Synthesis, Structural Characterization (X-ray and EXAFS), and Magnetic Properties of Polynuclear Manganese(II) Complexes with Chlorobenzoato Bridges
Citations Over TimeTop 19% of 1998 papers
Abstract
Three different types of polynuclear MnII complexes with carboxylate bridges were obtained from the reaction of Mn(RCOO)2 with 2,2‘-bipyridine (bpy). Dinuclear complexes [Mn2(μ-RCOO)2(bpy)4](ClO4)2 with R = 2-ClPh, 3-ClPh, 4-ClPh, Ph (1−4); trinuclear complexes [Mn3(μ-RCOO)6(bpy)2] with R = 2-ClPh, 3-ClPh (5, 6), [Mn3(μ-RCOO)6(2,2‘-Me2-bpy)2] with R = 2-ClPh, 3-ClPh, 4-ClPh (7−9), and 1D complexes [Mn(μ-RCOO)2(bpy)]n with R = 3-ClPh, 4-ClPh (10, 11). [Mn2(μ-PhCOO)2(bpy)4](ClO4)2 (4) and the [Mn(μ-3-ClPhCOO)2(bpy)]n·nH2O (10) have been characterized by X-ray diffraction. Complex 4 crystallizes in the triclinic system, space group P1̄ with a = 9.1886(10) Å, b = 11.6135(9) Å, c = 13.595(2) Å, α = 66.225(13)°, β = 84.073(12)°, γ = 88.593(10)°, Z = 1. Complex 10 crystallizes in the monoclinic system, space group C2/c with a = 26.376(5) Å, b = 12.404(3) Å, c = 7.095(1) Å, β = 96.10(3)°, Z = 4. The other complexes were characterized by XANES and EXAFS studies, by comparison with analogous complexes of known X-ray crystal structure. The Mn···Mn distances in the dinuclear complexes and in the infinite chains were similar (av 4.5 Å) and longer than for the trinuclear complexes (av 3.6 Å); this is in agreement with the number of carboxylate bridges: two in the first case and three for the trinuclear complexes. All the polynuclear complexes shown very weak antiferromagnetic coupling (J between −0.7 and −3.22 cm-1). So, at low temperatures more than one spin state may be populated and many possible transitions may be expected in the EPR spectra; each series shows a similar spectrum, which is different from the others.
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