On the polymorphism of In5Br7

The existence of two polymorphs of In5Br7 has been proved by single crystal structure determinations. In5Br7 (tP192) crystallizes with the tetragonal space group P4(1)2(1)2 and lattice parameters a(t) = 1318.9(5) pm and c(t) = 3723.8(9)pm (293 K). Concerning monoclinic In5Br7 (mC192), the centrosymm etric space group C2/c with lattice parameters a(m) = 1867.3(4) pm, b(m) = 1867.0(5) pm, c(m) = 1918.0(7) pm, and beta(m) = 103.96(2)degrees (293 K) h as been con firmed. Both modifications of In5Br7 are built up from layers o f the same type. These layers with a thickness of about 930 pm consist of s tructure fragments [(In6Br2)-Br-I](4+) and [(IN4Br12)-Br-II](4-). The anion is composed of two ethan-like [(In2Br6)-Br-II](2-) units, which contain In -In bonds. The stacking sequence of the layers with symmetry C 12 (1) diffe rs for the two modifications of In5Br7. The tetragonal form is generated by applying a 4(1) screw axis; the monoclinic polymorph is formed by introduc ing inversion centers between the layers. The adequate name of IN5Br7 = IN3 I[(IN2Br6)-Br-II]Br is triindium(I)-hexabromodiindate(II) (In-In)-bromide.