High-spin tetranuclear iron(III) grids: Synthesis, crystal structure and magnetic properties

Abstract

Three new tetranuclear FeIII complexs Fe4L14Cl4 (1), Fe4L24(ClO4)4 (2), Fe4L34Cl45H2O (3) and a binuclear complex Fe2L4(MeOH)2Cl43MeOH (4) (the bis-Schiff base ligands H2L1–4 were obtained by the condensation of 2,4-dihydrazinopyrimidine and salicylicaldehyde or acetylacetone in a molar ratio of 1:2) have been synthesized and characterized by crystallography, spectroscopy and magnetic measurements. The tetranuclear 2×2 grid complex 1 crystallizes in a monoclinic space group C2/c with a=29.040(3)Å, b=10.9525(11)Å, c=26.881(3)Å, β=105.172(2)°, V=8251.9(15)Å3. Complex 2 crystallizes in a monoclinic space group P21 with a=12.536(3)Å, b=23.148(5)Å, c=17.506(4)Å, β=102.96(3)°, V=4950.6(17)Å3, and complex 3 in a triclinic space group P1¯ with a=12.145(2)Å, b=29.094(6)Å, c=29.343(6)Å, α=94.12(3)°, β=93.17(3)°, γ=97.62(3)°, V=10228(4)Å3. All the FeIII ions from 1, 2 and 3 are coordinated by an N4O2 sphere with two N atoms from pyrimidine, two N atoms from hydrazine, and two O atoms from phenoxo groups. Complex 4 has a binuclear structure crystallized in a triclinic space group P1¯ with a=10.500(2)Å, b=11.053(2)Å, c=15.990(3)Å, α=82.20(3)°, β=89.64(3)°, γ=70.77(3)°, V=1734.4(6)Å3. Magnetic susceptibility measurements indicate that the Fe(III) ions are all high spin, and adjacent Fe(III) ions are weakly antiferromagnetically coupled via pyrimidine in complexes 1, 2, 3 and 4. Magneto-structural correlation studies show that a longer Fe–Npym bond distance corresponds to a weaker antiferromagnetic coupling.