Synthesis, Spectroscopic Characterization, and Determination of the Solution Association Energy of the Dimer [Co{N(SiMe3)2}2]2: Magnetic Studies of Low-Coordinate Co(II) Silylamides [Co{N(SiMe3)2}2L] (L = PMe3, Pyridine, and THF) and Related Species That Reveal Evidence of Very Large Zero-Field Splittings
Synthesis, Spectroscopic Characterization, and Determination of the Solution Association Energy of the Dimer [Co{N(SiMe3)2}2]2: Magnetic Studies of Low-Coordinate Co(II) Silylamides [Co{N(SiMe3)2}2L] (L = PMe3, Pyridine, and THF) and Related Species That Reveal Evidence of Very Large Zero-Field Splittings
复制标题
DOI：
10.1021/ic402019w
复制
发表时间：
2013-10-21
影响因子：
4.6
通讯作者：
Power, Philip P.
中科院分区：
文献类型：
--
作者：
Bryan, Aimee M.;Long, Gary J.;Power, Philip P.
合成了有用的二聚钴（II）硅酰胺配合物[Co{N（SiMe 3）（2）}（2）]（2）（1）及其几种刘易斯碱配合物，研究了它们的合成、磁性和光谱性质。变温核磁共振（NMR）结果表明，1在苯溶液中处于单体-二聚体平衡，300 K时的缔合能为-0.30（20）kcal mol（-1）.多晶红棕色[Co{N（SiMe 3）（2）}（2）]（2）（1）的磁性数据表明，它在两个S = 3/2的钴（II）中心之间显示出强的反铁磁交换耦合，表示为-2J（ex）S（1）S（2），J（ex）值为-215（5）cm（-1），这与其固态的桥接二聚体结构一致。首次报道了1在溶液中的电子光谱，表明单体“Co{N（SiMe 3）（2）}（2）”的熔点、合成、电子光谱和磁性研究与亮绿色四氢呋喃（THF）配合物[Co{N（SiMe 3）（2）}（2）（THF）]（4）的结果一致。用不同的刘易斯碱处理1，得到单体三配位物种[Co{N（SiMe 3）（2）}（2）（PMe 3）]（2）和[Co{N（SiMe 3）（2）}（2）（THF）]（4），以及先前报道的[Co{N（SiMe 3）（2）}（2）（py）]（3）-和四配位物种[Co{N（SiMe 3）（2）}（2）（py）（2）]（5），产率良好.顺磁性配合物2-4，其特征在于通过电子和H-1 NMR光谱，并通过X-射线晶体学的情况下，2和4。2-5和已知的三配位钴（II）物种的磁性研究[Na（12-冠-4）（2）] [Co{N（SiMe 3）（2）}（3）]（6）表明它们具有相当大的χ T-M积，因此具有磁矩，比仅自旋的值1.875 emu K mol（-1）和3.87 mu（B）更高，这表明由伪三角晶场引起的显著的零场分裂和g张量各向异性。2-6的chi T-M拟合产生大的g张量各向异性、大的负D值（在-62 cm（-1）和-82 cm（-1）之间）和在+/- 10 cm（-1）和+/- 21 cm（-1）之间的E值。
The synthesis, magnetic, and spectroscopic characteristics of the synthetically useful dimeric cobalt(II) silylamide complex [Co{N(SiMe3)(2)}(2)](2) (1) and several of its Lewis base complexes have been investigated. Variable-temperature nuclear magnetic resonance (NMR) spectroscopy of 1 showed that it exists in a monomer-dimer equilibrium in benzene solution and has an association energy (Delta G(reacn)) of -0.30(20) kcal mol(-1) at 300 K. Magnetic data for the polycrystalline, red-brown [Co{N(SiMe3)(2)}(2)](2) (1) showed that it displays strong antiferromagnetic exchange coupling, expressed as -2J(ex)S(1)S(2), between the two S = 3/2 cobalt(II) centers with a J(ex) value of -215(5) cm(-1), which is consistent with its bridged dimeric structure in the solid state. The electronic spectrum of 1 in solution is reported for the first time, and it is shown that earlier reports of the melting point, synthesis, electronic spectrum, and magnetic studies of the monomer "Co{N(SiMe3)(2)}(2)" are consistent with those of the bright green-colored tetrahydrofuran (THF) complex [Co{N(SiMe3)(2)}(2)(THF)] (4). Treatment of 1 with various Lewis bases yielded monomeric three-coordinated species-[Co{N(SiMe3)(2)}(2)(PMe3)] (2), and [Co{N(SiMe3)(2)}(2)(THF)] (4), as well as the previously reported [Co{N(SiMe3)(2)}(2)(py)] (3)-and the four-coordinated species [Co{N(SiMe3)(2)}(2)(py)(2)] (5) in good yields. The paramagnetic complexes 2-4 were characterized by electronic and H-1 NMR spectroscopy, and by X-ray crystallography in the case of 2 and 4. Magnetic studies of 2-5 and of the known three-coordinated cobalt(II) species [Na(12-crown-4)(2)] [Co{N(SiMe3)(2)}(3)] (6) showed that they have considerably larger chi T-M products and, hence, magnetic moments, than the spin-only values of 1.875 emu K mol(-1) and 3.87 mu(B) which is indicative of a significant zero-field splitting and g-tensor anisotropy resulting from the pseudo-trigonal crystal field. A fit of chi T-M for 2-6 yields a large g-tensor anisotropy, large negative D-values (between -62 cm(-1) and -82 cm(-1)), and E-values between +/- 10 cm(-1) and +/- 21 cm(-1).