Reports: AC3
44200-AC3 Investigation of Polynuclear Transition Metal Complexes with Spin Transition
The current quest for increased capacity of information storage devices has fuelled intense research of molecule-based materials that can be bistable, i.e. that have two different states accessible within the same domain of environmental conditions. Numerous mononuclear coordination complexes of Fe(II) can adopt two different d-electron configurations, and consequently, two different spin states. Some of these complexes manifest bistability underscored by cooperativity based on strong intermolecular interactions exerted in solid state.
Our research is focused on the
investigation of molecules that can undergo spin transitions and contain
multiple Fe(II) ions, and in which the transition can
be affected by intramolecular interactions between the metal ions.
One of the type of molecules from this category that we study is that of pentanuclear, cyanide-bridged clusters {
the manifestation of a charge transfer induced spin transition (CTIST) in Co/Fe clusters
a spin transition between high spin (HS) and low spin (LS) FeII in the Fe/Fe and Fe/Co clusters
the first direct, experimental observation of uncompensated spin density at diamagnetic FeII metal ions that bridge the paramagnetic CrIII in the Fe/Cr clusters.
The CTIST
involves formal intramolecular electron transfer and
spin state changes at the metal ions within a molecule or material and creates
the potential for the control of the magnetic and optical properties by changes
in temperature or with irradiation. The
first report of such a phenomenon was made in 1996 and since then only several
molecule-based materials, including the {
In the last two
years we have investigated the new cyanide-bridged {
To investigate directly
the oxidation and spin state of the Fe sites of the cluster, we conducted
variable temperature, variable field Mössbauer studies. These studies showed that at low temperature
the Fe/Os cluster has a LS FeII/ OsIII configuration, and that at high temperature
there is no HS FeII being formed, which
excludes the possibility that a classical LS-to-HS transition is induced by
temperature at the FeII sites of the
cluster. Therefore the increase in the magnetic susceptibility with the temperature must be due to
a CTIST from OsIII(S = 1/2)-LS FeII(0) to OsII(S
= 0)-HS FeIII(S = 5/2). EPR studies conducted in collaboration with Professor
Doros Petasis from To our
knowledge, the { (1) is only the second example of cluster that contains the hexacyanoosmate(III) anion as a building block,
(2) contains at high temperature the first
example HS FeIII ion with a coordination
of four imines and two cyanides or isothiocyanides,
and
(3) exhibits an unprecedented type
of reversible, temperature-induced CTIST centered at room temperature from LS FeII-OsIII to HS FeIII-OsII, the first time that the LS FeII becomes HS FeIII,
thus undergoing the largest possible change in spin of DS = 5/2.
These unique results represent a
valuable addition to the relatively small literature on CTIST phenomenon. A manuscript reporting these results is
complete and will be submitted to Angewandte Chemie in October 2009.