| Abstract
| - The synthesis, crystal structures, and magnetic properties of a series of lanthanum(III) and gadolinium(III) complexes, involving either two or four chelating nitronyl nitroxide radical ligands, are reported. For all the gadolinium(III) compounds the analysis of the magnetic behaviors evidence antiferromagnetic GdIII-radical interactions.
- This paper reports the synthesis, crystal structures, and magnetic properties of a series of lanthanide complexeswith nitronyl nitroxide radicals of general formula {[LnIII(radical)4]·(ClO4)3·(H2O)x·(THF)y} (1−4) and [LnIII(radical)2(NO3)3] (5, 6) [Ln = La (compounds 1, 3, 5) or Gd (compounds 2, 4, and 6); radical = 2-(2‘-benzymidazolyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (NITBzImH, compounds 1, 2, 5, 6) or 2-{2‘-[(6‘-methyl)benzymidazolyl]}-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (NITMeBzImH, compounds 3, 4)]. (1) C64H88Cl3LaN16O24, fw = 1710.76,orthorhombic, Fddd, a = 11.0682(8) Å, b = 34.240(3) Å, c = 42.787(3) Å, V = 16215(2) Å3, Z = 8, R = 0.0876,Rw = 0.2336. (2) C64H88Cl3GdN16O24, fw = 1729.10, tetragonal, P4̄2c, a = 16.0682(4) Å, b = 16.0682(4) Å,c = 18.7190(6) Å, V = 4833.0(2) Å3, R = 0.0732, Rw = 0.2218. (3) C68H94Cl3LaN16O23, fw = 1742.80, tetragonal,P4̄21m, a = 21.125(3) Å, b = 21.125(3) Å, c = 10.938(2) Å, V = 4881.5(14) Å3, R = 0.1017, Rw = 0.3126. (5)C28H34LaN11O13, fw = 871.57, orthorhombic, Pna21, a = 19.5002(12) Å, b = 13.0582(8) Å, c = 14.5741(9) Å,V = 3711.1(4) Å3, R = 0.0331, Rw = 0.1146. (6) C28H34GdN11O13, fw = 889.91, orthorhombic, Pna21, a =19.1831(10) Å, b = 13.1600(7) Å, c = 14.4107(7) Å, V = 3638.0(3) Å3, Z = 4, R = 0.0206, Rw = 0.0625.Compounds 1−4 consist of [MIII(radical)4]3+ cations, uncoordinated perchlorate anions, THF, and water crystallizationmolecules. In these complexes, the coordination number around the lanthanide ion is eight, and the polyhedron iseither a distorted dodecahedron (1) or a distorted cube (2, 3). The crystal structures of 5 and 6 consist of independent[MIII(radical)2(NO3)3] entities in which the lanthanide is ten-coordinated and has a distorted bicapped square antiprismcoordination polyhedron. For the lanthanum(III) complexes, the temperature dependence of the magnetic susceptibilityindicates that radical−radical magnetic interactions are negligible either for compounds 1 and 3, while for compound5 it is simulated considering dimers of weakly antiferromagnetically coupled radicals (Jrad-rad = −1.1 cm-1). In thecase of the gadolinium(III) compounds (2, 4, 6), each magnetic behavior gives unambiguous evidence ofantiferromagnetic GdIII−radical interaction (2, JGd-rad = −1.8 cm-1; 4, JGd-rad = −3.8 cm-1; 6, JGd-rad1 = −4.05cm-1 and JGd-rad2 = −0.80 cm-1), in contrast to the ferromagnetic case generally observed. The nature of theGdIII−radical interaction is explained in relation to the donor strength of the free radical ligand.
|
