DESIGN AND MAGNETIC-PROPERTIES OF A MAGNETICALLY ISOLATED GDIIICUII PAIR - CRYSTAL-STRUCTURES OF [GD(HFA)(3)CU(SALEN)], [Y(HFA)(3)CU(SALEN)], [GD(HFA)(3)CU(SALEN)(MEIM)], AND [LA(HFA)(3)(H2O)CU(SALEN)] [HFA EQUALS HEXAFLUOROACETYLACETONATO, SALEN EQUALS N,N'-ETHYLENEBIS(SALICYLIDENEAMINATO), MEIM EQUALS 1-METHYLIMIDAZOLE]

The crystal structures of three compounds have been determined at room temperature, namely [Gd(hfa)(3)Cu(salen)] (1), [Y(hfa)(3)Cu(salen)] ( 2), and [Gd(hfa)(3)Cu(salen)(Meim)] (3), and the crystal structure of a fourth compound, [La(hfa)(3)(H2O)Cu(salen)] (4), has been determined at -100 degrees C; hfa = hexafluoroacetylacetonato, salen N,N'-ethyle nebis(salicylideneaminato), and Meim = 1-methylimidazole. [La(hfa)(3)N i(salen)] (5), isomorphous with 1, has also been synthesized. 1 crysta llizes in the monoclinic system, space group P2(1)/n, with a 17.292(5) Angstrom, b = 22.370(5) Angstrom, c 19.658(6) Angstrom, beta = 90.07( 2)degrees, and Z = 8. 2 crystallizes in the triclinic system, space gr oup Pi, with a = 12.207(3) Angstrom, b = 13.019() Angstrom, c = 13.011 (6) Angstrom, alpha 82.87(4)degrees, beta = 83.55(3)degrees, gamma = 7 0.91(3)degrees, Z = 2. 3 crystallizes in the monoclinic system, Space group P2(1)/n, with a 16.521(9) A, b = 20.381(5) Angstrom, c 12.758(6) Angstrom, beta = 93.22(6)degrees, and Z = 4. 4 crystallizes in the mo noclinic system, space group P2(1)/1, with a 12.826(2) Angstrom, b = 2 3.067(8) Angstrom, c = 13.081(3) Angstrom, beta 91.37(2)degrees, and Z = 4. The structures of 1, 2, and 4 consist of dimers of binuclear uni ts in which the metal ions are bridged by the oxygen atoms of the sale n ligand, with rather short Cu-Cu intermolecular separations (3.630(3) Angstrom for 1, 4.251(2) Angstrom for 2, and 3.620(2) Angstrom for 4) . The Gd-III ion in 1 and the Y-III ion in 2 have a square antiprismat ic environment, while the La-III ion in 4 is nine-coordinate with a wa ter molecule in the La-III coordination polyhedron. In compounds 1, 2, and 4 the CUII ion has a square planar environment. The Gd-Cu distanc es are 3.198(2) and 3.231(2) Angstrom for 1, the Y-Cu distance is 3.25 7(1) Angstrom for 2, and the La-Cu distance is 3.381(2) Angstrom 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 inve stigated. They have revealed Gd-III-Cu-II ferromagnetic interactions. The ground state of 3 is an S = 4 state, stabilized by 5.68 cm(-1) wit h respect to the S = 3 excited state. The situation is more complicate d for 1, due to the presence of Cu-Cu intermolecular interactions.