|The equilibrium between octahedral and tetrahedral cobalt (II) has been studied in H20-HC1,
H20-HC/04-HC1, H20-KCNS solutions and in R20-B20 3, R20-Si02, R20-Al20 3-Si02, and Ca0-
B203-Al203 glasses. In aqueous solution, cobalt (II) absorption, in the region 10 to 25 kK, increases
with increased addition of HCl or KCNS. In R20-B20 3 and R20-Si02 glasses absorption of cobalt
(II) increases with increased addition of R20. In R20-Al20 3-Si02 and Ca0-B20 3-Al20 3 glasses the
total absorption area and the relative area of the resolved band around 15 k K (characteristic of tetrahedral
cobalt (II) decrease with increased substitution of Al20 3 for Si02 or B20 3. However, in
Ca0-B20 3-Al20 3 glasses containing a high proportion of Al20 3 and CaO, the octahedral-tetrahedral
equilibrium of cobalt (II) behaved differently.
In all the systems of solutions and glasses the total absorption area from 10 to 25 kK or the
relative area of the resolved band around 15 kK (4A2)(F) -+4T1 (P) could be used as a qualitative
measure of the octahedral-tetrahedral equilibrium of cobalt (II].