Different Ground Spin States in Iron(III) Complexes with Quadridentate Schiff Bases:  Synthesis, Crystal Structures, and Magnetic Properties

Abstract

The synthesis, structure, and magnetic characterization of [Fe(L1)(HIm)2] Y (Y = ClO4 - (1a), PF6 - (1b), and BPh4 - (1c)), [Fe(L2)(HIm)2]ClO4 (2a), [Fe(L2)(HIm)2]ClO4·H2O (2b), [NaFe(L2)(HIm)2(ClO4)2] (2c), [Fe(L3)(HIm)2]ClO4 (3), [Fe(L4)(HIm)2]ClO4 (4a), and [Fe(L4)(HIm)2] BPh4·H2O (4b) are reported (L1 = N,N‘-3,4-toluenebis(3-ethoxysalicylideneimine), L2 = N,N‘-4-chloro-o-phenylenebis(3-methoxysalicylideneimine), L3 = N,N‘-4-chloro-o-phenylenebis(3-ethoxysalicylideneimine), L4 = N,N‘-1,2-propylenebis(3-methoxysalicylideneimine), and HIm = imidazole). Compound 1a crystallizes in the triclinic system, space group P1̄, Z = 2, with a = 10.609(3) Å, b = 10.762(3) Å, c = 15.043(3) Å, α = 105.13(2)°, β = 90.67(2)°, and γ = 102.09(2)°. Compound 2c crystallizes in the monoclinic system, space group C2/c, Z = 4, with a = 14.969(6) Å, b = 17.324(6) Å, c = 13.050(10) Å, and β = 100.85(6)°. Compound 4a crystallizes in the orthorhombic system, space group P212121, Z = 4, with a = 12.402(2) Å, b = 14.354(2) Å, c = 15.773(2) Å. The structures of 1a and 4a are made up of discrete [Fe(L1)(HIm)2]+ and [Fe(L4)(HIm)2]+ cationic units, while 2c consists of dinuclear neutral entities [NaFe(L2)(HIm)2(ClO4)2]. The iron(III) ion is six-coordinated, the equatorial plane being occupied by the cis tetradentate Schiff base and the axial positions by the imidazole ligands. The metal−ligand bond distances as well as the relative orientation of the imidazole ligands are discussed in relation with the spin state of the title compounds. The magnetic properties reveal that 1a − c, 2a, 3, and 4b are high-spin species while 2c is a low-spin complex, and 2b and 4a display spin-crossover behavior. The thermodynamic model of Slichter and Drickamer was applied to account for the temperature variable high-spin molar fraction deduced from the magnetic behavior. The intermolecular interaction parameter, Γ, the enthalpy, ΔH, and the entropy, ΔS, changes associated with the spin transition of 2b were estimated as Γ = 1.6 kJ mol-1, ΔH = 12 kJ mol-1, and ΔS = 60 J mol-1 K-1.

Synthesis, Structure, and Magnetic Properties of a Tris[3-(2-pyridyl)-1,2,4-triazole]iron(II) Spin-Crossover Complex

“…It is known that in a few systems the solvent molecules are essential for the spin transition. [43,44] It seems likely that in the present system, due to a non-uniform distribution of water molecules in the lattice, some Fe II ions remain in the high-spin state.…”

Structural diversity in schiff base complexes of Ga(III), In(III), Pb(II), and Zn(II): Precursors and model systems for conducting metallopolymers

“…The methoxy groups located on the salcylidenimine do not participate in coordination. Previously reported crystal structures show that the methoxy group can participate in metal coordination, however in this instance, it does not [17][18][19][20][21][22][23][24][25][26]. Dimerization of gallium salen complexes was previously reported by Atwood who observed the dimerization of gallium salen complexes through close Ga-H interactions [27].…”

Effects of Metal Doping on the Spin-Crossover Properties of an Iron(II) Complex with Extended π-Conjugated Schiff-Base Ligand Having an N4O2 Donor Set

“…In the solid state, spin transitions between LS and HS states depend strongly on cooperativity, which is sensitive to the coupling between the adjacent spin centers, metaldonor bond length, and the crystal lattice vibrations. 15 Hence, it is possible for these complexes to affect a spin transition in a certain range by variation of the intermolecular interaction of compounds. Metal doping is an available strategy to control and adjust these interactions.…”

“…15 Hence, it is possible for these complexes to affect a spin transition in a certain range by variation of the intermolecular interaction of compounds. Metal doping is an available strategy to control and adjust these interactions.…”