Four Discrete Silver Iodobismuthates/Bromobismuthates with Metal Complexes: Syntheses, Structures, Photocurrent Responses, and Theoretical Studies

Using in situ formed metal complexes of [Fe(bipy)3]2+ or [Ni(bipy)3]2+ (bipy = 2,2′-bipyridine) as templates, four new Ag–Bi–X (X = I and Br) compounds are first isolated in the metal-complex-decorated heterometallic halobismuthate family, namely [M(bipy)3]AgBiI6 (M = Fe (1), Ni (2)), [Fe(bipy)3]AgBiBr6 (3), and [Ni(bipy)3]AgBiBr6 (4). Compounds 1–4 feature discrete [AgBiX6]n2n– anions, exhibiting three polymorphisms that may be ascribed to the different stackings and the flexible condensations of [BiX6] octahedrons and [AgX4] tetrahedra/[AgX3] triangles. UV–vis diffuse reflectance analyses reveal that they are narrow band gap semiconductor materials (ca. 1.82–2.13 eV). Intriguingly, the title compounds display excellent photoelectrical switching properties, with photocurrent density following the order 3 > 4 > 2 > 1. In addition, the comparative studies of intermolecular interactions, theoretical band structures, density of states, and effective masses of three polymorphisms have also been investigated.