I haven't come across this term before (as C.P.Snow said of television, "No good can come of this device; the word is half Greek and half Latin"), but looking at the abstracts that come up on Google, it seems to denote a ligand that (unlike a usual multidentate ligand such as EDTA) has two (or more?) different types of binding site that can simultaneously bind different types of metal ions, e.g. the example O,O'-bisnicotinic acid tetraethylene glycol, where the Os bind to alkaline earth metal cations and the pyridinic Ns bind to Group 11 cations. I guess there may be a definition of "multitopic ligand" in the full paper, but I can't access it without paying. It would be worth your while to do so if this is a real interest, rather than just seeing the term in passing and wondering what it meant.