Exchange bias in Ni4 single-molecule magnets

The syntheses and physical properties are reported for three single-molecule magnets (SMMs) with the composition [Ni(hmp)(ROH)Cl]4, where R is CH3 (complex 1), CH2CH3 (complex 2) or CH2CH2C(CH3)3 (complex 3) and hmp is the monoanion of 2-hydroxymethylpyridine. The core of each complex is a distorted cube formed by four Ni ions and four alkoxide hmp oxygen atoms at alternating corners. Ferromagnetic exchange interactions give a S /4 ground state. Single crystal highfrequency EPR spectra clearly indicate that each of the complexes has a S /4 ground state and that there is negative magnetoanisotropy, where D is negative for the axial zero-field splitting DŜz . Magnetization versus magnetic field measurements made on single crystals with a micro-SQUID magnetometer indicate these Ni4 complexes are SMMs. Exchange bias is seen in the magnetization hysteresis loops for complexes 1 and 2. # 2003 Elsevier Science Ltd. All rights reserved.