A Comparative XAS and X-ray Diffraction Study of New Binuclear Mn(III) Complexes with Catalase Activity. Indirect Effect of the Counteranion on Magnetic Properties

Abstract

Four new binuclear Mn(III) complexes with carboxylate bridges have been synthesized: [[Mn(nn)(H(2)O)](2)(mu-ClCH(2)COO)(2)(mu-O)](ClO(4))(2) with nn = bpy (1) or phen (2) and [[Mn(bpy)(H(2)O)](2)(mu-RCOO)(2)(mu-O)](NO(3))(2) with RCOO = ClCH(2)COO (3) or CH(3)COO (4). The characterization by X-ray diffraction (1 and 3) and X-ray absorption spectroscopy (XAS) (1-4) displays the relevance of this spectroscopy to the elucidation of the structural environment of the manganese ions in this kind of compound. Magnetic susceptibility data show an antiferromagnetic coupling for all the compounds: J = -2.89 cm(-1) (for 1), -8.16 cm(-1) (for 2), -0.68 cm(-1) (for 3), and -2.34 cm(-1) (for 4). Compounds 1 and 3 have the same cation complex [[Mn(bpy)(H(2)O)](2)(mu-ClCH(2)COO)(2)(mu-O)](2+), but, while 1 shows an antiferromagnetic coupling, for 3 the magnetic interaction between Mn(III) ions is very weak. The four compounds show catalase activity, and when the reaction stopped, Mn(II) compounds with different nuclearity could be obtained: binuclear [[Mn(phen)(2)](mu-ClCH(2)COO)(2)](ClO(4))(2), trinuclear [Mn(3)(bpy)(2)(mu-ClCH(2)COO)(6)], or mononuclear complexes without carboxylate. Two Mn(II) compounds without carboxylate have been characterized by X-ray diffraction: [Mn(NO(3))(2)(bpy)(2)][Mn(NO(3))(bpy)(2)(H(2)O)]NO(3) (5) and [Mn(bpy)(3)](ClO(4))(2).0.5 C(6)H(4)-1,2-(COOEt)(2).0.5H(2)O (8).

New dimanganese(III) complexes of pentadentate (N2O3) Schiff base ligands with the [Mn2(μ-OAc)(μ-OR)2]3+ core: Synthesis, characterization and mechanistic studies of H2O2 disproportionation

“…Although the structure of these enzymes has been determined, their catalytic mechanism is still poorly understood and the functional role of the bridges is yet unclear. Owing to their potential application as therapeutic agents against oxidative stress and as catalysts for bleaching and organic chemistry, a large number of dinuclear manganese complexes including various types of ligands have been synthesized and structurally characterized and many model complexes have been reported that show catalase activity [9][10][11][12][13][14][15][16]. An exhaustive and comprehensive review of the relevant research has recently been made [17].…”

Syntheses, structures, and photochemical properties of (μ3-O)tris{bis(μ-carboxylato)}trimanganese complexes with naphthylacetate ligands with relevance to artificial solar energy-harvesting systems

“…E is associated with Mn 1s transitions into p-like states with t 1u symmetry, and M is the main peak of the Mn K absorption spectrum. It has been shown that the position of the K-edge depends on the oxidation state of the manganese and the nature of the ligands [34]. The XANES analysis data for 2 are nearly same as those for 1.…”

“…P is a pre-edge peak arising from a dipole-forbidden, but quadrupole-allowed, 1s ? 3d inner atomic transition in MO 5 N [34]. E is associated with Mn 1s transitions into p-like states with t 1u symmetry, and M is the main peak of the Mn K absorption spectrum.…”

Structure, magnetic properties, catalase activity and DFT studies of [Mn2(μ-RCOO)2(μ-OR)2]2+ type dinuclear manganese(III,III) complexes

“…Antiferromagnetic interactions with |J| values in the range 6-15 cm À1 have been reported for Type-I [7][8][9][10][11][12][13][14][15] and Type-II [16][17][18][19][20][21][22][23] complexes. Type-V [37][38][39][40][41][42][43][44][45][46][47][48] compounds are weakly coupled with |J| $ 3 cm À1 , with both ferromagnetic and antiferromagnetic examples known. Strongest interactions occur in Type-IV compounds which are all antiferromagnetic having |J| value in the range, 90-100 cm À1 .…”

“…A variety of Mn(III,III) complexes differing in their core units have been reported so far (Scheme 1). The core structures and observed MnÁ Á ÁMn distances of oxo-and alkoxo-bridged dimanganese(III,III) complexes are as follows: Type-I, [Mn 2 (l-OR) 2 ] 4+ , 3.00-3.04 Å [7][8][9][10][11][12][13][14][15]; Type-II, [Mn 2 (l-RCOO)(l-OR) 2 ] 3+ , 2.91-2.94 Å [16][17][18][19][20][21][22][23]; Type-III, [Mn 2 (l-RCOO) 2 (l-OR) 2 ] 2+ , 2.85-2.87 Å [24][25][26][27][28]; Type-IV, [Mn 2 O 2 ] 2+ , 2.64-2.75 Å [29][30][31][32][33][34][35][36]; Type-V, [Mn 2 (l-RCOO) 2 (l-O)] 2+ , 3.08-3.22 Å [37][38][39][40][41][42][43][44][45][46][47][48]. The first four types form complexes with coplanar equatorial planes and parallel Jahn-Teller axes, while in Type-V complexes the Jahn-Teller axes were inclined by 27-90°.…”