Jürgens O., Vidal-Gancedo J., Rovira C., Wurst K., Sporer C., Bildstein B., Schottenberger H., Jaitner P., Veciana J.
Institut de Ciència de Materials de Barcelona (CSIC), Campus Universitari UAB, 08193 Bellaterra, Spain, and Institut für Allgemeine, Anorganische und Theoretische Chemie, Universität Innsbruck, Innrain 52a, A-6020, Innsbruck, Austria.
Inorg Chem. 1998 Sep 7;37(18):4547-4558. doi: 10.1021/ic980495h.
The capability of metallocene bridges as new organometallic magnetic couplers is evaluated by studying the family of diradicals 2 (M = Fe, Ru) consisting of two purely organic alpha-nitronyl aminoxyl radicals connected by a 1,1'-metallocenylene bridge. Preliminary studies performed with 2-metallocenyl-alpha-nitronyl aminoxyl monoradicals 1 (M = Fe, Ru, Os), as reference compounds, show the presence of a small spin density on the central metal of the metallocenes. This fact makes the metallocene units effective bridges to transmit magnetic interactions by a spin polarization mechanism. The study of the magnetic properties of diradicals 2 in the solid state and in diluted frozen solutions reveals the existence of an intramolecular antiferromagnetic exchange interaction between the radical subunits whose strength is highly dependent on the molecular conformation adopted by the diradical. As shown by crystal data and by ESR measurements, an intramolecular hydrogen bond between the two radical units forces the molecule to adopt a cisoid molecular conformation, which determines that the magnetic interaction occurs by a direct through-space interaction between the two SOMOs of the two radical units along with the classical spin polarization mechanism through the sigma-bonds of the metallocene unit. Lattice constants for both structures are as follows: 1 (M = Fe), C(17)H(21)FeN(2)O(2), a = 7.170(1) Å, b = 10.135(2) Å, c = 10.683(2) Å, alpha = 88.88(3) degrees, beta = 83.42(3) degrees, gamma = 79.75(3) degrees, triclinic, P&onemacr;, Z = 2; 2 (M = Fe), C(24)H(32)FeN(4)O(4), a = 11.848(3) Å, b = 11.785(2) Å, c = 17.728(4) Å, beta = 106.25(2) degrees, monoclinic, P2(1)/n, Z = 4.
通过研究由通过1,1'-亚茂金属撑桥连接的两个纯有机α-硝酰基氨基氧自由基组成的双自由基2（M = Fe，Ru）家族，评估了茂金属桥作为新型有机金属磁耦合器的能力。以2-茂金属基-α-硝酰基氨基氧单自由基1（M = Fe，Ru，Os）作为参考化合物进行的初步研究表明，在茂金属的中心金属上存在小的自旋密度。这一事实使得茂金属单元成为通过自旋极化机制传递磁相互作用的有效桥梁。对双自由基2在固态和稀释冷冻溶液中的磁性研究表明，自由基亚基之间存在分子内反铁磁交换相互作用，其强度高度依赖于双自由基所采用的分子构象。如晶体数据和电子顺磁共振测量所示，两个自由基单元之间的分子内氢键迫使分子采用顺式分子构象，这决定了磁相互作用是通过两个自由基单元中的两个单占据分子轨道之间的直接空间相互作用以及通过茂金属单元的σ键的经典自旋极化机制发生的。两种结构的晶格常数如下：1（M = Fe），C(17)H(21)FeN(2)O(2)，a = 7.170(1) Å，b = 10.135(2) Å，c = 10.683(2) Å，α = 88.88(3)°，β = 83.42(3)°，γ = 79.75(3)°，三斜晶系，P&onemacr;，Z = 2；2（M = Fe），C(24)H(32)FeN(4)O(4)，a = 11.848(3) Å，b = 11.785(2) Å，c = 17.728(4) Å，β = 106.25(2)°，单斜晶系，P2(1)/n，Z = 4。
