Mn₁₂ -Acetate Complexes Studied as Single Molecules

The phenomenon of single molecule magnet (SMM) behavior of mixed valent Mn₁₂ coordination clusters of general formula [Mn^III ₈ Mn^IV ₄ O₁₂ (RCOO)₁₆ (H₂ O)₄ ] had been exemplified by bulk samples of the archetypal [Mn^III ₈ Mn^IV ₄ O₁₂ (CH₃ COO)₁₆ (H₂ O)₄ ] (4) molecule, and the molecular origin of the observed magnetic behavior has found support from extensive studies on the Mn₁₂ system within crystalline material or on molecules attached to a variety of surfaces. Here we report the magnetic signature of the isolated cationic species [Mn₁₂ O₁₂ (CH₃ COO)₁₅ (CH₃ CN)]⁺ (1) by gas phase X-ray Magnetic Circular Dichroism (XMCD) spectroscopy, and we find it closely resembling that of the corresponding bulk samples. Furthermore, we report broken symmetry DFT calculations of spin densities and single ion tensors of the isolated, optimized complexes [Mn₁₂ O₁₂ (CH₃ COO)₁₅ (CH₃ CN)]⁺ (1), [Mn₁₂ O₁₂ (CH₃ COO)₁₆ ] (2), [Mn₁₂ O₁₂ (CH₃ COO)₁₆ (H₂ O)₄ ] (3), and the complex in bulk geometry [Mn^III ₈ Mn^IV ₄ O₁₂ (CH₃ COO)₁₆ (H₂ O)₄ ] (5). The found magnetic fingerprints - experiment and theory alike - are of a remarkable robustness: The Mn^IV ₄ core bears almost no magnetic anisotropy while the surrounding Mn^III ₈ ring is highly anisotropic. These signatures are truly intrinsic properties of the Mn₁₂ core scaffold within all of these complexes and largely void of the environment. This likely holds irrespective of bulk packing effects.