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

Abstract

Three manganese(II) complexes, [Mn(II)(2)L(1)(2)(H(2)O)(4)](ClO(4))(2).H(2)O (1, L(1)H = (bis(2-pyridylmethyl)amino)acetic acid), [Mn(II)(2)L(2)(2)(H(2)O)(2)](BPh(4))(2).2EtOH.2H(2)O (2, L(2)H = 3-(bis(2-pyridylmethyl)amino)propionic acid), {[Mn(II)(2)L(2)(2)(H(2)O)(MeCN)](BPh(4))(2).2MeCN}(infinity) (3), and a manganese(IV) complex [Mn(IV)(2)O(2)L(2)(2)](ClO(4))(2).4H(2)O (4) were synthesized and characterized by X-ray crystallography. The compound 1 was a dinuclear Mn(II)(2) complex which crystallized in the monoclinic crystal system, space group P2(1)/n, with Z = 4, a = 12.19(1) Å, b = 14.623(8) Å, c = 21.72(1) Å, beta = 96.29(6) degrees, V = 3849(4) Å(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 &mgr;(2),eta(1)-mode. The compound 2 was also a dinuclear Mn(II)(2) complex which crystallized in the monoclinic crystal system, space group P2(1)/n, with Z = 2, a = 16.760(2) Å, b = 9.643(2) Å, c = 23.533(2) Å, beta = 92.984(8) degrees, V = 3798.4(7) Å(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) Å, b = 29.054(2) Å, c = 9.428(2) Å, V = 7638(2) Å(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(&mgr;-oxo) Mn(IV)(2) complex which crystallized in the trigonal crystal system, space group R&thremacr;, with Z = 8, a = 23.962(4) Å, c = 17.190(3) Å, V = 8547(3) Å(3). All these structures are made up from a common fragment "L(n)()Mn" 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 E(1/2) values are more negative by 0.1 V than those of the closely related complex [Mn(III)Mn(IV)O(2)L(1)(2)](ClO(4)).