Optical absorption spectra (5ndash;26 kK) of fused mixtures of CsCl and NiCl2containing 2ndash;60 mole NiCl2were measured at about 860deg;C and a mixture containing 20 mole NiCl2was studied at 560deg;mdash;862deg;C. Up to 20 mole NiCl2the Bouguermdash;Beer law was accurately obeyed, and each nickel was tetrahedrally coordinated to four chlorides. At higher NiCl2contents, nickel coordination was partitioned between tetrahedral and other (unidentified) geometries. The fraction with tetrahedral coordination progressively decreased with increasing NiCl2content but was still appreciable at 60 mole NiCl2. The most prominent feature of the spectrum associated with the unidentified geometries was a band between 18 and 19 kK. These results indicate that nickel has very similar coordination geometries in the liquid and crystalline phases of Cs3NiCl5but very different coordination geometries in crystalline and liquid CsNiCl3.
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