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Structural Variation in Manganase Complexes: Synthesis and Characterization of Manganese Complexes from Carboxylate-containing Chelating Ligands

1998; American Chemical Society; Volume: 37; Issue: 18 Linguagem: Inglês

10.1021/ic971184u

1520-510X

Hitoshi Iikura, Toshi Nagata,

Metal complexes synthesis and properties

Three manganese(II) complexes, [MnII2L12(H2O)4](ClO4)2·H2O (1, L1H = (bis(2-pyridylmethyl)amino)acetic acid), [MnII2L22(H2O)2](BPh4)2·2EtOH·2H2O (2, L2H = 3-(bis(2-pyridylmethyl)amino)propionic acid), {[MnII2L22(H2O)(MeCN)](BPh4)2·2MeCN}∞ (3), and a manganese(IV) complex [MnIV2O2L22](ClO4)2·4H2O (4) were synthesized and characterized by X-ray crystallography. The compound 1 was a dinuclear MnII2 complex which crystallized in the monoclinic crystal system, space group P21/n, with Z = 4, a = 12.19(1) Å, b = 14.623(8) Å, c = 21.72(1) Å, β = 96.29(6)°, V = 3849(4) Å3. The complex cation had an approximate C2 symmtery. The two manganeses were both seven-coordinate and doubly bridged by one oxygen atom of carboxylate groups in μ2,η1-mode. The compound 2 was also a dinuclear MnII2 complex which crystallized in the monoclinic crystal system, space group P21/n, with Z = 2, a = 16.760(2) Å, b = 9.643(2) Å, c = 23.533(2) Å, β = 92.984(8)°, V = 3798.4(7) Å3. The complex cation of 2 also had two seven-coordinate manganese ions, but unlike 1 the nonbridging carboxylate oxygens weakly coordinate to the manganese ions. The compound 3 crystallized in the orthorhombic crystal system, space group P212121, with Z = 4, a = 27.888(3) Å, b = 29.054(2) Å, c = 9.428(2) Å, V = 7638(2) Å3. The cationic portion of 3 consisted of infinite chains of MnII (two MnII ions per an asymmetric unit) bridged by carboxylates in bidentate syn/anti mode. The compound 4 was a dinuclear bis(μ-oxo) MnIV2 complex which crystallized in the trigonal crystal system, space group R3̄, with Z = 8, a = 23.962(4) Å, c = 17.190(3) Å, V = 8547(3) Å3. All these structures are made up from a common fragment "LnMn" assembling in various topologies. Variable-temperature magnetic susceptibility measurements revealed that the MnII ions in 1−3 were weakly antiferromagnetically coupled (J = −0.631(6), −0.655(5), and −0.20(1) cm-1 for 1−3), and that the MnIV ions in 4 were strongly antiferromagnetically coupled (J = −97.5(5) cm-1). The cyclic voltammogram of 4 showed two reduction waves with E1/2 values of −0.52 and 0.28 V (vs ferrocene). These E1/2 values are more negative by 0.1 V than those of the closely related complex [MnIIIMnIVO2L12](ClO4).