Extending the family of reduced [Mn12O12(O2CR)16(H2O)x]n− complexes, and their sensitivity to environmental factors

Abstract

The family of reduced [Mn12O12(O2CR)16(H2O)4]n− (n = 1, 2) single-molecule magnets (SMMs) has been expanded with the synthesis of new members using I− as a stoichiometric one-electron reducing agent of the neutral n = 0 complexes. Electrochemical data, 1H NMR spectra of the [Mn12O12(O2CCH2Cl)16(H2O)3]0,−,2− salts, and the crystal structures of two complexes, (PPh4)[Mn12O12(O2CCHCl2)16(H2O)4] and (PPh4)2[Mn12O12(O2CCH2Cl)16(H2O)3] have been obtained. For (PPh4)2[Mn12O12(O2CCH2Cl)16(H2O)3], the data confirm an S = 10 ground state, and magnetization vs dc field scans on a pristine crystal exhibit hysteresis loops possessing steps due to quantum tunneling of magnetization (QTM). In addition, two forms of the cluster have been identified in the crystal with distinctly different relaxation barriers, with the faster-relaxing form being the majority one in pristine crystals from mother liquor, and the slower-relaxing one becoming the majority one in vacuum-dried samples. Similar behavior is seen for (PPh4)[Mn12O12(O2CCHCl2)16(H2O)4] with an S = 19/2 ground state, which shows three forms to be present in the hysteresis loops of a pristine crystal, all converting to a slow-relaxing form on vacuum-drying. High-frequency EPR spectra of the latter confirm a high axial anisotropy with D = −0.477 cm−1 and rationalize its effective relaxation barrier Ueff = 57 K. The combined work emphasizes a high sensitivity of such ultra-small nanomagnets to environmental influences, affecting their properties significantly, especially their quantum properties that are so important to many potential new 21st century applications.