X‐Ray and Transmission Electron Microscopy Investigations of the New Solids In5S5Cl, In₅Se₅Cl, In₅S₅Br, and In₅Se₅Br

The compounds In 5 Ch 5 X (Ch = S, Se; X = Cl, Br) represent new mixed valence solids with indium occurring simultaneously in three different oxidation states: In + , In 3+ and In 2+ where the latter appears as covalently bonded dumbbells (In 2 ) 4+ . Although the ionic formulation ( In 5 Ch 5 X = In + 2In 3+ (In 2 ) 4+ 5Ch 2— X — ) is the same for all compounds, they crystallise in two structure types (In 5 Ch 5 Cl‐type: monoclinic, P 2 1 / m , Z = 2; In 5 Ch 5 Br‐type: orthorhombic, Pmn 2 1 , Z = 2). Ignoring the distribution of the halogen atoms, the anionic partial structure is very similar in both structure types. The main difference is an exchange of (In + ) by (In 2 ) 4+ and vice versa on selected positions. This is possible due to the nearly identical coordination of both ions (tri‐capped trigonal prisms). HRTEM investigations show remarkable differences in the real structures of In 5 Ch 5 Cl and In 5 Ch 5 Br. In contrast to the perfectly ordered crystals of the bromides, the chlorides exhibit a variety of nanoscaled crystal defects, i.e. twinning, polylamellar intergrowth of polymorphs and lamellar intergrowth of structurally related compounds as demonstrated in In 5 S 5 Cl/In 6 S 7 . The occurrence of these defects is discussed using an appropriate structure model.