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Use of the Di-2-pyridyl Ketone/Acetate/Dicyanamide ?Blend? in Manganese(II), Cobalt(II) and Nickel(II) Chemistry: Neutral Cubane Complexes
Giannis S. Papaefstathiou
Albert Escuer
Franz A. Mautner
Catherine Raptopoulou
Aris Terzis
Spyros P. Perlepes
Ramon Vicente
{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).}
(EN)
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