Hydrogen Bonding Controls the Structural Evolution in Perovskite-Related Hybrid Platinum(IV) Iodides

Abstract

We describe the solid-state structural evolution in four hybrid hexaiodoplatinate(IV) compounds, demonstrating the increasingly important role that extended hydrogen bonding plays in directing the structure across the series. The compounds are APtI, where A is one of the following amines: ammonium, NH; methylammonium, CHNH; formamidinium, CH(NH); guanidinium, C(NH). These are closely related in structure and properties to the hybrid halide perovskites of lead(II) that have recently established their prowess in optoelectronics. The first three of these compounds crystallize in the vacancy-ordered double perovskite APt□I (□ indicates a vacant site) structure in the KPtCl archetype, despite the relatively large perovskite tolerance factors involved. The last compound, (GUA)PtI, crystallizes in a vacancy-ordered variant of the hexagonal CsNiCl structure: the KMnF structure. A combination of solid-state Pt andH NMR spectroscopy and detailed density functional theory calculations helps to reveal structural trends and establish the hydrogen-bonding tendencies. The calculations and measured optical properties support the surprising observation in these iodosalt compounds that, for smaller A cations, the conduction bands are considerably disperse, despite lacking extended I-Pt-I connectivity.

Perspectives and Design Principles of Vacancy-Ordered Double Perovskite Halide Semiconductors

“…The vacancy-ordered double perovskite (NH 4 ) 2 PtI 6 is also reported to exhibit an indirect band gap of ∼2 eV arising from transitions between I 5p character at the Γ point to the Pt 5d e g states at X. 25 The reported optical gaps of other members of the hybrid Pt-I family are included in It is important to note that the fundamental band gap, determined as the energy gap between the valence band maximum and conduction band minimum, is not necessarily reflective of the true optical gap or absorption onset observed by absorption spectroscopy in some members of the vacancy-ordered double perovskite family. In the A 2 SnI 6 (A = Rb + , Cs + , CH 3 NH 3 + , CH(NH 2 ) 2 + ) series, the direct transition at the Γ point is dipole-forbidden, and thus the dominant optical absorption occurs from states slightly below the valence band edge.…”

“…11,13 Similarly to the main-group metal-halide vacancy-ordered double perovskites, the palladium and platinum-based vacancy-ordered double perovskites (NH 4 ) 2 PtI 6 and Cs 2 PdBr 6 exhibit dispersive conduction bands and relatively low electron effective masses. 24,25 In Cs 2 PdBr 6 , the conduction band minimum is derived from a hybridized electronic state of the Pd 4dz 2 orbitals with the Br 4p orbitals. 24 The relatively low electron effective mass of 0.53m 0 is therefore determined by the overlap of these hybridized states with those of the neighboring octahedra.…”

“…[49][50][51][52][53][54][55][56][57] In Rb 2 SnI 6 , lower symmetry structures are observed due to the smaller size of the Rb + ion, which is significantly underbonded in the previously reported cubic vacancy-ordered double perovskite structure; 18,58 the bond valence of the Rb + ion is significantly improved by cooperative octahedral tilting to the lower-symmetry tetragonal and monoclinic structural variants of the vacancy-ordered double perovskite structure. In the absence of cooperative octahedral tilting, anharmonic lattice dynamics may be observed when the coordination preferences of the 25 As Sn 4+ and Pt 4+ exhibit similar ionic radii (r Sn = 0.690Å, r Pt = 0.625Å), 60 octahedra. [63][64][65][66] It therefore follows that similar electron-phonon coupling processes occur in the vacancy-ordered double perovskites and may even be enhanced by the presence of relatively decoupled octahedral units.…”

Pressure‐Induced Structural Evolution and Bandgap Optimization of Lead‐Free Halide Double Perovskite (NH4)2SeBr6

“…Moreover, the optoelectronic properties can be further tuned by replacing the Cs + cation on the A site with an organic ligand such as NH 4 + or CH 3 NH 3 + . Specifically, the electronic structure can be effectively modified via coupling the ligands to the rotational dynamics of [BX 6 ] 2− octahedral units through the enhanced hydrogen‐bonding interactions with the surrounding X‐site framework . Clearly, such findings demonstrate that the optical properties of HDPs are strongly related to the specific crystal structures.…”

Chemical and Structural Diversity of Hybrid Layered Double Perovskite Halides

“…[14][15][16][17][18][19][20][21][22][23][24][25][26] Double perovskites with three-dimensionally linked octahedra have demonstrated interesting physical properties and desirable "lead-free" compositions, 27 which make them a unique class of hybrid materials. Vacancy-ordered double perovskites 28,29 can also be formed with a 4+ metal alternating with a vacancy as in Cs2SnI6. 30 By tuning the size and nature of the A cation (or combinations of cations) in 3D AMX3 perovskites, distinct classes of hybrid 2D layered perovskites can be obtained, including the so-called Ruddlesden-Popper series 31,32 and the Dion-Jacobson series 33,34 (displayed in Figure 1).…”