Hybrid Organic/Inorganic Molecular Materials Formed by Tetrathiafulvalene Radicals and Magnetic Trimeric Clusters of Dimetallic Oxalate-Bridged Complexes: The Series (TTF)_4{M~(II)(H_2O)_2[M~(II)(ox)_3]_2}·nH_2O (M~(II) = Mn, Fe, Co, Ni, Cu and Zn;

摘要

The first examples of trimeric, dimetallic, pure oxalatebridged complexes [ox = (C_2O_4)~(2-)] have been synthesized and characterized structurally and magnetically for the two new series of crystalline molecular assemblies formulated as (TTF)_4{M~(II)(H_2O)_2[M~(II)(ox)_3]_2}·nH_2O [for M~(III) = Cr M~(II) = Mn (1), Fe (2), Co (3), Ni(4), Cu(5) and Zn (6); for M~(III) = Fe; M~(II) = Mn(7), Fe (8), Co (9), Ni (10) and Zn (11)]. Both series (Cr_2M and Fe_2M) are isostructural. The crystal structure of (TTF)_4(Mn(H_2O)_2]Cr(ox)_3]_2}14H_2O (1) [monoclinic, space group C2/c (no. 15), a = 13.240(5) A, b = 19.450(5) A, c = 27.690(5) A, β = 97.63(5)°, V = 7068(3) A~3 and Z = 4] shows alternating layers of the organic radical TTF, arranged in an unprecedented one-dimensional k-type phase formed by parallel chains of orthogonal dimers along the a axis, and layers of centrosymmetrical Cr-Mn-Cr trimers with oxalate bridges. The magnetic measurements show ferromagnetic coupling within the trimers for the Cr_2M series and antiferromagnetic for the Fe_2M series, giving rise to high-spin molecules in both cases [S = 11/2, 10/2, 9/2, 8/2 and 7/2 in compounds (1-5), respectively, and S = 5/2, 6/2, 7/2 and 8/2 in compounds (7-10), respectively]. These high-spin ground states are confirmed by magnetization measurements at 2 K. The ESR spectra of all compounds confirm the presence of the metals and a small amount of isolated TTF radical in all the samples, which is typical for these kinds of radical salts.