Slavensky Hannah H, Parmar Vijay S, Leiszner Sofie S, Thiel Andreas M, Lassen Helene, Calder Stuart, Kibalin Iurii, Iversen Bo B
Department of Chemistry, Aarhus University Langelandsgade 140 DK-8000 Aarhus C Denmark
Oak Ridge National Laboratory, Neutron Scattering Division Oak Ridge Tennessee 37831 USA.
Chem Sci. 2025 Aug 12. doi: 10.1039/d5sc03103f.
Magnetic anisotropy of the central metal atom is a crucial property of single molecule magnets (SMMs). Small structural changes can alter the magnetic properties, and accurate experimental methods to investigate magnetic anisotropy are therefore critical. Here, we investigate two five-coordinated Co(ii) SMMs, [CoClCltpy] (1) and [CoBrCltpy] (2) (Cltpy = 4'-chloro-2,2':6',2''-terpyridine), through multiple techniques. theoretical calculations performed on the two compounds show that both possess axial magnetic anisotropy with the magnetic easy axis pointing towards one of the terminal halogen atoms. Theoretical calculations on SMMs are typically done on isolated molecular species, and to validate this approximation the magnetic anisotropy was further studied through experimental techniques. EPR measurements confirm an axial anisotropy of 1, and magnetic measurements provide experimental Zero-Field Splitting (ZFS) parameters, showing that the values from theoretical calculations are slightly overestimated. The X-ray electron density determined from 20 K single-crystal synchrotron X-ray diffraction data provides estimated d-orbital populations also suggesting axial magnetic anisotropy in both systems, and furthermore suggesting a more pronounced axiality in 1 compared to 2. This is in good agreement with the results obtained from both magnetic measurements and theoretical calculations. The magnetic anisotropy of 1 is quantified experimentally through polarized powder neutron diffraction the site susceptibility method, confirming an axial magnetic anisotropy of the compound. A slight deviation in the easy axis direction is observed between experimental and theoretical results. This, together with the overestimation of the ZFS parameters from theoretical calculations, shows that experimental investigation of the magnetic anisotropy of SMMs is of high relevance.
中心金属原子的磁各向异性是单分子磁体（SMMs）的一个关键性质。微小的结构变化会改变磁性质，因此研究磁各向异性的精确实验方法至关重要。在此，我们通过多种技术研究了两种五配位的Co(ii) SMMs，[CoClCltpy] (1) 和 [CoBrCltpy] (2)（Cltpy = 4'-氯-2,2':6',2''-三联吡啶）。对这两种化合物进行的理论计算表明，它们都具有轴向磁各向异性，磁易轴指向其中一个末端卤素原子。对SMMs的理论计算通常是在孤立的分子物种上进行的，为了验证这种近似，通过实验技术进一步研究了磁各向异性。电子顺磁共振（EPR）测量证实了1的轴向各向异性，磁测量提供了实验零场分裂（ZFS）参数，表明理论计算值略有高估。从20 K单晶同步辐射X射线衍射数据确定的X射线电子密度提供了估计的d轨道占据情况，也表明两个体系中都存在轴向磁各向异性，而且表明1中的轴向性比2中更明显。这与磁测量和理论计算得到的结果高度一致。通过极化粉末中子衍射的位点磁化率方法对1的磁各向异性进行了实验量化，证实了该化合物的轴向磁各向异性。在实验和理论结果之间观察到易轴方向存在轻微偏差。这与理论计算对ZFS参数的高估一起，表明对SMMs磁各向异性的实验研究具有高度相关性。
