Ghatak Aheli, Bhatt Gargi, Rana Rajanikanta, Gupta Sandeep K, Meyer Franc, Rajaraman Gopalan, Murugavel Ramaswamy
Department of Chemistry, Indian Institute of Technology, Bombay, Powai, 400076, Mumbai, India.
Department of Chemistry, Indian Institute of Technology, Delhi, Hauz Khas, 110016, New Delhi, India.
Chem Asian J. 2025 Mar 17;20(6):e202401477. doi: 10.1002/asia.202401477. Epub 2025 Jan 22.
Isostructural Dy(III) and Er(III) complexes [L Ln(HO)][I] ⋅ L ⋅ (CHCl) (Ln=Dy (1), Er (3)) and [L Ln(HO)][I] ⋅ L ⋅ (CHCl) (Ln=Dy (2), Er (4)), with distorted pentagonal bipyramidal geometry (D) around the central metal were synthesized by utilizing two bulky phosphonamide ligands, adamantyl phosphonamide, (Ad)P(O)(NHPr) (L) and carbazolyl phosphoramide (Cz)P(O)(NHPr) (L). The resultant complexes were investigated for their magnetic properties in order to elucidate the impact of modification of the coordinating P-O bond environment either by increasing steric bulk and/or introduction of a third P-N bond at the central phosphorus atom. Magnetic studies revealed substantial energy barriers (U) of 640 K and 491 K for Dy compounds 1 and 2, respectively, rendering them as some of the best-performing air-stable SIMs amongst the class of SIMs with D symmetry. Compounds 1 and 2 exhibit magnetization blocking (T) at 6.5 K and 6 K, respectively, at a sweep rate of 20 Oe/s. Compound 1 benefits from increased lattice intermetallic distances due to bulky adamantyl substituent, but exhibits a significant deviation from linear axial (P)O-Dy-O(P) geometry (173.7(1)°). In addition to the deviation from linearity, the incorporation of a bulky adamantane (or carbazole) ligand in complex 1 (or 2) was found to result in relatively strong Dy…H-C agostic interactions, with distances of 3.698 Å (3.376 Å). These interactions are expected to induce transverse anisotropy. Ab initio CASSCF/RASSI-SO/SINGLE_ANISO calculations offer valuable insights into the dynamics of magnetic relaxation and the impact of axial bulkiness on the anisotropy of D systems. Beyond highlighting the crucial role of crystal field and symmetry in achieving high-temperature SIMs, this study also explores how the secondary coordination sphere can be engineered to create novel SIMs.
利用两个大体积膦酰胺配体，即金刚烷基膦酰胺（Ad）P(O)(NHPr)（L¹）和咔唑基磷酰胺（Cz）P(O)(NHPr)（L²），合成了具有围绕中心金属的扭曲五角双锥几何构型（D₃ₕ）的同构Dy(III)和Er(III)配合物[L¹Ln(OH₂)][I]⋅L²⋅(CHCl₃)（Ln = Dy (1)，Er (3)）以及[L²Ln(OH₂)][I]⋅L¹⋅(CHCl₃)（Ln = Dy (2)，Er (4)）。对所得配合物的磁性进行了研究，以阐明通过增加空间位阻和/或在中心磷原子处引入第三个P-N键来改变配位P-O键环境的影响。磁性研究表明，Dy化合物1和2的能垒（Ueff）分别高达640 K和491 K，使其成为具有D₃ₕ对称性的单分子磁体（SIMs）中性能最佳的空气稳定型SIMs之一。化合物1和2在扫描速率为20 Oe/s时，分别在6.5 K和6 K表现出磁化阻挡（Tb）。化合物1因大体积金刚烷基取代基而使晶格金属间距离增加，但呈现出与线性轴向（P）O-Dy-O（P）几何构型的显著偏差（173.7(1)°）。除了线性偏差外，在配合物1（或2）中引入大体积金刚烷（或咔唑）配体还导致相对较强的Dy…H-C次级相互作用，距离为3.698 Å（3.376 Å）。这些相互作用预计会诱导横向各向异性。从头算CASSCF/RASSI-SO/SINGLE_ANISO计算为磁弛豫动力学以及轴向空间位阻对D₃ₕ体系各向异性的影响提供了有价值的见解。除了强调晶体场和对称性在实现高温SIMs中的关键作用外，本研究还探索了如何设计第二配位层以创造新型SIMs。
