High pressure and very low temperature effects on the crystal structures of some iron(II) complexes

The crystal structures at 30 K of two iron(II) complexes, and their comparison with higher temperature crystal structures indicate that outside of the spin transition range, the only intramolecular modification comes from dynamical aspects. The contraction of the packing is strong from 110 to 30 K and similar in both complexes. The high pressure (0.16 GPa. 0.40 GPa) crystal structures of another iron(II) complex of the same family show that strong changes are induced cinder pressure within the packing but that to a first approximation, the effects of temperature (11 K) or pressure (0.40 GPa) on the intermolecular contacts are very similar even though one S...C intermolecular contact is significantly different. Moreover, slight differences in the cell parameter changes are noted. We also show that the deformation of thr iron(II) coordination sphere does not depend on the applied constraint but on the spin state only. (C) Academie des sciences , Editions scientifiques et medicales Elsevier SAS.