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Crystal structure of anhydrous zinc bromide

1984; De Gruyter; Volume: 166; Issue: 3-4 Linguagem: Inglês

10.1524/zkri.1984.166.3-4.189

2196-7105

Chung Chieh, Mary Anne White,

Luminescence Properties of Advanced Materials

Abstract The crystal structure of ZnBr 2 is tetragonal, space group I 4 1 / acd , a = 11.389(4), c = 21.773(9) Å, V = 2826(3) A 3 , μ = 308.2 cm −1 . D m = 4.208, Z = 32, D x = 4.233 Mg m −3 . The structure was determined from 146 independent observed [ F > 2 σ ( F )] reflections to an R value of 0.074. The bromide ions are arranged in an fcc array with Zn atoms filling in 1/4 of the tetrahedral sites. This results in the formation of ‘super-tetrahedral’ groups of Zn 4 Br 6 Br 4/2 , which again interconnect to give a three-dimensional network. These groups are similar to those of P 4 O 10 , hexamethylenetetramine, [N 4 (CH 2 ) 6 ], and the large ‘cage’, Zn 4 S 6/2 S 4/4 , present in the zinc blende structure. However, the cage groups in ZnBr 2 have point group [unk] in this space group and they are only slightly deviated from [unk]3 m , the point group for idealized cages. The mean Zn – Br distance is 2.42(1) Å, and the mean Br – Zn – Br angle is 109(3)°. All the Br atoms are 2-coordinated, with Zn – Br – Zn angles ranging from a mean value of 105.3(3) for intracage bonds to 107.9(5)° for intercage connections. The ZnBr 2 structure is related to those of HgI 2 , Be 3 P 2 and Cd 3 As 2 in a very interesting way.