What is the difference? I know about di and bi but not about bi and bis.
Go here and scroll to the bottom. Click on the definitive rules link and download the pdf. On page 0.31 0.32 in the preamble the use of bis vs bi, tris vs tri, etc is discussed. Generally, bis, tris, tetrakis, etc., are used to remove ambiguity when the use of bi, tri, tetra and so forth, would result in confusion.
When in doubt, use bis rather than bi when describing substitution on metals.
Separate names with a comma.