Anthony KERMAGORET - THESES ET MEMOIRES DE L'UDS

Chapitre III
Considering the spin topology described in Figure S-5 and assuming each pairwise
interaction is describable in terms of the Heisenberg Hamiltonian of the form Ĥ = -Jij Ŝi⋅Ŝj, the
complete spin Hamiltonian for Ni4 is given in eq. 1
Ĥ = -J1 Ŝ1⋅Ŝ2 - J2 Ŝ1⋅Ŝ4 - J3Ŝ1⋅Ŝ3 - J2 Ŝ2⋅Ŝ3 - J1 Ŝ3⋅Ŝ4 (1)
As explained by Griffith and by Hendrickson, the existence of three different exchange
constants for this peculiar spin topology prevents the use of the Kambe vector-coupling
[S ,S ,S ]
approach. 4 5 6 Unfortunately, in the present case, no analytical fitting by full diagonalization of
the complete spin Hamiltonian was successful in the whole temperature range. This may infirm the
hypothesis of Heisenberg type interactions.
The magnetic properties of this compound require further studies, for instance by neutron
diffraction, neutron scattering, or high-field EPR spectroscopy, in order to precise the amplitude and
sign of the different exchange constants and the characteristics of the ground state (spin value,
anisotropy).
5. Crystallographic
5.1 X-ray data collection, structure solution and refinement for 1a⋅2CH2Cl2, 3 and 4.
Suitable crystals for X-ray analysis of compounds 1a⋅2CH2Cl2, 3 and 4 were obtained by
layering hexane on dichloromethane solutions. The intensity data was collected at 173(2) K on a
[S- ]
Kappa CCD diffractometer 7 (graphite monochromated MoKα radiation, λ = 0.71073 Å).
Crystallographic and experimental details for the structures are summarized in Table S-1. The
structures were solved by direct methods (SHELXS-97) and refined by full-matrix least-squares
procedures (based on F 2 [S- ]
, SHELXL-97) 8 with anisotropic thermal parameters for all the non-
hydrogen atoms. The hydrogen atoms were introduced into the geometrically calculated positions
and refined riding on the corresponding parent atoms. For 1a, C2 and C6 were found disordered in
two positions with equal occupancy factors and their position was refined isotropically. CCDC-
641489 (3), 641490 (4) and 641491 (1a⋅2CH2Cl2) contain the supplementary crystallographic data
that can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax
(+44)1223-336-033 or deposit@ccdc.cam.ac.uk). Figure 1 was produced using the UCSF Chimera
package from the Computer Graphics Laboratory, University of California, San Francisco: C.C.
Huang, G.S. Couch, E.F. Pettersen, T.E. Ferrin, "Chimera: An Extensible Molecular Modeling
18