Electron Paramagnetic Resonance Study of Copper(II) Fluosilicate Hexahydrate
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An electron paramagnetic resonance study was performed on single crystals of copper
fluosilicate hexahydrate. EPR signals correspond to three tetragonally distorted pctahedral
Cu(II) ions (A site) with g values: g11 = 2.390, gJ. .= 2.093, and ·one regular
octahedral Cu(II) ion (B site) with g = 2.093. The spectra are thus quite different
from those observed earlier by Bleaney and Ingram in Cu(II):ZnSiF6 • 6H20.
Fluosilicate hexahydrates of divalent metals belong to a series of crystals wellsuited
for X-ray, magnetic susceptibility and anisotropy, electron paramagnetic
resonance, optical, and other studies (J-4). Observations of an isotropic EPR signal
at 90 K and above and anisotropic EPR signals at 20 K by Bleaney and Ingram
(J) in Cu:ZnSiF6 • 6H20 provided the first experimental evidence of the Jahn-Teller
effect. A determination of crystal structures of this series by Ray eta/. (2, 3) has
revealed that copper(II) fluosilicate hexahydrate (3), contrary to earlier belief, is
not isomorphous with zinc fluosilicate hexahydrate. The structure is still rhombohedral
(space group R3) with a cell four times as large as that supposed earlier.
The unit cell, which has dimensions a = b = 18.18 A and c = 9.857 A, contains
three magnetically nonequivalent tetragonally distorted Cu(II) · 6H20 octahedra
(Cu-0(1) = 1.97 A, Cu-0(2) = 1.97 A, Cu-0(3) = 2.367 A) designated as the
A sites; and one regular Cu(II) · 6H20 octahedron (Cu-0 = 2.074 A) designated
as the B site. It was therefore considered of interest to study EPR in single crystals
of copper fluosilicate hexahydrate with the object of unravelling the nature of the
ligand fields in a crystal where two types of Cu(II) complexes coexist.
Keywords
Q Science (General), QC Physics