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

Abstract

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 [MnII(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 [Mn8O2(OH)2(O2CPh)10{(ph)(2‐py)CNO}4]· 4CH2Cl2 (2·4CH2Cl2) in about 55% yield. A second synthetic procedure that leads to pure 2 involves the reaction between the known starting material (NnBu4)[Mn4IIIO2(O2CPh)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 [Mn8(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(O2CPh)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 [Mn4III(μ3‐O)2]8+ subcore. The results for 3 reveal weak antiferromagnetic coupling, with J = −2.7 cm−1 for adjacent MnII ions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The use of di-2-pyridyl ketone in manganese(II) benzoate chemistry: Two novel linkage isomers containing the ketone form of the ligand and a neutral cubane containing the ligand in its gem-diolate(-1) form

“…The six-membered chelating ring Mn(1)N(1)C(5)C(6)C(7)N(2) adopts a slight boat conformation with the Mn(1) and C(6) atoms 0.032 and 0.099 Å , respectively, below the plane defined by the remaining four atoms. The Mn-N and Mn-O bond lengths agree well with the values expected for octahedral high-spin Mn(II) complexes [21]. Complex 1 is characterized by moderate Mn(1)-O(7) (2.346(3) Å ) and Mn(1)Á Á ÁMn(2) (3.552(2) Å ) distances and can be placed in class II in the ''carboxylate shift" classification scheme established by Lippard [22].…”

“…Complexes 1 and 2 Á 2MeCN join a small family of trinulear Mn(II) carboxylate complexes containing the {Mn 3 (g 1 :g 1 :l 2 -O 2 CR) 6 } unit [21,22,25].…”

Two new carboxylate–oxygen bridged trinuclear M(II) (MMn and Co) compounds with zwitterionic dicarboxylate ligands: crystal structures and magnetism

“…In the previous related reports, we note that although a dozen of compounds with similar bridges were characterized structurally and magnetically, no unambiguous correlations were found between the structural parameters (such as Mn-O bridge -Mn angles and the bond parameters of the syn-syn carboxyalte bridges) and the J values due to the complexity arising from the coexistence of mixed oxygen and carboxylate bridges, the presence of unpaired five electrons per Mn(II) and the effects of the terminal ligands. Compound 1 shows a relatively weaker interaction than the previous compounds which may be accounted for the longer Mn-O bridge distance (2.37 Å, 2.49 Å) and the Mn⋯Mn distance (3.69 Å, 3.76 Å) spanned by the mixed bridges than those (2.18-2.33 Å for Mn-O bridge and 3.43-3.69 Å for Mn⋯Mn distance) for the previous reported compounds [23][24][25][26][36][37][38][39].…”

The first tridecanuclear nickel(II) cluster: [Ni13(OH)6(O2CMe)8(btaO)12(H2O)6(nPrOH)4] (btaOH=1-hydroxybenzotriazole)

“…The presence of hydroxo ligands in 1 is manifested by a medium band at $3420 cm À1 [22]. The medium intensity band at 1170 cm À1 is assigned to m(N-O) [8c].…”