Use of the Di-2-pyridyl ketone/acetate/dicyanamide "blend" in manganese(II), cobalt(II) and nickel(II) chemistry: Neutral cubane complexes

The use of di-2-pyridyl ketone [(2-py)(2)CO]/dicyanamide "blend" in cobalt(II), manganese(II) and nickel acetate chemistry has yielded neutral cubane clusters. The preparation of [Mn-4(O2CMe)(2){N(CN)(2)}(2){(2-py)(2)C(OH)O}(4)]-2(2-py)(2)CO-4H(2)O (1) and [M-4(O2CMe)(2){N(CN)(2)}(2){(2-py)(2)C(OH)O}(4)]center dot 10H(2)O [M = Ni (2), Co (3)] was achieved by the reaction of [M(O2CMe)(2)]center dot 4H(2)O with (2-py)(2)CO and Na[N(CN)(2)] in MeOH/H2O (1:5, v/v) at room temperature. The metal(II)-mediated hydrolysis of (2-py)2CO to give the coordinated monoanion of the hydrate gem-diol form involves a nucleophilic attack of H2O on the carbonyl group. In the case of the cobalt reaction system, there is a second product. Upon employing an excess of (2-py)2CO, long reaction times, reflux conditions and high dilution, slow oxidation of Co-II takes place leading to the isolation of the mononuclear cobalt(111) complex [Co{(2-py)(2)C(OH)O}(2)][N(CN)(2)]center dot 4H(2)O (4) in yields higher than 70%. The structures of 1, 2 and 4 have been solved by single-crystal X-ray diffraction studies, while a unit-cell determination indicated that complex 3 is isostructural with 2. The tetranuclear cluster molecules of 1 and 2 have cubane [M-4(mu(3)-OR)(4)](4+) cores with divalent metal atoms and deprotonated oxygen atoms [originating from the (2-py)2C(OH)O- ligands] occupying alternate vertices. The centrosymmetric [Co{(2-py)(2)C(OH)O}(2)](+) cation of complex 4 has an octahedral structure with the (2-py)(2)C(OH)O- ligands adopting the tridentate N,O,N'-chelating coordination mode. The magnetic properties of 1-3 have been studied by variable-temperature dc magnetic susceptibility techniques. The studies indicate weak antiferromagnetic coupling for 1 and ferromagnetic behaviour for 2 and 3. A three-J model was found to be adequate for describing the thermal variation of the molar magnetic susceptibilities of 1 and 2. The magnetochemical results have been compared with literature data. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).