Hybrid Organic Lead Iodides: Role of Organic Cation Structure in Obtaining 1D Chains of Face-Sharing Octahedra vs 2D Perovskites

((R­(CH2)nNH3+ cations
(R = aryl, substituted cyclohexyl; n = 1, 2) can
form hybrid lead iodides that include both 2D layered
perovskites of formula [R­(CH2)nNH3]2PbI4 and 1D structures consisting
of 1D wires of face-sharing PbI6 octahedra and having the
formula [R­(CH2)nNH3]­PbI3 (face-sharing lead iodide chains, FSLICs). Using
a series of such cations, we find that 1D FSLIC formation is favored
when hydrogen bonding is possible between the ammonium moiety of one
cation and a hydrogen-bond acceptor substituent of the same or another
cation. A total of 16 new hybrid organic lead iodide crystal structures,
11 of which are FSLICs, are reported. The FSLIC structures can be
further categorized according to the arrangement of neighboring wires.
The optical properties of these materials are largely insensitive
to the identity of the organic cations and to the resulting structural
details. However, there is a correlation between the exciton energy
and the pattern in which the wires are arranged relative to one another.
Density functional theory calculations indicate that the dispersion
at the top of the valence band varies depending on the relative wire
arrangement.