Single Molecule Magnet Behavior of a Pentanuclear Mn-Based Metallacrown Complex: Solid State and Solution Magnetic Studies

The magnetic behavior of the pentanuclear complex of formula Mn II (O 2 CCH 3 ) 2 [12-MC Mn III (N)shi -4](DMF) 6, 1, was investigated using magnetization and magnetic susceptibility measurements both in the solid state and in solution. Complex 1 has a nearly planar structure, made of a central Mn II ion surrounded by four peripheral Mn III ions. Solid state variable-field dc magnetic susceptibility experiments demonstrate that 1 possesses a low value for the total spin in the ground state; fitting appropriate expressions to the data results in antiferromangetic coupling both between the peripheral Mn III ions ( J = −6.3 cm –1 ) and between the central Mn II ion and the Mn III ones ( J ′ = −4.2 cm –1 ). In order to obtain a reasonable fit, a relatively large single ion magnetic anisotropy ( D ) value of 1 cm –1 was necessary for the central Mn II ion. The single crystal magnetization measurements using a microsquid array display a very slight opening of the hysteresis loop but only at a very low temperature (0.04 K), which is in line with the ac susceptibility data where a slow relaxation of the magnetization occurs just around 2 K. In frozen solution, complex 1 displays a frequency dependent ac magnetic susceptibility signal with an energy barrier to magnetization reorientation ( E ) and relaxation time at an infinite temperature (τ o ) of 14.7 cm –1 and 1.4 × 10 –7 s, respectively, demonstrating the single molecule magnetic behavior in solution.