Solution and Solid State Properties for Low-Spin Cobalt(II) Dibenzotetramethyltetraaza[14]annulene [(tmtaa)CoII] and the Monopyridine Complex,Inorganic Chemistry

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Solution and Solid State Properties for Low-Spin Cobalt(II) Dibenzotetramethyltetraaza[14]annulene [(tmtaa)CoII] and the Monopyridine Complex
Inorganic Chemistry ( IF 4.3 ) Pub Date : 2019-01-08 00:00:00 , DOI: 10.1021/acs.inorgchem.8b02644
Soumyajit Dey ₁ , Bradford B. Wayland ₁ , Michael J. Zdilla ₁

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The single-crystal X-ray structure of solvent-free (tmtaa)Co^II reveals three different π–π intermacrocyclic interactions between tmtaa units (tmtaa = dibenzotetramethyltetraaza[14]annulene). Pairs of inequivalent (tmtaa)Co^II units in the unit cell link into a one-dimensional π–π stacked array in the solid state. Magnetic susceptibility (χ) studies from 300 to 2 K reveal the effects of intermolecular interactions between (tmtaa)Co^II units in the solid state. The effective magnetic moment per Co^II center is constant at 2.83 μ_B from 300 to 100 K and begins to significantly decrease at lower temperatures. The magnetic data are fit to a singlet (S = 0) ground state with a triplet (S = 1) excited state that is 13 cm^–1 higher in energy (−2J = 13 cm^–1). Toluene solutions of (tmtaa)Co^II have ¹H nuclear magnetic resonance (NMR) paramagnetic shifts, a solution-phase magnetic moment μ_eff (295 K) of 2.1 μ_B, and toluene glass electron paramagnetic resonance spectra that are most consistent with a low-spin (S = ¹/₂) Co^II with the unpaired electron located in the d_yz orbital. Pyridine interacts with (tmtaa)Co^II to form a five-coordinate monopyridine complex in which the unpaired electron is in the d_z² orbital. The five-coordinate complex has been structurally characterized by single-crystal X-ray diffraction, and the equilibrium constant for pyridine binding at 295 K has been evaluated by both electronic and ¹H NMR spectra. Density functional theory computation using the UB3LYP hybrid functional places the unpaired electron for (tmtaa)Co^II in the d_yz orbital and that for the monopyridine complex in the d_z² orbital, consistent with spectroscopic observations.

中文翻译：

低自旋钴（II）二苯并四甲基四氮杂[14]环戊烯[（tmtaa）Co ^II ]和一吡啶配合物的溶液和固态性质

无溶剂（tmtaa）Co ^II的单晶X射线结构揭示了tmtaa单元（tmtaa =二苯并四甲基四氮杂[14]环戊烯）之间的三种不同的π-π大环间相互作用。晶胞中成对的不等价（tmtaa）Co ^II单元对链接成固态的一维π-π堆叠阵列。从300到2 K的磁化率（χ）研究揭示了固态的（tmtaa）Co ^II单元之间的分子间相互作用的影响。每钴的有效磁矩^II中心在2.83μ恒定_乙从300至100 K和开始在较低温度下显著降低。磁数据拟合为单峰（小号= O）基态与三线态（S = 1）激发态，其能量高13 cm ^–1（-2 J = 13 cm ^–1）。（tmtaa）有限公司的甲苯溶液^II具有^1和1 H核磁共振（NMR）的顺磁位移，溶液相磁矩μ _EFF 2.1μ的（295 K）_乙，和甲苯玻璃电子顺磁共振光谱是与最一致低自旋（小号= ¹ / ₂）钴^II与位于d不成对电子_的yz轨道。吡啶与（tmtaa）Co ^II相互作用形成五配位的单吡啶配合物，其中不成对的电子在d _{z ²}轨道上。五坐标配合物已通过单晶X射线衍射进行了结构表征，并已通过电子和¹ H NMR光谱评估了295 K处吡啶结合的平衡常数。使用UB3LYP杂合函数的密度泛函理论计算将（tmtaa）Co ^II的不成对电子置于d _yz轨道，并将单吡啶络合物的不成对电子置于d _{z ²}轨道，与光谱观察一致。

更新日期：2019-01-08

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