Alkali Metal Based Triimidosulfite Cages as Versatile Precursors for Single‐Molecule Magnets

Abstract

Based on the potassium [{S(tBuN)2(tBuNH)}2K3(tmeda)‐K3{(HNtBu)(NtBu)2S}2] (1) and sodium precursors [S(tBuN)3(thf)3‐Na3SNa3(thf)3(NtBu)3S] (2), [S(tBuN)3(thf)3Na3{(HNtBu)(NtBu)2S}] (3) and [(tmeda)3S‐{Na3(NtBu)3S}2] (4) the syntheses and magnetic properties of three mixed metal triimidosulfite based alkali‐lanthanide‐metal‐cages [(tBuNH)Dy{K(0.5tmeda)}2{(NtBu)3S}2]n (5) and [ClLn{Na(thf)}2{(NtBu)3S}2] with Ln=Dy (6), Er (7) are reported. The corresponding potassium (1) and sodium (2–4) based cages are characterized through XRD and NMR experiments. Preventing lithium chloride co‐complexation led to a significant increase of SMM performance to previously reported sulfur‐nitrogen ligands. The subsequent DyIII‐complexes 5 and 6 display slow relaxation of magnetization at zero field, with relaxation barriers U=77.0 cm−1 for 5, 512.9 and 316.3 cm−1 for 6, respectively. Significantly, the latter complex 6 also exhibits a butterfly‐shaped hysteresis up to 7 K.

Synthesis and Magnetic Properties of Polyimidosulfur- and Bis(benzoxazolyl)methanide-ligated Complexes

“…[18] A true first-order SOC is observed for a Co II ion in a weak octahedral ligand field with a 4 F free ion ground state term, which splits into a 4 T1g ground state term (Figure 1.2.a). Applying a tetragonal distortion (D4h) results in two states, labeled as 4 A2g and…”

“…𝜏 −1 = 𝐴𝐻 𝑛 1 𝑇 + 𝐶𝑇 𝑛 2 + 𝜏 0 −1 exp (− 𝑈 eff 𝑘 B 𝑇 ) + 𝑄 (1)(2)(3)(4) where T devotes to the specific temperature dependency and 𝐴, 𝐶, 𝜏 0 −1 , and 𝑄 are treated as freeto-fit parameters since their determination is highly challenging. The four contributing terms of the relaxation processes are outlined below in detail.…”

“…Equation (1)(2)(3)(4)(5)(6) combines the free-to-fit parameter 𝐴, the magnetic field 𝐻 and 𝑛 1 = 2 for a non-Kramers ion and 𝑛 1 = 4 for a Kramers ion. One can perform field-dependent measurements to identify the direct process, which usually leads to a decay of the relaxation times 𝜏 −1 for high fields (𝐻).…”

“…𝜏 −1 = 𝑄 (1)(2)(3)(4)(5)(6)(7)(8) QTM is a free-to-fit parameter, it is often excluded from determining the energy barrier, especially for field-induced SMMs, where its impact is usually low. [21] Previous attempts to minimize the QTM contribution to the relaxation of SMMs are presented in chapter 1.5.…”

“…[73] To distinguish between a regular paramagnet and an SMM, one must search for maxima in the outof-phase susceptibility χ''. A paramagnet should not display slow relaxation as χT = χS, which results in a zero value for χ'' according to equation (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11). Further, its χ' value is constant and refers directly to χS as the second part of the equation (1-10) is zero.…”