Structural variation in manganese complexes: Synthesis and characterization of manganese complexes from carboxylate-containing chelating ligands

Three manganese(II) complexes, [(Mn2L21)-L-II(H2O)(4)](ClO4)(2). H2O (1, (LH)-H-1 = (bis(2-pyridylmethyl)amino)acetic acid), [(Mn2L22)-L-II(H2O)(2)](BPh4)(2). 2EtoH . 2H(2)O (2, (LH)-H-2 = 3-(bis(2-pyridylmethyl)amino)propionic acid), {[(Mn2L22)-L-II(H2O)-(MeCN)](BPh4)(2).2MeCN}(infinity) (3), and a manganese(IV) complex [(Mn2O2L22)-O-IV](ClO4)(2). 4H(2)O (4) were synthesized and characterized by X-ray crystallography. The compound 1 was a dinuclear Mn-2(II) complex which crystallized in the monoclinic crystal system, space group P2(1)/n, with Z = 4, a = 12.19(1) Angstrom, b = 14.623(8) Angstrom, c = 21.72(1) Angstrom, beta = 96.29(6)degrees, V = 3849(4) Angstrom(3). The complex cation had an approximate C-2 symmtery. The two manganeses were both seven-coordinate and doubly bridged by one oxygen atom of carboxylate groups in mu(2),eta(1)-mode. The compound 2 was also a dinuclear Mn-2(II) complex which crystallized in the monoclinic crystal system, space group P2(1)/n, with Z = 2, a = 16.760(2) Angstrom, b = 9.643(2) Angstrom, c = 23.533(2) Angstrom, beta = 92.984(8)degrees, V = 3798.4(7) Angstrom(3). 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 P2(1)2(1)2(1), With Z = 4, a = 27.888(3) Angstrom, b = 29.054(2) Angstrom, c = 9.428(2) Angstrom, V = 7638(2) Angstrom(3). The cationic portion of 3 consisted of infinite chains of Mn-II (two Mn-II ions per an asymmetric unit) bridged by carboxylates in bidentate syn/anti mode. The compound 4 was a dinuclear bis(mu-oxo) Mn-2(IV) complex which crystallized in the trigonal crystal system, space group R (3) over bar, with Z = 8, a = 23.962(4) Angstrom, c = 17.190(3) Angstrom, V = 8547(3) Angstrom(3). All these structures are made up from a common fragment "(LMn)-Mn-n" assembling in various topologies. Variable-temperature magnetic susceptibility measurements revealed that the Mn-II 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 Mn-IV ions in 4 were strongly antiferromagnetically coupled (J = -97.5(5) cm(-1)). The cyclic voltammogram of 4 showed two reduction waves with E-1/2 values of -0.52 and 0.28 V (vs ferrocene). These Etc! values are more negative by 0.1 V than those of the closely related complex [(MnMnO2L21)-Mn-III-O-IV](ClO4).