4−, and I− ions. IR spectroscopy indicates the presence of hydrogen-bonded N2H5+ and the composition was determined by single-crystal X-ray diffraction, density measurements, combustion elemental analysis, and thermogravimetric analysis to be (N2H5)15Pb3I21, 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 (N2H5)PbI3, but neither exhibits the cubic Perovskite structure type. The structures of α- and β-(N2H5)PbI3 possess parallel ribbons of Pb2I4 and chains of PbI2, respectively. Strong inter-hydrazinium hydrogen bonding due to it possessing both hydrogen bonding donor and acceptor sites (unlike NH3Me+) appear to stabilize the observed extended ribbon motif for (N2H5)15Pb3I21 and α-(N2H5)PbI3. (N2H5)15Pb3I21 has a band-gap-like absorption of 2.34 eV, and both α- and β-(N2H5)PbI3 have a 2.70 eV band-gap-like absorptions. [ABSTRACT FROM AUTHOR] |
