1 research outputs found
The role of effectors of the activin signalling pathway, activin receptors IIA and IIB, and Smad2, in patterning of tooth development
The synthesis, crystal
structures, magnetic behavior, and electron
paramagnetic resonance studies of five new Fe<sup>III</sup> spin crossover
(SCO) complexes are reported. The [Fe<sup>III</sup>N<sub>5</sub>O]
coordination core is constituted of the pentadentate ligand bztpen
(N<sub>5</sub>) and a series of alkoxide anions (ethoxide, propoxide, <i>n</i>-butoxide, isobutoxide, and ethylene glycoxide). The methoxide
derivative previously reported by us is also reinvestigated. The six
complexes crystallize in the orthorhombic <i>Pbca</i> space
group and show similar molecular structures and crystal packing. The
coordination octahedron is strongly distorted in both the high- and
low-temperature structures. The structural changes upon spin conversion
are consistent with those previously observed for [Fe<sup>III</sup>N<sub>4</sub>O<sub>2</sub>] SCO complexes of the Schiff base type,
except for the FeâOÂ(alkoxide) bond distance, which shortens
significantly in the high-spin state. Application of the SlichterâDrickamer
thermodynamic model to the experimental SCO curves afforded reasonably
good simulations with typical enthalpy and entropy variations ranging
in the intervals Î<i>H</i> = 6â13 kJ mol<sup>â1</sup> and Î<i>S</i> = 40â50 J mol<sup>â1</sup> K<sup>â1</sup>, respectively. The estimated
values of the cooperativity parameter Î, found in the interval
0â2.2 kJ mol<sup>â1</sup>, were consistent with the
nature of the SCO. Electron paramagnetic resonance spectroscopy confirmed
the transformation between the high-spin and low-spin states, characterized
by signals at <i>g</i> â 4.47 and 2.10, respectively.
Electrochemical analysis demonstrated the instability of the FeÂ(II)
alkoxide derivatives in solution