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Synthesis, Structure and Characterisation of New Phenolato‐Bridged Manganese Complexes [L 2 Mn 2 ] 2+ − Formation by Ligand Oxidation in L a H [L a H = N ‐(2‐hydroxybenzyl)‐ N , N ′‐bis(2‐pyridylmethyl)ethane‐1,2‐diamine]
Author(s) -
Hureau Christelle,
AnxolabéhèreMallart Elodie,
Nierlich Martine,
Gonnet Florence,
Rivière Eric,
Blondin Geneviève
Publication year - 2002
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/1099-0682(200210)2002:10<2710::aid-ejic2710>3.0.co;2-k
Subject(s) - chemistry , acetonitrile , ligand (biochemistry) , crystallography , manganese , magnetic susceptibility , antiferromagnetism , octahedron , cyclic voltammetry , electrochemistry , imine , ion , stereochemistry , crystal structure , organic chemistry , biochemistry , physics , receptor , electrode , condensed matter physics , catalysis
A mononuclear [L a Mn III OAc](ClO 4 )·0.5H 2 O [ 2 (ClO 4 )·0.5H 2 O] complex with a new amino‐containing pentadentate ligand L a H with a [N 4 O] coordination sphere has been obtained. Magnetic susceptibility measurements of 2 (ClO 4 )·0.5H 2 O indicated a high spin electronic configuration for the Mn III ion. In cyclic voltammetry the reversible wave observed at E 1 / 2 = 0.15 V vs. SCE was attributed to the reduction of Mn III into Mn II . In acetonitrile solution complex 2 spontaneously evolved into phenolato‐bridged Mn II Mn II dimeric complexes with the concomitant oxidation of the ligand. X‐ray diffraction structures revealed that there is indeed a 1:1 mixture of two closely related complexes: in one case both ligands L a − have been oxidised to the imine form leading to the [L i Mn II Mn II L i ] 2+ cation ( 1a ), whereas in the other, only one ligand has been oxidised, leading to the [L a Mn II Mn II L i ] 2+ cation ( 1b ). In both 1a and 1b , Mn II ions are in a distorted octahedral environment. Crystallographic data indicated that the Mn 2 O 2 core is similar for 1a and 1b. The complete spectroscopic and electrochemical studies performed on powder samples and on acetonitrile solutions did not allow one to distinguish between the two cations. The magnetic susceptibility measurements performed on a powder sample of 1 (BPh 4 ) 2 ·2CH 3 COCH 3 was characteristic of a weak antiferromagnetic coupling interaction between the two high‐spin Mn II ions ( g = 1.95 and J = −1.5 cm −1 ). Similar behaviour was observed for the powder sample of 1 (ClO 4 ) 2 ·H 2 O ( g = 1.96 and J = −2.9 cm −1 ). Powder samples of 1 (BPh 4 ) 2 ·2CH 3 COCH 3 and 1 (ClO 4 ) 2 ·H 2 O showed EPR intensity variations with temperature indicating that the signal was mainly due to the S = 2 spin state. EPR spectra run on the acetonitrile solutions indicated that the dinuclear structure of 1 is maintained. In cyclic voltammetry, complex 1 (ClO 4 ) 2 ·H 2 O exhibited a quasi‐reversible wave in oxidation at E p = 0.71 V vs. SCE, attributed to the slow electron transfer of the Mn II Mn II /Mn II Mn III redox process ( k s app = 1.10 −4 cm 2 ·s −1 ). (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)