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Keywords:

  • Spin crossover;
  • Schiff bases;
  • Mössbauer spectroscopy;
  • Magnetic properties;
  • Liquid crystals

Abstract

The synthesis and characterization of a series of mononuclear tripodand-based FeII complexes by means of Mössbauer andUV/Vis spectroscopic as well as magnetic methods is reported. The complexes were obtained from the reactions of FeII salt with heterocyclic aldehydes (imd = imidazole-4(5)-carboxaldehyde, py = picolinaldehyde, or 6-Mepy = 6-methylpicolinaldehyde) and a symmetric triamine [tren = tris(2-aminoethyl)amine, tame = 2,2,2-tris(aminomethyl)ethane, or tach = 1,3,5-cis,cis-cyclohexanetriamin]. Because of extreme rigidity of the capping triamine tach, the molecular structure of {Fe[tach(imd)3](BF4)2} (1) features an unprecedented tapered trigonal prismatic FeN6 polyhedron. The molecular structures of the complexes {Fe[tach(py)3](ClO4)2} (2), {Fe[tame(imd)3](ClO4)2} (3), {Fe[tame(py)3](ClO4)2} (4) and {Fe[tame(6-Mepy)3](ClO4)2} (5) are quite similar and exhibit pseudo-octahedral arrangements of the coordination polyhedron. Compound 1 is in the high spin state, whereas compounds 25 are in the low spin state at all investigated temperatures (10–400 K). Chemical modification of the ligands in 25 to introduce liquid crystalline properties is expected to decrease the ligand field strength sufficiently to transform the electronic LS ground state to spin crossover behavior in the room temperature region.