  The first cobalt molecule to function as a single-molecule magnet,
[Co4(hmp)4(MeOH)4Cl4], where hmp- is the anion of hydroxymethylpyridine, is
reported. The core of the molecule consists of four Co(II) cations and four
hmp- oxygen atoms ions at the corners of a cube. Variable-field and
variable-temperature magnetization data have been analyzed to establish that
the molecule has a S=6 ground state with considerable negative
magnetoanisotropy. Single-ion zero-field interactions (DSz2) at each cobalt ion
are the origin of the negative magnetoanisotropy. A single-crystal of the
compound was studied by means of a micro-SQUID magnetometer in the range of
0.040-1.0K. Hysteresis was found in the magnetization versus magnetic field
response of this single crystal. It is concluded that this is the first cobalt
molecule to function as a single-molecule magnet.
