Experimental and theoretical investigation of crystal structure of formamidinium-copper-iodide single crystals grown from aqueous solution

Organic-inorganic hybrid crystals in a formamidinium (FA)-copper (Cu)-iodide (I) ternary system were prepared and analyzed to discover new compounds with interesting optoelectronic properties, including piezoelectrical properties. In this study, we obtained FACu(2)I(3) crystals, which were crystallized in the same structure type as that of CsCu2I3. The experimentally refined and theoretically simulated crystal structures were in good accordance with each other. The results of our analyses indicated that a paraelectric, rather than a piezoelectric, structure with centrosymmetry is the most stable phase for FACu(2)I(3) with a one-dimensional [Cu2I3](-) chain. Furthermore, FACu(2)I(3) did not exhibit any luminescence under ultraviolet illumination. The reason for the absence of luminescence properties was investigated via electronic structure simulation including consideration of hydrogen bond.

Automated summary

New organic-inorganic hybrid crystals were prepared and analyzed in a formamidinium (FA)-copper (Cu)-iodide (I) ternary system, leading to the discovery of FACu(2)I(3) crystals with a paraelectric instead of a piezoelectric structure, and showed no luminescence under ultraviolet illumination. The absence of luminescence properties was investigated through electronic structure simulation considering hydrogen bond interactions.