Spectroscopic and Magnetic Studies of Co(II) Scorpionate Complexes: Is There a Halide Effect on Magnetic Anisotropy?
Spectroscopic and Magnetic Studies of Co(II) Scorpionate Complexes: Is There a Halide Effect on Magnetic Anisotropy?
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DOI：
10.1021/acs.inorgchem.2c04468
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发表时间：
2023-03-31
影响因子：
4.6
通讯作者：
Fiedler, Adam T.
中科院分区：
文献类型：
--
作者：
Devkota, Laxmi;SantaLucia, Daniel J.;Fiedler, Adam T.
过渡金属配合物的单分子磁性的观察依赖于零场分裂（zero-field splitting，简称ZMF）现象，它是由自旋轨道耦合（spin-orbit coupling，SOC）与配体场诱导的对称性降低相互作用而产生的。先前的研究已经表明，与3d金属离子配合物的大小，有时通过与具有大的自由原子SOC常数的重卤化物配体（Br和I）的配位增强。在这项研究中，我们系统地探测这种“重原子效应”的高自旋钴（II）卤化物配合物支持取代的氢三（吡唑-1-基）硼酸酯配体（Tp（tBu，Me）和Tp（Ph，Me））。制备了两个系列的配合物：[（考克斯）-X-II（Tp（tBu，Me））]（1-X; X = F，Cl，Br，and I）和[（考克斯）-X-II（Tp（Ph，Me））（Hpz（Ph，Me））]（2-X; X = Cl，Br，and I），其中Hpz（Ph，Me）为单齿吡唑配体。检查与直流磁力，高频和场电子顺磁共振，远红外磁光谱产生的轴向（D）和菱形（E）每个复杂的磁参数。除1-F外，四配位1-X系列的配合物在10和13 cm（-1）之间显示出正的D值，与卤化物尺寸无关。五坐标2-X系列在-60和-90 cm（-1）之间表现出大的负D值。借助配位场理论和从头计算解释的磁性参数阐明了分子几何形状，配位场效应，和金属配位体的共价性在控制钴卤化物配合物的磁共振的大小的作用。
The observation of single-molecule magnetism in transition-metal complexes relies on the phenomenon of zero-field splitting (ZFS), which arises from the interplay of spin-orbit coupling (SOC) with ligand-field-induced symmetry lowering. Previous studies have demonstrated that the magnitude of ZFS in complexes with 3d metal ions is sometimes enhanced through coordination with heavy halide ligands (Br and I) that possess large free-atom SOC constants. In this study, we systematically probe this "heavy-atom effect" in high-spin cobalt(II)-halide complexes supported by substituted hydrotris(pyrazol-1-yl)borate ligands (Tp(tBu,Me )and Tp(Ph,Me)). Two series of complexes were prepared: [(CoX)-X-II(Tp(tBu,Me))] (1-X; X = F, Cl, Br, and I) and [(CoX)-X-II(Tp(Ph,Me))(Hpz(Ph,Me))] (2-X; X = Cl, Br, and I), where Hpz(Ph,Me) is a monodentate pyrazole ligand. Examination with dc magnetometry, high-frequency and-field electron paramagnetic resonance, and far-infrared magnetic spectroscopy yielded axial (D) and rhombic (E) ZFS parameters for each complex. With the exception of 1-F, complexes in the four-coordinate 1-X series exhibit positive D-values between 10 and 13 cm(-1), with no dependence on halide size. The five-coordinate 2-X series exhibit large and negative D-values between -60 and -90 cm(-1). Interpretation of the magnetic parameters with the aid of ligand-field theory and ab initio calculations elucidated the roles of molecular geometry, ligand-field effects, and metal-ligand covalency in controlling the magnitude of ZFS in cobalt-halide complexes.