2 research outputs found
[Fe(nsal<sub>2</sub>trien)]SCN, a New Two-Step Iron(III) Spin Crossover Compound, with Symmetry Breaking Spin-State Transition and an Intermediate Ordered State
We report the synthesis of the ironÂ(III)
complex of the hexadentate Schiff base ligand nsal<sub>2</sub>trien
obtained from the condensation of triethylenetetramine and 2 equiv.
of 2-hydroxy-1-naphthaldehyde. The study of the salt [FeÂ(nsal<sub>2</sub>trien)]ÂSCN (<b>1</b>) by magnetic susceptibility measurements
and Mössbauer spectroscopy reveals a rather unique behavior
that displays thermally induced spin crossover (SCO) with two well-separated
steps at 250 (gradual transition) and 142 K (steep transition). Single
crystal X-ray structures were obtained at 294, 150, and 50 K, for
the high spin (HS), intermediate (Int), and low spin (LS) phases.
The HS and LS phases are isostructural, and based on a single Fe<sup>III</sup> site (either HS or LS) an unusual symmetry break occurs
in the transition to the Int ordered phase, where the unit cell includes
two distinct Fe<sup>III</sup> sites and is based on a repetition of
the [HS–LS] motif. The two-step SCO behavior of <b>1</b> must result from the existence of structural constraints preventing
the full conversion HS ↔ LS in a single step
Thermal Hysteresis in a Spin-Crossover Fe<sup>III</sup> Quinolylsalicylaldimine Complex, Fe<sup>III</sup>(5-Br-qsal)<sub>2</sub>Ni(dmit)<sub>2</sub>·solv: Solvent Effects
The
Fe<sup>III</sup> complexes FeÂ(5-Br-qsal)<sub>2</sub>NiÂ(dmit)<sub>2</sub>·solv with solv = CH<sub>2</sub>Cl<sub>2</sub> (<b>1</b>) and (CH<sub>3</sub>)<sub>2</sub>CO (<b>2</b>) were synthesized,
and their structural and magnetic properties were studied. While magnetization
and Mössbauer spectroscopy data of <b>1</b> showed a
gradual spin transition, compound <b>2</b> evidenced an abrupt
transition with a thermal hysteresis of 13 K close to room temperature
(<i>T</i><sub>1/2</sub> ↓ ∼273 K and <i>T</i><sub>1/2</sub> ↑ ∼286 K). A similar packing
arrangement of segregated layers of cations and anions was found for <b>1</b> and <b>2</b>. In both low-spin, LS, structures there
are a large number of short intra- and interchain contacts. This number
is lower in the high-spin, HS, phases, particularly in the case of <b>1</b>. The significant loss of strong π–π interactions
in the cationic chains and short contacts in the anionic chains in
the HS structure of <b>1</b> leads to alternating strong and
weak bonds between cations along the cationic chains and the formation
of unconnected dimers along the anionic chains. This is consistent
with a significant weakening of the extended interactions in <b>1</b>. On the other hand, in the HS phase of <b>2</b> the
3D dimensionality of the short contacts observed in the LS phases
is preserved. The effect of distinct solvent molecules on the intermolecular
spacings explains the different spin crossover behaviors of the title
compounds