Isomers of 1,4,8,11-Tetraazacyclotetradecane-6,13-dicarboxylate Characterized as Cobalt(III) Complexes

Abstract

The major trans (1) and minor cis (2) isomers of 1,4,8,11-tetraazacyclotetradecane-6,13-dicarboxylate have been characterized as the complexes [Co(1)](ClO₄) and [Co(H2)(OH₂)]Cl(ClO₄)·H₂O. The former crystallized in the C2/c space group and the latter in the P2₁/c space group, with cell parameters a 16.258(7), b 9.050(3), c 15.413(6) Å, β133.29(3)°, and a 9.694(4), b 16.135(1), c 12.973(5) Å, β 93.00(2)°, respectively. Their characterization completes identification of the respective trans and cis isomers for the series of c-pendant macrocycles also including 1,4,8,11-tetraazacyclotetradecane-6-amine-13-carboxylate ((3), (4)) and 1,4,8,11-tetraazacyclotetradecane-6,13-diamine ((5), (6)). The complexes show limited distortion from octahedral geometry with the strain in the presence of the coordinated c-pendant carboxylate significantly reduced compared with that for the c-pendant amine in analogues, a consequence mainly of six-membered as opposed to five-membered chelate rings involving the pendant donor. A comparison of the physical properties for the trans isomers of the octahedral complexes of (1), (3), and (5), which reflect progressively increasing strain, is presented.