Spectroscopic and magnetic properties of [FeL₂(salacen)]PF₆(L = imidazole or N-methylimidazole): new examples of intermediate electronic relaxation between S=½ and S=52 states. X-Ray crystal structure of [Fe(Him)₂(salacen)]PF₆

Abstract

Kumamoto 860, JapanThe iron(iii) complexes [Feb(salacen)] PF, [L = imidazole (Him) or N-methylimidazole (mim), salacen = ethylene (N-acetylacetonylideneimi nate) ("-a-meth ylsalicyliden&minate) ] were synthesized, and the phenomenon of the spin transition between high-spin (S =f) and low-spin (S = +) states depending on temperature was confirmed by temperature-dependent magnetism and Mossbauer spectra. The time-averaged Mossbauer spectra between the high-spin and low-spin states were observed for [Fe(mim),(salacen)] PF, . A stochastic model was proposed to estimate a spin-interconversion rate from the Mossbauer spectra of spin-crossover complexes. The spininterconversion rates of 6.7 x 1 Os s-' at 298 K and 3.1 x 1 0, s-' at 221 K were estimated using the model. Crystals of [Fe(Him),(salacen)]PF, are triclinic, space group P i , with a = 10.642(2), b = 12.771 (3), c = 9.430(1) A, 01 = 89.69(1), = 104.03(1), y = 96.97(2)", and Z = 2. The average bond distances F e N 1.970 and Fe-0 1.895 A are in good agreement with the corresponding values reported for low-spin isomers of other spin-crossover iron(iii) complexes.

Infinite Chain Structure and Steep Spin Crossover of a FeIII Complex with a N3O2 Pentadentate Schiff-Base Ligand and 4-Aminopyridine

“…At 293 K, the Fe-N and Fe-O bond distances are distributed in the range of 1.908(2)-2.257(2) # A, whose values are in the expected range for HS Fe III complexes with the Schiff-base type N 4 O 2 environment. 7,8 At 90 K, the Fe-N and Fe-O bond distances are distributed in the range of 1.870(2)-2.091(2) # A, whose values are in the expected range for LS Fe III complexes with the Schiff-base type N 4 O 2 environment. Among the six coordination bonds, the bond lengths of the Fe-N(2) (central amine nitrogen) and Fe-N(4) (4-aminopyridine) are much reduced associated with the spin transition.…”

Spin crossover iron(III) complexes

“…[Fe(salacen)(Him) 2 ]PF 6 ( Fig. 3b) [39] and [Fe(salacen)(N-imidazole) 2 ]PF 6 have FeN 4 O 2 chromophores with quadridentate salacen 2− and they are classified into SE type with gradual and incomplete SCO [39]. The spin interconversion in these SCO complexes also occurs in organic solvents at 200-300 K and thermochromism was observed from green at 200 K to purple at 300 K. …”

Iron(III) Spin Crossover Compounds

“…at room temperature. In contrast, the N-methyl-imidazole derivative is high spin at room temperature but a gradual transition to the low spin state takes place between 300 and 200 K [184]. Both compounds exhibit striking thermochromism in organic solvents, being purple at room temperature and green at ca.…”

“…15) may be considered as providing a field strength intermediate between that of salen and acen. The structure of [Fe(salacen)(Him) 2 ]PF 6 has been determined at 293 K, where 83% of the Fe(III) ions are low spin [184]. Both the Fe-O (1.879(6) ) and the Fe-N (1.912(7) ) bond distances associated with the salicylideneimine residue are shorter than those associated with the acetylacetonylideneimine residue (1.911(5) and 1.936(6) , respectively) [184].…”

“…The structure of [Fe(salacen)(Him) 2 ]PF 6 has been determined at 293 K, where 83% of the Fe(III) ions are low spin [184]. Both the Fe-O (1.879(6) ) and the Fe-N (1.912(7) ) bond distances associated with the salicylideneimine residue are shorter than those associated with the acetylacetonylideneimine residue (1.911(5) and 1.936(6) , respectively) [184]. [Fe(salacen)(Him) 2 ]PF 6 shows the onset of gradual spin crossover at about 200 K, reaching a magnetic moment of 2.83 B.M.…”