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已知镧系元素中铈、镨、钕、铽及镝可形成四价化合物。然而除铈以外,其余的四价化合物多数是用干法或由非水介质中获得的。由标准电极电位E_(M~4+/M~3+)~0可知,铈以外的四价镧系离子在水溶液中很难稳定存在,除非形成足够稳定的络合物。以前曾有过从水溶液中获得Pr(Ⅳ),Nd(Ⅳ)及Tb(Ⅳ)化合物的报导,但均未被后人所重复。近年来以不饱和杂多酸盐为络合剂,从水溶液中获得了Pr(Ⅳ)和Tb(Ⅳ)的
It is known that cerium, praseodymium, neodymium, terbium and dysprosium in the lanthanides form tetravalent compounds. However, with the exception of cerium, the majority of the remaining tetravalent compounds are obtained from dry or non-aqueous media. From the standard electrode potentials E_ (M ~ 4 + / M ~ 3 +) ~ 0, it is found that tetravalent lanthanide ions other than cerium are hardly stable in aqueous solution unless a sufficiently stable complex is formed. There have been reports of Pr (IV), Nd (IV) and Tb (IV) compounds obtained from aqueous solutions before, but none have been repeated by the latter. In recent years, unsaturated heteropoly acid salt as a complexing agent, obtained from the aqueous solution of Pr (Ⅳ) and Tb (Ⅳ)