Once a smart complex in state capital (10)
I believe the answer is:
sacramento
'state capital' is the definition.
(Sacramento is an example)
'once a smart complex' is the wordplay.
'complex' is an anagram indicator.
'once'+'a'+'smart'='onceasmart'
'onceasmart' anagrammed gives 'SACRAMENTO'.
'in' is the link.
(Other definitions for sacramento that I've seen before include "port" , "US city" , "State capital of California" .)