Preparation and Structural Characterization of the Intermediate Complex [Er{H2C8H16N4(CH2COO)3(CH2(Ph)PO2)}(H2O)2]2Cl2·xH2O in the Reaction of Er3+ and the dota-Type Ligand. an Interesting Example of Two Stereoforms of a Lanthanide Complex

The synthesis of a new H 4 do3aPPh ligand related to the 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate (dota) family is described together with its erbium(III) complexes. The complexes constitute a new type of coordination compounds within the Ln-dota family, with the macrocycle protonated and erbium ions above the ring. They represent an intermediate stage on the way from the ligand to the classical in-cavity complexes. In addition, the erbium complexes have been isolated in two stereoforms, differing mainly in the arrangement on the erbium ion. The coordination polyhedra found are dodecahedron and square antiprism.