X‑ray Magnetic Circular Dichroism (XMCD) Study of a Methoxide-Bridged DyIII–CrIII Cluster Obtained by Fluoride Abstraction from cis-[CrIIIF2(phen)2]+

An isostructural series of dinuclear chromium­(III)–lanthanide­(III) clusters is formed by fluoride abstraction of cis-[CrF2(phen)2]+ by Ln3+ resulting in LnF3 and methoxide-bridged Cr–Ln clusters (Ln = Nd (1), Tb (2), Dy (3)) of formula [CrIII(phen)2(μ-MeO)2Ln­(NO3)4xMeOH (x = 2–2.73). In contrast to fluoride, methoxide bridges in a nonlinear fashion, which facilitates chelation. For 3, X-ray magnetic circular dichroism (XMCD) provides element-specific magnetization curves that are compared to cluster magnetization and susceptibility data acquired by SQUID magnetometry. The combination of XMCD and SQUID is able to resolve very small magnetic coupling values and reveals a weak CrIII–DyIII coupling of j = −0.04(3) cm–1. The DyIII ion has a ground-state Kramers doublet of mJ = ±13/2, and the first excited doublet is found to be mJ = ±11/2 at an energy of δ = 57(21) cm–1. The CrIII ion exhibits a uniaxial anisotropy of DCr = −1.7(1.0) cm–1. Further, we observe that a weak anisotropic coupling of dipolar origin is sufficient to model the data, suggesting that methoxide bridges do not play a significant role in the magnetic coupling for the present systems.