content_image/886582.jpg content_image/886583.jpg content_image/886584.jpg
In a preferred embodiment, the cation moiety of the for› mula: 

<img src='content_image/886582.jpg'>

is selected from the following formulae. 

<img src='content_image/886583.jpg'>

<img src='content_image/886584.jpg'>

-continued 

