Abstract of Publication No. 517
Andreas Sieber, Colette Boskovic, Roland Bircher, Oliver Waldmann, Stefan T. Ochsenbein,
Grégory Chaboussant, Hans U. Güdel, Nadeschda Kirchner, Joris van Slageren,
Wolfgang Wernsdorfer, Antonia Neels, Helen Stoeckli-Evans, Stefan Janssen, Fanni Juranyi and Hannu Mutka
A new family of tetranuclear Ni complexes
[Ni4(ROH)4L4] (H2L =
salicylidene-2-ethanolamine; R = Me (1) or Et (2)) has been
synthesized and studied. Complexes 1 and 2 possess a
[Ni4O4] core comprising a distorted cubane arrangement.
Magnetic susceptibility and inelastic neutron scattering studies indicate a
combination of ferromagnetic and antiferromagnetic pairwise exchange
interactions between the four NiII centers, resulting in an S
= 4 spin ground state. Magnetization measurements reveal an easy-axis-type
magnetic anisotropy with D -0.93
cm–1 for both complexes. Despite the large magnetic
anisotropy, no slow relaxation of the magnetization is observed down to 40 mK.
To determine the origin of the low-temperature magnetic behavior, the magnetic
anisotropy of complex 1 was probed in detail using inelastic neutron
scattering and frequency domain magnetic resonance spectroscopy. The
spectroscopic studies confirm the easy-axis-type anisotropy and indicate strong
transverse interactions. These lead to rapid quantum tunneling of the
magnetization, explaining the unexpected absence of slow magnetization
relaxation for complex 1.