Tridentate ligands

1,4,7-Triazacyclononane, known as "TACN" which is pronounced "tack-en," is an aza-crown ether with the formula (C2H4NH)3. TACN is derived, formally speaking, from cyclononane by replacing three equidistant CH2 groups with NH groups. TACN is one of the oligomers derived from aziridine, C2H4NH. Other members of the series include piperazine, C4H8(NH)2, and the cyclic tetramer 1,4,7,10-tetraazacyclododecane.

PMDTA ('''N,N,'',N,N-pentamethyldiethylenetriamine') is an organic compound with the formula [(CH3)2NCH2CH2]2NCH3. PMDTA is a basic, bulky, and flexible, tridentate ligand that is used in organolithium chemistry. It is a colorless liquid, although impure samples appear yellowish.

9-Crown-3, also called 1,4,7-trioxonane or 1,4,7-trioxacyclononane, is a crown ether with the formula (C2H4O)3. A colorless liquid, it is obtained in low yield by the acid-catalyzed oligomerization of ethylene oxide.