Synthesis, Structural Characterization (X-ray and EXAFS), and Magnetic Properties of Polynuclear Manganese(II) Complexes with Chlorobenzoato Bridges

Three different types of polynuclear Mn II complexes with carboxylate bridges were obtained from the reaction of Mn(RCOO) 2 with 2,2‘-bipyridine (bpy). Dinuclear complexes [Mn 2 (μ-RCOO) 2 (bpy) 4 ](ClO 4 ) 2 with R = 2-ClPh, 3-ClPh, 4-ClPh, Ph ( 1 − 4 ); trinuclear complexes [Mn 3 (μ-RCOO) 6 (bpy) 2 ] with R = 2-ClPh, 3-ClPh ( 5, 6 ), [Mn 3 (μ-RCOO) 6 (2,2‘-Me 2 -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 ). [Mn 2 (μ-PhCOO) 2 (bpy) 4 ](ClO 4 ) 2 ( 4 ) and the [Mn(μ-3-ClPhCOO) 2 (bpy)] n · n H 2 O ( 10 ) have been characterized by X-ray diffraction. Complex 4 crystallizes in the triclinic system, space group P 1̄ 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 C 2/ 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.