I^–/I₃^– Redox-Assisted Synthesis and Properties of Low Dimensional, Mixed-Valent Gold Iodide Perovskite Derivatives

Abstract

We report a set of three new mixed-valent Au I Au III iodides: (ClPy) 3 [AuI 2 ] 2 [AuI 4 ] [1], (BrPy) 3 [AuI 2 ] 2 [AuI 4 ] [2], and (ClPy) 2 [AuI 2 ][AuI 4 ] [3], as well as three new monovalent Au III iodides: (XPy) 2 [AuI 4 ][I 3 ] (Py = 4-X-pyridinium X = Cl, Br, and I) [4−6]. Two of these mixed-valent compounds (1 and 2) incorporate both monovalent Au I •••Au I (aurophilic bonding) and mixed-valent Au I I•••Au III I couples (Au−I halogen bonding), to the best of our knowledge an unprecedented structural feature. These same two mixed-valent compounds also exhibit a rare lowdimensional molecular architecture with respect to second sphere Au•••I interactions, namely, 1D chains of Au•••I interactions, extending along a single crystallographic axis. All compounds were synthesized with the assistance of the I − /I 3 − redox couple and tacit manipulation of the polyiodide content during synthesis. Air-free synthesis was used to influence the redox process of I 3 − /I − , resulting in better selection for mixed-valent products. Compounds 1−2 and 4−5 exhibit a characteristically narrow bandgap (1.04−1.25 eV), as measured via diffuse reflectance spectroscopy (DRS). Computational analyses were used to rationalize the specific assembly modes of [AuI 2 ] − and [AuI 4 ] − species, and they show that the Au I •••I interaction type is favored over the Au III •••I.