Structural, magnetic, redox and theoretical characterization of seven-coordinate first-row transition metal complexes with a macrocyclic ligand containing two benzimidazolyl N-pendant arms,Dalton Transactions

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Structural, magnetic, redox and theoretical characterization of seven-coordinate first-row transition metal complexes with a macrocyclic ligand containing two benzimidazolyl N-pendant arms
Dalton Transactions ( IF 3.5 ) Pub Date : 2020/03/16 , DOI: 10.1039/d0dt00166j
Bohuslav Drahoš _{1,

2,

3,

4,

5} , Ivana Císařová _{1,

2,

5,

6,

7} , Oleksii Laguta _{5,

8,

9} , Vinicius T. Santana _{5,

8,

9} , Petr Neugebauer _{5,

8,

9} , Radovan Herchel _{1,

2,

3,

4,

5}

Affiliation

A structurally new heptadentate derivative of a 15-membered pyridine-based macrocycle containing two benzimidazol-2-yl-methyl N-pendant arms (L = 3,12-bis((1H-benzimidazol-2-yl)methyl)-6,9-dioxa-3,12,18-triazabicyclo[12.3.1]octadeca-1(18),14,16-triene) was synthesized and its complexes with the general formula [M(L)](ClO₄)₂·1.5CH₃NO₂ (M = Mn^II (1), Fe^II (2), Co^II (3) and Ni^II (4)) were thoroughly investigated. X-ray crystal structures confirmed that all complexes are seven-coordinate with axially compressed pentagonal bipyramidal geometry having the largest distortion for Ni^II complex 4. Fe^II, Co^II and Ni^II complexes 2, 3 and 4 show rather large magnetic anisotropy manifested by moderate to high obtained values of the axial zero-field splitting parameter D (7.9, 40.3, and −17.2 cm⁻¹, respectively). Magneto-structural correlation of the Fe^II, Co^II and Ni^II complexes with L and with previously studied structurally similar ligands revealed a significant impact of the functional group in pendant arms on the magnetic anisotropy especially that of the Co^II and Ni^II complexes and some recommendations concerning the ligand-field design important for anisotropy tuning in future. Furthermore, complex 3 showed field-induced single-molecule magnet behavior described with the Raman (C = 507 K⁻ⁿ s⁻¹ for n = 2.58) relaxation process. The magnetic properties of the studied complexes were supported by theoretical calculations, which very well correspond with the experimental data of magnetic anisotropy. Electrochemical measurements revealed high positive redox potentials for M^3+/2+ couples and high negative redox potentials for M^2+/+ couples, which indicate the stabilization of the oxidation state +II expected for the σ-donor/π-acceptor ability of benzimidazole functional groups.

中文翻译：

带有两个苯并咪唑基N悬臂的大环配体的七坐标首行过渡金属配合物的结构，磁性，氧化还原和理论表征

15元吡啶基大环的结构新的七齿衍生物，其中包含两个苯并咪唑-2-基-甲基N-侧链（L = 3,12-双（（1 H-苯并咪唑-2-基）甲基）-6合成了9,9-二恶英-3,12,18-三氮杂双环[12.3.1] octadeca-1（18），14,16-三烯）及其配合物，通式为[M（L）]（ClO ₄）₂ ·1.5CH ₃ NO ₂（M = Mn ^II（1），Fe ^II（2），Co ^II（3）和Ni ^II（4））进行了彻底的调查。X射线晶体结构证实，所有配合物均为7坐标，且轴向压缩的五边形双锥体几何形状对Ni ^II配合物4具有最大的畸变。铁^II，钴^II和Ni ^II络合物2，3和4由中等表现高所获得的轴向零场分裂参数的值显示相当大的磁各向异性d（7.9，40.3，和-17.2厘米^-1分别）。Fe ^II，Co ^II和Ni ^II配合物与L和先前研究的结构相似的配体揭示了悬臂上的官能团对磁各向异性的重要影响，特别是Co ^II和Ni ^II配合物的磁影响以及有关配体场设计的一些建议对将来的各向异性调谐很重要。此外，配合物3表现出用拉曼描述的场感应单分子磁体行为（对于n，C = 507 K ^{- n} s ^-1= 2.58）松弛过程。理论计算支持了所研究的配合物的磁性，这与磁各向异性的实验数据非常吻合。电化学测量显示，M ^{3 + / 2 +对}具有高正氧化还原电势，M ^{2 + / +}对具有高负氧化还原电势，表明氧化态+ II的σ-供体/π-受体能力预期稳定。苯并咪唑官能团。

更新日期：2020-04-08

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