The X-ray structure of 1,4,8,11-tetraazacyclotetradecane-1,4,8,11- tetraacetic acid and its relevance to the protonation of polyaza polycarboxylic macrocycles
The tetraprotonated form of the macrocyclic ligand teta (1,4,8,11- tetraazacyclotetradecane-1,4,8,11-tetraacetate) crystallises in the monoclinic system, space group P2(1)/c, a = 7.816(2), b = 14.656(2), c = 11.647(3) Angstroms, beta = 102.52(4) , Z = 2. The structure was refined from diffractometer data to an R value of 0.035 and the hydrogen atoms were located unequivocally. In agreement with previous NMR investigations, H(4)teta features two protonated nitrogen atoms in the ring and two protonated carboxylate groups. The electrostatic repulsion is thus reduced to a minimum. The tetraaza ring adopts a quadrangular  conformation which is one of the most stable geometric arrangements of the 14-membered cycles. The ligand forms no intramolecular hydrogen bonds but is involved in intermolecular hydrogen bonds with water molecules.
Bibliographic Reference: Article: Journal of the Chemical Society - Dalton Transactions (1991) pp. 2477-2481
Record Number: 199111489 / Last updated on: 1994-12-02
Original language: en
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