The comparison of crystal structures of lanthanide complexes with 3,12-bis(carboxymethyl)-6,9-dioxa-3,12-diazatetradecanedioic acid (H 4egta)

Abstract

Nine lanthanide complexes with 3,12-bis(carboxymethyl)-6,9-dioxa-3,12-diazatetradecanedioic acid (H 4egta): [M′(H 2O) n ][M(egta)(H 2O)] 2· nH 2O (M′: Ca, Sr; M: La, Ce, Pr, Dy, Ho, Er) have been prepared and characterized by using their infrared absorption and Raman spectra, magnetic susceptibility and thermal analyses. The results of Raman spectra (600–200 cm −1) suggest that these complexes are of two types: the first includes La, Ce, and Pr complexes, and the second Dy, Ho and Er complexes. The crystal and molecular structures of [Ca(H 2O) 2][La(egta)(H 2O)] 2·8H 2O ( 1), [Ca(H 2O) 2][Ce(egta)(H 2O)] 2·6H 2O ( 2), [Sr(H 2O) 3][Dy(egta)(H 2O)] 2·7H 2O ( 3), and [Sr(H 2O) 3][Ho(egta)(H 2O)] 2·7H 2O ( 4) have been determined by a single-crystal X-ray diffraction method. The crystals of complexes ( 1) and ( 2) are iso-morphous to each other: monoclinic, space group P2 1/ c, Z=2. The central lanthanide metal atom is 10-coordinated, in a distorted bicapped square antiprism geometry, to two nitrogen and six oxygen atoms of egta 4−, a water molecule, and a carboxyl oxygen atom from an adjacent complex ion. The Ca 2+ is at the center of the octahedral geometry and ligated by four carboxyl oxygen atoms and two water molecules. Complexes ( 3) and ( 4) are iso-morphous to each other: monoclinic, space group P2 1/ n, Z=4. The central lanthanide metal atom is nine-coordinated, in a distorted tricapped trigonal prism geometry, to two nitrogen and six oxygen atoms of egta 4−, and to a water molecule which bridges to the Sr 2+ ion. Two carboxyl groups of [M(egta)(H 2O)] − (M: Dy, Ho) complex ion bridge to the single Sr 2+ ion. In addition, the Sr 2+ is coordinated by three non-bridged water molecules, and then the Sr 2+ is coordinated by nine atoms. A relationship has been found between the average M–N, M–O(ether) and M–O(carboxylate) bond lengths and Shannon's metal crystal radii for a series of complexes shown as [M′(H 2O) n ][M(egta)(H 2O)] 2· nH 2O (M′: Ca, Sr; M: La, Ce, Nd, Dy, Ho, Er).