Design and Magnetic Properties of a Magnetically Isolated Gd^IIICu^II Pair. Crystal Structures of [Gd(hfa)₃Cu(salen)], [Y(hfa)₃Cu(salen)], [Gd(hfa)₃Cu(salen)(Meim)], and [La(hfa)₃(H₂O)Cu(salen)] [hfa = Hexafluoroacetylacetonato, salen = <i>N</i>,<i>N</i>‘-Ethylenebis(salicylideneaminato), Meim = 1-Methylimidazole]

Abstract

The crystal structures of three compounds have been determined at room temperature, namely [Gd(hfa)3Cu(salen)] (1), [Y(hfa)3Cu(salen)] (2), and [Gd(hfa)3Cu(salen)(Meim)] (3), and the crystal structure of a fourth compound, [La(hfa)3(H2O)Cu(salen)] (4), has been determined at −100 °C; hfa = hexafluoroacetylacetonato, salen = N,N‘-ethylenebis(salicylideneaminato), and Meim = 1-methylimidazole. [La(hfa)3Ni(salen)] (5), isomorphous with 1, has also been synthesized. 1 crystallizes in the monoclinic system, space group P21/n, with a = 17.292(5) Å, b = 22.370(5) Å, c = 19.658(6) Å, β = 90.07(2)°, and Z = 8. 2 crystallizes in the triclinic system, space group P1̄, with a = 12.207(3) Å, b = 13.019() Å, c = 13.011(6) Å, α = 82.87(4)°, β = 83.55(3)°, γ = 70.91(3)°, Z = 2. 3 crystallizes in the monoclinic system, space group P21/n, with a = 16.521(9) Å, b = 20.381(5) Å, c = 12.758(6)°, β = 93.22(6)°, and Z = 4. 4 crystallizes in the monoclinic system, space group P21/n, with a = 12.826(2) Å, b = 23.067(8) Å, c = 13.081(3) Å, β = 91.37(2)°, and Z = 4. The structures of 1, 2, and 4 consist of dimers of binuclear units in which the metal ions are bridged by the oxygen atoms of the salen ligand, with rather short Cu−Cu intermolecular separations (3.630(3) Å for 1, 4.251(2) Å for 2, and 3.620(2) Å for 4). The GdIII ion in 1 and the YIII ion in 2 have a square antiprismatic environment, while the LaIII ion in 4 is nine-coordinate with a water molecule in the LaIII coordination polyhedron. In compounds 1, 2, and 4 the CuII ion has a square planar environment. The Gd−Cu distances are 3.198(2) and 3.231(2) Å for 1, the Y−Cu distance is 3.257(1) Å for 2, and the La−Cu distance is 3.381(2) Å for 4. The structure of 3 consists of perfectly isolated binuclear species, the Meim ligand occupying a peripheral apical position in the copper coordination sphere. The magnetic properties of 1 and 3 have been investigated. They have revealed GdIII−CuII ferromagnetic interactions. The ground state of 3 is an S = 4 state, stabilized by 5.68 cm-1 with respect to the S = 3 excited state. The situation is more complicated for 1, due to the presence of Cu−Cu intermolecular interactions.