Phenyl 2-pyridyl ketone and its oxime in manganese carboxylate chemistry: Synthesis, characterisation, X-ray studies and magnetic properties of mononuclear, trinuclear and octanuclear complexes

Phenyl 2-pyridyl ketone and its oxime in manganese carboxylate chemistry: Synthesis, characterisation, X-ray studies and magnetic properties of mononuclear, trinuclear and octanuclear complexes

Milios, C.J. Stamatatos, T.C. Kyritsis, P. Terzis, A. Raptopoulou, C.P. Vicente, R. Escuer, A. Perlepes, S.P.

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Επιστημονική δημοσίευση - Άρθρο Περιοδικού (EL)

Scientific publication - Journal Article (EN)

2004

The use of phenyl 2-pyridyl ketone [(ph)(2-py)CO] and its oxime [(ph)(2-py)CNOH] in manganese benzoate chemistry has been investigated. The reaction of an excess of (ph)(2-py)CNOH with Mn(O2CPh) 2·2H2O affords the mononuclear complex [Mn II(O2CPh)2{(ph)(2-py)CNOH}2] ·1.2H2O (1·1.2H2O) in high yield. The MnII ion is coordinated by two monodentate benzoates and two N,N′-bidentate chelating (ph)(2-py)CNOH molecules in a cis-cis-trans fashion. The comproportionation reaction between Mn(O2CPh) 2·2H2O and NnBu4MnO4 (3:1) in the presence of (ph)(2-py)CNOH in MeCN/EtOH/CH2Cl2 leads to the isolation of the mixed-valent cluster [Mn8O 2(OH)2(O2CPh)10{(ph)(2-py)CNO} 4]· 4CH2Cl2 (2·4CH 2Cl2) in about 55% yield. A second synthetic procedure that leads to pure 2 involves the reaction between the known starting material (NnBu4)[Mn4IIIO2(O 2CPh)9-(H2O)] and four equivalents of the oxime ligand in CH2Cl2. The centrosymmetric octanuclear molecule contains four MnII and four MnIII ions held together by two μ4-O2- ligands and two μ3-OH- ions to give the unprecedented [Mn 8(μ4-O)2(μ3-OH) 2]14+ core, with peripheral ligation provided by ten PhCO2- (two η1, four syn,syn η1:η1:μ2 and four η1:η2:μ3) and four η1:η1:η1:μ2 (ph)(2-py)CNO- ions. The 1:1 reaction between Mn(O 2CPh)2·2H2O and the ketone (ph)(2-py)CO affords the trinuclear complex [Mn3(O2CPh) 6{(ph)(2-py)CO}2] (3) in more than 80% yield. As judged from single-crystal X-ray crystallography, the complex adopts a linear structure with one η1:η2:μ2 and two η1:η1:μ2 benzoates spanning each pair of metal ions. The terminal MnII ions are capped by bidentate chelating (ph)(2-py)CO ligands. The three complexes have been characterised by IR spectroscopy. The CV study of complex 2 in CH2Cl2 reveals irreversible reduction and oxidation processes. The magnetic properties of 2 and 3 have been studied by variable-temperature dc magnetic-susceptibility techniques. As the temperature approaches zero, the value of the χMT product for 2 approaches zero and, thus, the octanuclear complex has an S = 0 ground state. This S = 0 ground state is explained in terms of the magnetic behaviour of the central, butterfly-like [Mn4 III(μ3-O)2]8+ sub-core. The results for 3 reveal weak antiferromagnetic coupling, with J = -2.7 cn -1 for adjacent MnII ions. © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004. (EN)

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