Group's ties I treated as impressive (11)
I believe the answer is:
prestigious
'impressive' is the definition.
(thesaurus)
'group's ties i treated' is the wordplay.
'treated' indicates an anagram.
'groups'+'ties'+'i'='groupstiesi'
'groupstiesi' with letters rearranged gives 'PRESTIGIOUS'.
'as' acts as a link.
(Other definitions for prestigious that I've seen before include "Having glamour and influence" , "Influential" , "Having high status" .)