Halogen nuclear quadrupole resonance and structural relationships in some complex halides of zinc and copper

Abstract

X-ray diffraction and halogen nuclear quadrupole resonance (n.q.r.) methods show that Rb₃ZnBr₅, (NH₄)₃ZnBr₅, and CsZnI₅ are isostructural with orthorhombic (NH₄)₃ZnCl₅, and that Rb₃ZnCl₅ has the tetragonal Cs₃CoCl₅ structure. ZnI₂,2NH₃ is isomorphous with the corresponding chloride and bromide diammines. Rb₂ZnBr₄ and (NH₄)₂ZnBr₄ have structures of Cs₂ZnBr₄ type, although the rubidium salt shows some stacking faults. In the complex chlorides ³⁵Cl n.q.r. frequencies are grouped about 9 MHz, while the bromides have ⁸¹Br frequencies grouped around 60 MHz. The ½ → 3/2 transitions of ¹²⁷I in the iodides are in the region of 76 MHz. The diammine compounds ZnBr₂,2NH₃ and ZnI₂,2NH₃ have frequencies close to the mean values for the ZnBr₄^2- and ZnI₄^2- ions respectively, but in the hydrates ZnCl₂,l⅓H₂O,ZnBr₂,2H₂O, β-KZnBr₃,2H₂O, and KZnI₃,2H₂O the halogen frequencies are increased. N.q.r. and X-ray data are also reported for the compound Cs₃CuCl₅, formed by quenching the melt. This compound slowly disproportionates at room temperature into Cs₂CuCl₄ and CsCl.