Combined Experimental and Ab Initio Methods for Rationalization of Magneto-Luminescent Properties of Yb^III Nanomagnets Embedded in Cyanido/Thiocyanidometallate-Based Crystals

The ab initio calculations were correlated with magnetic and emission characteristics to understand the modulation of properties of NIR-emissive [YbIII(2,2′-bipyridine-1,1′-dioxide)4]3+ single-molecule magnets by cyanido/thiocyanidometallate counterions, [AgI(CN)2]− (1), [AuI(SCN)2]− (2), [CdII(CN)4]2–/[CdII2(CN)7]3– (3), and [MIII(CN)6]3– [MIII = Co (4), Ir (5), Fe (6), Cr (7)]. Theoretical studies indicate easy-axis-type ground doublets for all YbIII centers. They differ in the magnetic axiality; however, transversal g-tensor components are always large enough to explain the lack of zero-dc-field relaxation. The excited doublets lie more than 120 cm–1 above the ground one for all YbIII centers. It was confirmed by high-resolution emission spectra reproduced from the ab initio calculations that give reliable insight into energies and oscillator strengths of optical transitions. These findings indicate the dominance of Raman relaxation with the power n varying from 2.93(4) to 6.9(2) in the 4–3–5–1–2 series. This trend partially follows the magnetic axiality, being deeper correlated with the phonon modes schemes of (thio)­cyanido matrices.本研究将从头算（ab initio calculation）与磁学及发射光谱特性相关联，以阐明氰根/硫氰根金属盐抗衡离子对近红外发射（near-infrared emissive, NIR）的[YbIII(2,2′-联吡啶-1,1′-二氧化物)4]3+单分子磁体（single-molecule magnets, SMMs）性能的调控机制。所采用的抗衡离子包括：[AgI(CN)2]−（标记为1）、[AuI(SCN)2]−（标记为2）、[CdII(CN)4]2–/[CdII2(CN)7]3–（标记为3）以及[MIII(CN)6]3–[MIII = Co(4)、Ir(5)、Fe(6)、Cr(7)]。理论研究显示，所有三价镱（YbIII）中心均存在易轴型基态二重态；各体系的磁轴向性存在差异，但横向g张量分量始终足够大，可合理解释零直流场弛豫现象的缺失。对于所有YbIII中心，其激发态二重态的能级均比基态二重态高出120 cm–1以上。通过从头算重现的高分辨发射光谱证实了上述结论，该光谱可为光学跃迁的能级与振子强度提供可靠的理论依据。研究结果表明，在4–3–5–1–2系列样品中，拉曼弛豫（Raman relaxation）占据主导地位，其幂指数n介于2.93(4)至6.9(2)之间。该变化趋势一定程度上契合磁轴向性的演化规律，且与（硫）氰根基质的声子模式分布具有更紧密的相关性。