Dunstan Maja A, Brown Dominic S, Sorace Lorenzo, Mole Richard A, Boskovic Colette
School of Chemistry, The University of Melbourne, Parkville, VIC, 3010, Australia.
Department of Chemistry, "Ugo Schiff", Universita Degli Studi Firenze, Via della Lastruccia, 13, 50019, Sesto Fiorentino, Italy.
Chem Asian J. 2022 Jul 15;17(14):e202200325. doi: 10.1002/asia.202200325. Epub 2022 Jun 20.
Incorporating lanthanoid(III)-radical magnetic exchange coupling is a possible route to improving the performance of lanthanoid (Ln) single-molecule magnets (SMMs), molecular materials that exhibit slow relaxation and low temperature quantum tunnelling of the magnetization. Complexes of Gd(III) can conveniently be used as model systems to study the Ln-radical exchange coupling, thanks to the absence of the orbital angular momentum that is present for many Ln(III) ions. Two new Gd(III)-radical compounds of formula [Gd(18-c-6)X SQ(NO )].I (18-c-6=18-crown-6, X SQ⋅ =tetrahalo-1,2-semiquinonate, 1: X=Cl, 2: X=Br) have been synthesized, and the presence of the dioxolene ligand in its semiquinonate form confirmed by X-ray crystallography, UV-Visible-NIR spectroscopy and voltammetry. Static magnetometry and EPR spectroscopy indicate differences in the low temperature magnetic properties of the two compounds, with antiferromagnetic exchange coupling of J ∼-2.0 cm (H =-2J (S S )) determined by data fitting. Interestingly, compound 1 exhibits slow magnetic relaxation in applied magnetic fields while 2 relaxes much faster, pointing to the major role of packing effects in modulating slow relaxation of the magnetization.
引入镧系元素（III）-自由基磁交换耦合是提高镧系元素（Ln）单分子磁体（SMM）性能的一条可能途径，Ln单分子磁体是一类表现出磁化强度缓慢弛豫和低温量子隧穿的分子材料。由于许多Ln（III）离子存在轨道角动量，而Gd（III）配合物不存在该轨道角动量，因此Gd（III）配合物可方便地用作研究Ln-自由基交换耦合的模型体系。已合成了两种新的化学式为[Gd(18-c-6)X SQ(NO )].I的Gd（III）-自由基化合物（18-c-6 = 18-冠-6，X SQ⋅ = 四卤代-1,2-半醌，1：X = Cl，2：X = Br），并通过X射线晶体学、紫外-可见-近红外光谱和伏安法证实了半醌形式的二氧戊环配体的存在。静态磁强计和电子顺磁共振光谱表明这两种化合物在低温磁性能上存在差异，通过数据拟合确定反铁磁交换耦合常数J ∼ -2.0 cm （H = -2J (S S )）。有趣的是，化合物1在施加磁场时表现出缓慢的磁弛豫，而化合物2弛豫得快得多，这表明堆积效应在调节磁化强度的缓慢弛豫中起主要作用。
