Chemistry Department, University of Ottawa , 10 Marie Curie, Ottawa, ON, K1N6N5, Canada.
J Am Chem Soc. 2013 Sep 11;135(36):13242-5. doi: 10.1021/ja404846s. Epub 2013 Aug 27.
The effect of electron-withdrawing ligands on the energy barriers of Single-Molecule Magnets (SMMs) is investigated. By introducing highly electron-withdrawing atoms on targeted ligands, the energy barrier was significantly enhanced. The structural and magnetic properties of five novel SMMs based on a dinuclear {Dy2} phenoxo-bridged motif are explored and compared with a previously studied {Dy2} SMM (1). All complexes share the formula [Dy2(valdien)2(L)2]·solvent, where H2valdien = N1,N3-bis(3-methoxysalicylidene) diethylenetriamine, the terminal ligand L = NO3(-) (1), CH3COO(-) (2), ClCH2COO(-) (3), Cl2CHCOO(-) (4), CH3COCHCOCH3(-) (5), CF3COCHCOCF3(-) (6), and solvent = 0.5 MeOH (4), 2 CH2Cl2 (5). Systematic increase of the barrier was observed for all complexes with the most drastic increase seen in 6 when the acac ligand of 5 was fluorinated resulting in a 7-fold enhancement of the anisotropic barrier. Ab initio calculations reveal more axial g tensors as well as higher energy first excited Kramers doublets in 4 and 6 leading to higher energy barriers for those complexes.
研究了吸电子配体对单分子磁体（SMMs）能垒的影响。通过在目标配体上引入高吸电子原子，能垒得到显著增强。研究了基于双核{Dy2} phenoxo 桥联基序的五个新型 SMM 的结构和磁性质，并与之前研究的{Dy2} SMM（1）进行了比较。所有配合物的分子式均为[Dy2（valdien）2（L）2]·溶剂，其中 H2valdien = N1，N3-双（3-甲氧基水杨醛）二乙三胺，末端配体 L = NO3（-）（1），CH3COO（-）（2），ClCH2COO（-）（3），Cl2CHCOO（-）（4），CH3COCHCOCH3（-）（5），CF3COCHCOCF3（-）（6），溶剂= 0.5 MeOH（4），2 CH2Cl2（5）。所有配合物的能垒均呈系统性增加，其中 5 的 acac 配体氟化得到 6 时，能垒增加最为明显，增加了 7 倍。从头算计算显示，4 和 6 中的轴向 g 张量更多，第一激发的 Kramers 双重态能量更高，导致这些配合物的能垒更高。
