How Strong Is the Hydrogen Bond in Hybrid Perovskites?

[Image: see text] Hybrid organic–inorganic perovskites represent a special class of metal–organic framework where a molecular cation is encased in an anionic cage. The molecule–cage interaction influences phase stability, phase transformations, and the molecular dynamics. We examine the hydrogen bonding in four AmBX(3) formate perovskites: [Am]Zn(HCOO)(3), with Am(+) = hydrazinium (NH(2)NH(3)(+)), guanidinium (C(NH(2))(3)(+)), dimethylammonium (CH(3))(2)NH(2)(+), and azetidinium (CH(2))(3)NH(2)(+). We develop a scheme to quantify the strength of hydrogen bonding in these systems from first-principles, which separates the electrostatic interactions between the amine (Am(+)) and the BX(3)(–) cage. The hydrogen-bonding strengths of formate perovskites range from 0.36 to 1.40 eV/cation (8–32 kcalmol(–1)). Complementary solid-state nuclear magnetic resonance spectroscopy confirms that strong hydrogen bonding hinders cation mobility. Application of the procedure to hybrid lead halide perovskites (X = Cl, Br, I, Am(+) = CH(3)NH(3)(+), CH(NH(2))(2)(+)) shows that these compounds have significantly weaker hydrogen-bonding energies of 0.09 to 0.27 eV/cation (2–6 kcalmol(–1)), correlating with lower order–disorder transition temperatures.