Single-molecule magnets: preparation and properties of mixed-carboxylate complexes.
Single-molecule magnets: preparation and properties of mixed-carboxylate complexes.
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DOI：
10.1021/ic0104048
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发表时间：
2001-08
影响因子：
4.6
通讯作者：
M. Soler;Pau Artús;K. Folting;J. Huffman;D. N. Hendrickson;George Christou Indiana University;
中科院分区：
文献类型：
--
作者：
M. Soler;Pau Artús;K. Folting;J. Huffman;D. N. Hendrickson;George Christou Indiana University;
报道了制备[Mn（12）O（12）（O（2）CR）（16）（H（2）O）（4）]系列单分子磁体（SMM）的混合羧酸盐形式的方法。通过1：1反应得到了[Mn（12）O（12）（O（2）CCHCl（2））（8）（O（2）CCH（2）Bu（t））（8）（H（2）O）（3）]（5）和[Mn（12）O（12）（O（2）CHCl（2））（8）（O（2）CEt）（8）（H（2）O）（3）]（6）。配合物5.CH（2）Cl（2）.H（2）O晶体属三斜晶系空间群P1，在-165 ℃时，a = 15.762（1），B = 16.246（1），c = 23.822（1）A，α = 103.92（1），β = 104.50（1），γ = 94.23（1）度，Z = 2，V = 5674（2）A（3）。配合物6.CH（2）Cl（2）晶体属三斜晶系空间群P1，在-158 ℃时，a = 13.4635（3），B = 13.5162（3），c = 23.2609（5）A，α = 84.9796（6），β = 89.0063（8），γ = 86.2375（6）度，Z = 2，V = 4207.3（3）A（3）。配合物5和6都含有一个[Mn（12）O（12）]核，轴向是CHCl（2）CO（2-）配体，赤道位置是RCO（2-）配体（R = CH（2）Bu（t）（5）或Et（6））.因此，CHCl（2）CO（2-）优先占据位于Mn（III）Jahn-Teller轴上的位置，这是基于羧酸根基团的相对碱性而合理化的。在2.00-300 K范围内在10.0 kG场中的直流磁化率研究表明大的基态自旋，并且在10.0-70.0 kG场和1.80-4.00 K温度范围内收集的磁化数据的拟合给出S = 10，g = 1.89和D = -0.65 K，对于5，S = 10，g = 1.83，D = -0.60 K。这些值是[Mn（12）O（12）（O（2）CR）（16）（H（2）O）（4）]配合物的典型值。交流磁化率研究显示了单分子磁体在毫秒时间尺度内缓慢弛豫的异相磁化率（chi（M）"）信号特征。从chi（M）"与T数据获得的Arrhenius图分别给出了5和6的有效弛豫势垒（U（eff））为71和72 K。(1)H CD（2）Cl（2）的NMR谱表明，5和6是溶解时存在的主要物种，但有证据表明，通过分子内和/或分子间交换过程，轴向和赤道部位之间存在一些配体分布。
Methods are reported for the preparation of mixed-carboxylate versions of the [Mn(12)O(12)(O(2)CR)(16)(H(2)O)(4)] family of single-molecule magnets (SMMs). [Mn(12)O(12)(O(2)CCHCl(2))(8)(O(2)CCH(2)Bu(t))(8)(H(2)O)(3)] (5) and [Mn(12)O(12)(O(2)CHCl(2))(8)(O(2)CEt)(8)(H(2)O)(3)] (6) have been obtained from the 1:1 reaction of the corresponding homocarboxylate species. Complex 5.CH(2)Cl(2).H(2)O crystallizes in the triclinic space group P1 with, at -165 degrees C, a = 15.762(1), b = 16.246(1), c = 23.822(1) A, alpha = 103.92(1), beta = 104.50(1), gamma = 94.23(1) degrees, Z = 2, and V = 5674(2) A(3). Complex 6.CH(2)Cl(2) crystallizes in the triclinic space group P1 with, at -158 degrees C, a = 13.4635(3), b = 13.5162(3), c = 23.2609(5) A, alpha = 84.9796(6), beta = 89.0063(8), gamma = 86.2375(6) degrees, Z = 2, and V = 4207.3(3) A(3). Complexes 5 and 6 both contain a [Mn(12)O(12)] core with the CHCl(2)CO(2-) ligands ordered in the axial positions and the RCO(2-) ligands (R = CH(2)Bu(t) (5) or Et (6)) in equatorial positions. There is, thus, a preference for the CHCl(2)CO(2-) to occupy the sites lying on the Mn(III) Jahn-Teller axes, and this is rationalized on the basis of the relative basicities of the carboxylate groups. Direct current magnetic susceptibility studies in a 10.0 kG field in the 2.00-300 K range indicate a large ground-state spin, and fitting of magnetization data collected in the 10.0-70.0 kG field and 1.80-4.00 K temperature range gave S = 10, g = 1.89, and D = -0.65 K for 5, and S = 10, g = 1.83, and D = -0.60 K for 6. These values are typical of [Mn(12)O(12)(O(2)CR)(16)(H(2)O)(4)] complexes. Alternating current susceptibility studies show the out-of-phase susceptibility (chi(M)' ') signals characteristic of the slow relaxation in the millisecond time scale of single-molecule magnets. Arrhenius plots obtained from chi(M)' ' versus T data gave effective barriers to relaxation (U(eff)) of 71 and 72 K for 5 and 6, respectively. (1)H NMR spectra in CD(2)Cl(2) show that 5 and 6 are the main species present on dissolution, but there is evidence for some ligand distribution between axial and equatorial sites, by intra- and/or intermolecular exchange processes.