Novel Trinuclear Mn^II/Mn^II/Mn^II Complexes – Crystal Structures and Catalytic Properties

Abstract

The trinuclear manganese(II) complexes [Mn3(L1)2(μ‐OAc)4]·2Et2O {HL1 = (1‐hydroxy‐4‐nitrobenzyl)((2‐pyridyl)methyl)((1‐methylimidazol‐2‐yl)methyl)amine} (1·2EtOH), [Mn3(L2)2(μ‐OAc)4] {HL2 = ((1‐methylimidazol‐2‐yl)methyl)(1‐hydroxybenzyl)amine} (2) and [Mn3(L3)2(μ‐OAc)6] {L3 = bis(1‐methylimidazol‐2‐yl)methanone} (3) were synthesized. The compounds were characterized by X‐ray crystallography, mass spectrometry, IR, UV‐vis spectroscopy, and elemental analysis. The manganese atoms in 1 and 2 are bridged by phenol moieties of the ligands and acetates. In 3 they are only bridged by acetates in a mono‐ and bi‐dentate way. The resulting Mn···Mn distances are 3.233(1) Å (1), 3.364(1) Å (2) and 3.643(7) Å (3). In the present compounds different limiting cases for the phenomenon of the carboxylate shift are realized. Besides symmetric mono‐ and bi‐dentate bridging an unusual intermediate is also observed. 1·2EtOH is the first example of a trinuclear model for the OEC that shows catalase activity. Furthermore it was characterized by temperature dependent magnetic susceptibility measurements and a total spin ground state of St = 5/2 was found. The results for 1 reveals antiferromagnetic coupling between the central and the terminal manganese ions, with J = −1.2 cm−1, g = 2.00 (fixed), χTIP = 150×10−6 cm3mol−1.

Versatility in the Coordination Modes of n‐Chlorobenzoato Ligands: Synthesis, Structure and Magnetic Properties of Three Types of Polynuclear MnII Compounds

“…With 2-ClC 6 H 4 COO, only the trinuclear complex [Mn 3 (µ-2-ClC 6 H 4 COO) 6 (phen) 2 ] (1) was obtained, regardless of the Mn II /phen ratio or solvent (CH 3 CH 2 OH or CH 3 CN), as reported for the reaction with bpy. [21] With 3-ClC 6 H 4 COO, two compounds were obtained in both solvents: the trinuclear compound [Mn 3 (µ-3-ClC 6 H 4 COO) 6 (phen) 2 ] (2) when the Mn II /phen ratio was 3:2 and the 1D system [Mn(µ-3-ClC 6 H 4 COO) 2 (phen)] n (4) when the ratio was 1:1.…”

“…[21] With 3-ClC 6 H 4 COO, two compounds were obtained in both solvents: the trinuclear compound [Mn 3 (µ-3-ClC 6 H 4 COO) 6 (phen) 2 ] (2) when the Mn II /phen ratio was 3:2 and the 1D system [Mn(µ-3-ClC 6 H 4 COO) 2 (phen)] n (4) when the ratio was 1:1. This behaviour is different from that reported for the analogous reactions with bpy, [21] where, for both Mn II /bpy ratios, the trinuclear compound was obtained and the 1D system appeared as a by-product after filtration of the trinuclear complex.…”

“…2.39 Å). [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] The hexacoordination of the terminal Mn2 ion is completed by a 1,10-phenanthroline ligand. The Mn1···Mn2 distances are 3.630 and 3.546 Å for compounds 1 and 3, respectively, which agree with those reported in the literature (3.370-3.691 Å).…”

“…[21,22] With regard to dinuclear Mn II compounds, there are not many compounds with a [Mn 2 (µ-H 2 O)(µ-RCOO) 2 ] 2+ core reported in the literature, [34][35][36][37][38][39][40][41][42][43][44] and fewer whose magnetic properties have been studied [41][42][43][44] or whose EPR spectrum have been reported. [44] Here, we report the synthesis and characterization of three types of Mn II compounds with different nuclearity, with chlorobenzoato and 1,10-phenanthroline ligands: three trinuclear compounds [Mn 3 (µ-n-ClC 6 H 4 COO) 6 (phen) 2 ], where n = 2, 3, 4 (1-3), one 1D compound [Mn(µ-3-ClC 6 H 4 COO) 2 (phen)] n (4) and one neutral dinuclear compound [{Mn(4-ClC 6 H 4 COO)(phen)} 2 (µ-4-ClC 6 H 4 COO) 2 -(µ-H 2 O)] (5). Structural characterization of compounds 1, 3-5 was achieved by X-ray diffraction.…”

“…Carboxylate groups display a wide variety of coordination modes such as monodentate terminal, chelating, bidentate bridging and monodentate bridging modes (Figure 1), which lead to several types of compounds. There are some trinuclear compounds with a [Mn 3 (µ-RCOO) 6 ] core reported in the literature, [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] but only half of them are magnetically studied, [13][14][15][16][17][18][19][20][21][22] and even less have been characterized by EPR spectroscopy. [19][20][21][22][23] The number of described 1D Mn II chains with two carbox-4471 -2.8, -1.8 and -3.6 cm -1 for compounds 1-5, respectively.…”