First Full Structural Characterization of Chloro Formamidinium Salts

Abstract

While the synthesis of chloro formamidinium chloride has been known for over one century, no solid‐state structure of a chlorine‐substituted formamidinium compound has been reported up to now. Herein, we describe syntheses, solid‐state structures, and vibrational properties of four chloro formamidinium compounds, namely [ClC(NH2)2]Cl (1), [ClC(NH2)2](AuCl4) (2), [ClC(NH2)2]2(PdCl4) (3), and [ClC(NH2)2]2(PtCl6) (4), as determined by single‐crystal X‐ray diffraction (SCXRD). 1 and 3 crystallize in the monoclinic space group P21/c, 2 in the orthorhombic space group Pbcn, whereas 4 adopts the triclinic space group P1. By using a combination of high‐resolution time‐of‐flight neutron powder diffraction, state‐of‐the‐art DFT calculations as well as IR spectroscopy, the prior SCXRD result was fully confirmed and augmented by determining the hydrogen‐bonded molecular networks. First‐principles electronic‐structure calculations corroborate the ionic nature of these salts by showing very flat, molecular‐like bands next to the Fermi level, in addition to indirect bandgaps. This study underlines the upmost importance of complementing diffraction data by ab initio calculations, as theory‐derived anisotropic displacement parameters served as fixed numerical entries.