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

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journal contribution
posted on 03.08.2018, 14:20 by Hayden A. Evans, Douglas H. Fabini, Jessica L. Andrews, Mitchell Koerner, Molleigh B. Preefer, Guang Wu, Fred Wudl, Anthony K. Cheetham, Ram Seshadri
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 A2PtI6, where A is one of the following amines: ammonium, NH4+; methylammonium, CH3NH3+; formamidinium, CH­(NH2)2+; guanidinium, C­(NH2)3+. 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 A2Pt□I6 (□ indicates a vacant site) structure in the K2PtCl6 archetype, despite the relatively large perovskite tolerance factors involved. The last compound, (GUA)2PtI6, crystallizes in a vacancy-ordered variant of the hexagonal CsNiCl3 structure: the K2MnF6 structure. A combination of solid-state 195Pt and 1H 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.