Structures of a Complex Hydrazinium Lead Iodide, (N₂H₅)₁₅Pb₃I₂₁, Possessing [Pb₂I₉]⁵⁻, [PbI₆]⁴⁻, and I⁻ Ions and α‐ and β‐(N₂H₅)PbI₃

Abstract

Abstract Photovoltaic perovskites, most notably methylammonium lead triiodide, (NH 3 Me)PbI 3 , 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 N 2 H 5 + I − with PbI 2 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 ( P 6 3 /m: a= 10.8906(10) Å; b= 37.845(5) Å) crystals possess isolated face‐sharing octahedral [Pb 2 I 9 ] 5− , [PbI 6 ] 4− , and I − ions. IR spectroscopy indicates the presence of hydrogen‐bonded N 2 H 5 + and the composition was determined by single‐crystal X‐ray diffraction, density measurements, combustion elemental analysis, and thermogravimetric analysis to be (N 2 H 5 ) 15 Pb 3 I 21 , 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 ( P 6 3 / mmc : a= 8.7386(9) Å; b= 8.2006(9) Å) unit cells, respectively, possessing the perovskite ABX 3 composition of (N 2 H 5 )PbI 3 , but neither exhibits the cubic Perovskite structure type. The structures of α‐ and β‐(N 2 H 5 )PbI 3 possess parallel ribbons of Pb 2 I 4 and chains of PbI 2 , respectively. Strong inter‐hydrazinium hydrogen bonding due to it possessing both hydrogen bonding donor and acceptor sites (unlike NH 3 Me + ) appear to stabilize the observed extended ribbon motif for (N 2 H 5 ) 15 Pb 3 I 21 and α‐(N 2 H 5 )PbI 3 . (N 2 H 5 ) 15 Pb 3 I 21 has a band‐gap‐like absorption of 2.34 eV, and both α‐ and β‐(N 2 H 5 )PbI 3 have a 2.70 eV band‐gap‐like absorptions.