1,4,7-Triazacyclononane
1 , 4 , 7-Triazacyclononane , known as "TACN" which is pronounced "tack-en , " is an aza-crown ether with the formula ( C2H4NH ) 3 . 
<triplet> 1,4,7-Triazacyclononane <subj> aza-crown ether <obj> instance of