Das Lanthaniodidethanid o ‐La 5 I 9 (C 2 ) – Die orthorhombische Hochtemperaturmodifikation

The Lanthanumiodideethanide o ‐La 5 I 9 (C 2 ) – The Orthorhombic High Temperature Modification o ‐La 5 I 9 (C 2 ) is synthesized by reaction of LaI 3 , La metal and graphite powder in sealed Ta containers at 850 °C < T < 900 °C. It crystallizes in the orthorhombic space group Pbca with a = 8.0247(16) Å, b = 16.887(3) Å, c = 35.886(7) Å. o ‐Ce 5 I 9 (C 2 ) is isotypic with the lattice parameters a = 7.9284(4) Å, b = 16.714(1) Å, c = 35.530(3) Å. o ‐La 5 I 9 (C 2 ) transforms at 800 °C to the triclinic low temperature modification t ‐La 5 I 9 (C 2 ). The transformation is reversible. The La atoms form trigonal bipyramids centered by C 2 groups. These units are connected by iodine atoms above the faces (f), edges (e) and corners according to La 5 (C 2 )I(f) i I(e) i−i 2/2 I(e) i−a 7/2 I(e) a−i 7/2 . The C‐C distance in the C 2 unit is 1.45(2) Å. The crystals with greenish luster are moisture sensitive.