Crystal structure of new formamidinium triiodide jointly refined by single-crystal XRD, Raman scattering spectroscopy and DFT assessment of hydrogen-bond network features.

Artem A Ordinartsev,Eugene A Goodilin,Alexey B Tarasov,Konstantin A Lyssenko,Andrey A Petrov,Andrey V Petrov

doi:10.1107/s2056989021005673

Abstract

A novel triiodide phase of the formamidinium cation, CH5N2 +·I3 -, crystallizes in the triclinic space group P at a temperature of 110 K. The structure consists of two independent isolated triiodide ions located on inversion centers. The centrosymmetric character of I3 - was additionally confirmed by the observed pronounced peaks of symmetrical oscillations of I3 - at 115-116 cm-1 in Raman scattering spectra. An additional structural feature is that each terminal iodine atom is connected with three neighboring planar formamidinium cations by N-H⋯I hydrogen bonding with the N-H⋯I bond length varying from 2.81 to 3.08 Å, forming a deformed two-dimensional framework of hydrogen bonds. A Mulliken population analysis showed that the calculated charges of hydrogen atoms correlate well with hydrogen-bond lengths. The crystal studied was refined as a three-component twin with domain ratios of 0.631 (1):0.211 (1):0.158 (1).

Highlights

A novel triiodide phase of the formamidinium cation, CH5N2+ÁI3À, crystallizes in the triclinic space group P1 at a temperature of 110 K
An additional structural feature is that each terminal iodine atom is connected with three neighboring planar formamidinium cations by N— HÁ Á ÁI hydrogen bonding with the N—HÁ Á ÁI bond length varying from 2.81 to 3.08 A, forming a deformed two-dimensional framework of hydrogen bonds
Polyiodides are a large class of compounds with organic and inorganic cations and a great diversity of anion shapes varying from simple linear I3À up to I293– complexes (Svensson & Kloo, 2003)

Summary

Chemical context

Polyiodides are a large class of compounds with organic and inorganic cations and a great diversity of anion shapes varying from simple linear I3À up to I293– complexes (Svensson & Kloo, 2003). Polyiodides have attracted great interest for a wide set of applications, such as dye-sensitized solar cells (DSSC) (O‘Regan & Gratzel, 1991; Jeon et al, 2011), different electrochemical devices (Weinstein et al, 2008; Weng et al, 2017) and light-polarizing materials (Kahr et al, 2009). Another recently proposed prospective application of polyiodides is to use liquid methylammonium and formamidinium polyiodides as a precursor for the fabrication of lightabsorbing materials for perovskite solar cells (Petrov, Belich et al, 2017). We investigated the features of the new structure of the single-crystalline CH5N2+ÁI3À (I, FAI3) phase by means of Raman scattering spectroscopy and DFT calculations

Structural commentary

Synthesis and crystallization

Refinement

Findings

DFT calculations