Shultz David A, Vostrikova Kira E, Bodnar Scot H, Koo Hyun-Joo, Whangbo Myung-Hwan, Kirk Martin L, Depperman Ezra C, Kampf Jeff W
Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, USA.
J Am Chem Soc. 2003 Feb 12;125(6):1607-17. doi: 10.1021/ja020715x.
We report molecular structures and temperature-dependent magnetic susceptibility data for several new metal complexes of heterospin triplet ground-state biradical ligands. The ligands are comprised of both nitronyl-nitroxide (NN) and semiquinone (SQ) spin carriers. Five compounds are five-coordinate M(II) complexes (M = Mn, Co, Ni, Cu, and Zn), and one is a six-coordinate Ni(II) complex. Five compounds were structurally characterized. During copper complex formation a reaction with methanol occurs to form a unique methoxy-substituted SQ ring. Variable-temperature magnetic susceptibility studies are consistent with strong intraligand (NN-SQ and NN-PhSQ) ferromagnetic exchange coupling. For the five-coordinate Mn, Co, and Ni complexes, the S = 1 ligand is antiferromagnetically coupled to the metal. For both the five-coordinate Cu complex and the six-coordinate Ni complex, the ligand is ferromagnetically coupled to the metal spins in accordance with orbital symmetry arguments. Despite the low molecular symmetries, the predicted trend in metal-ligand exchange interactions is supported by spin dimer analysis based on extended Hückel calculations. For (NN-SQ)NiTp(Cum,Me)() (Tp(Cum,Me)() = hydro-tris(3-cumenyl-5-methylpyrazolyl)borate), an antisymmetric exchange term was required for the best fit of the magnetic susceptibility data. Antisymmetric exchange was less important for the other complexes due to inherently smaller Deltag. Finally, it is shown that intraligand exchange coupling is of paramount importance in stabilizing high-spin states of mixed metal-biradical complexes.
我们报告了几种具有异自旋三重态基态双自由基配体的新型金属配合物的分子结构和温度依赖性磁化率数据。这些配体由硝酰基氮氧化物（NN）和半醌（SQ）自旋载体组成。五个化合物是五配位的M（II）配合物（M = Mn、Co、Ni、Cu和Zn），一个是六配位的Ni（II）配合物。对五个化合物进行了结构表征。在铜配合物形成过程中，会与甲醇发生反应，形成独特的甲氧基取代的SQ环。变温磁化率研究与强的配体内（NN - SQ和NN - PhSQ）铁磁交换耦合一致。对于五配位的Mn、Co和Ni配合物，S = 1的配体与金属反铁磁耦合。对于五配位的Cu配合物和六配位的Ni配合物，根据轨道对称理论，配体与金属自旋铁磁耦合。尽管分子对称性较低，但基于扩展休克尔计算的自旋二聚体分析支持了金属 - 配体交换相互作用的预测趋势。对于（NN - SQ）NiTp（Cum，Me）（）（Tp（Cum，Me）（） = 氢 - 三（3 - 异丙基 - 5 - 甲基吡唑基）硼酸酯），为了最佳拟合磁化率数据，需要一个反对称交换项。由于固有地较小的Δg，反对称交换对其他配合物不太重要。最后，结果表明配体内交换耦合对于稳定混合金属 - 双自由基配合物的高自旋态至关重要。
