STRUCTURE OF 1,4,7,10-TETRAAZACYCLODODECANE TRIHYDRATE

The neutral 1,4,7,10-tetraazacyclododecane molecules exhibit crystallographic twofold rotation symmetry and have a [3333] quadrangular conformation with C atoms occupying comer positions. The H atoms bound to the N atoms at the 1 and 7 ring positions are directed outward, away from the center of the ring, while the H atoms bound to the N atoms at the 4 and 10 ring positions are pointed inward, toward the center of the ring. Each N atom is hydrogen bonded to one water molecule. The quadrangular conformation is important in the preorganization of 1,4,7,10-tetraazacyclododecane and its derivatives prior to complexation to metal ions [(C-C)ave = 1.518(7), (C-N)ave = 1.464(3) angstrom].