Toward chiral iron(II) spin-crossover grafted resins with imidazole Schiff-base ligands

Using chiral imidazole Schiff-base as ligands, two couples of mononuclear iron(II) enantiomeric complexes fac-Lambda-[Fe(R-L)(3)](ClO4)(2)center dot H2O (1), fac-Delta-[Fe(S-L)(3)](ClO4)(2)center dot H2O (2), fac-Lambda-[Fe(R-L)(3)](BF4)(2)center dot H2O (3), fac-Lambda-[Fe(S-L)(3)] (BF4)(2)center dot H2O (4) (L = 1-(2-naphthyl)-N-((1-methyl-imidazol-2-yl)methylene)ethanamine) have been successfully synthesized and characterized. The CD spectra of 1 and 2,3 and 4, were basically mirror images confirming their enantiomers. X-ray crystallography revealed that complexes 1-4 all crystallized in the chiral space group P213 with the iron(II) center surrounded by three bidentate ligands. Magnetic measurements revealed incomplete spin transition for 1, and gradual spin crossover (T-1/2 = 150 K) for 3. However, the spin-crossover behaviors were vanished after grafting 1-4 to the Merrifield's peptide resin, and the iron(II) centers in the resin remained in a high-spin state in the temperature range of 2-300 K. (C) 2015 Elsevier B.V. All rights reserved.