Denis Wessner

Rare earth complexes with neutral macrocyclic ligands

Stoechiometrie, proprietes magnetiques et structurales. Etude en solution des complexes des ions Ln(III); constantes de stabilite

Crystal structure and emission spectrum of tris(nitrato)-1,4,7,10-tetraozacyclododecane-Europium(III) ☆

Abstract The crystal and molecular structure of the title compound was determined from single crystal X-ray diffraction. The complex crystallizes in the monoclinic space group P 2 1 /c, with Z = 4. Lattice parameters are: a = 12.121(3), b = 8.556(2), c = 15.269(4) A and β = 91.86(2)°. The structure was solved by Patterson and Fourier techniques and refined by least-squares to a final conventional R value of 0.079. The europium(III) ion is 10-coordinate, being bonded to three bidentate nitrate groups and to the four oxygen atoms of the crown ether. The EuO distances are in the range in the range 2.41–2.57 A (average: 2.49(5) A . The nitrate groups are planar with NO bond lengths between 1.21 and 1.29 A . The coordination polyhedron of Eu(III) is discussed. The effective ionic radius of the 10-coordinate Eu(III) ion is 1.178 A .

Complexes of the Heavier Lanthanoid Nitrates with Crown Ethers

Crown ethers form stable complexes with lanthanoid (III) ions (2), (3), (4), (5). We have shown, in previous papers of this series, that unsolvated complexes of the lighter lanthanoid nitrates (Ln = La−Gd) can be isolated with 15-crown-5 and 18-crown-6 ethers. The Ln(III)/crown ether ratio is 1:1 for the complexes with ligand 2 whereas complexes of ligand 3 may have two different stoichiometries, 1:1 for Ln = La−Nd and 4:3 for Ln = La−Gd (6). The strength of the Ln(III)/crown ether interaction depends on both the ratio of ionic diameter/ligand cavity diameter and the ligand flexibility. In this communication we discuss the interaction of ligands 2 and 3 with the heavier lanthanoid (III) ions and we report the results of a 1H-NMR study of the 18-crown-6 complexes with Ln = La, Pr, Nd, Eu, Yb, as well as some preliminary results of our X-ray structural work on the neodymium nitrate 1:1 and 4:3 complexes with 18-corn-6.

Thermogravimetric Study of Lanthanoid(III) Complexes with Crown Ethers

Lanthanoid(III) ions interact with crown ethers 1 to 3 to yield stable coordination compounds. Ligands 1 and 2 form 1:1 complexes with all the lanthanoid nitrates, and 1:2 complexes with the lighter lanthanoid perchlorates (Ln=La-Gd) [2][3]. With ligand 3, complexes having a salt:ligand ratio of 1:1 and 4:3 can both be isolated. The latter compounds either crystallize directly out of equimolar solutions of nitrate and ligand in acetonitrile (Ln=Nd-Gd,Dy) or can be obtained by thermal decomposition of the corresponding 1:1 complexes [2]. We have thus investigated the thermal behaviour of all the lanthanoid nitrate 1:1 complexes we have isolated with ligands 1 to 3 in order to determine which complexes decompose into the 4:3 compounds. We have also measured the heat of some 1:1 → 4:3 transformations by means of differential scanning calorimetry.

Choosing a coordination number for Ln(III): 1:1, 1:2, 2:1, 3:2 and 4:3 complexes with crown ethers

The stoichiometry of the complexes between rare earth salts and crown ethers depends on the nature of both the macrocycle and the counteranion, as shown in the Table (1).