Effect of Cyanato, Azido, Carboxylato, and Carbonato Ligands on the Formation of Cobalt(II) Polyoxometalates: Characterization, Magnetic, and Electrochemical Studies of Multinuclear Cobalt Clusters

Abstract

Five Co(II) silicotungstate complexes are reported. The centrosymmetric heptanuclear compound K(20)[{(B-beta-SiW(9)O(33)(OH))(beta-SiW(8)O(29)(OH)(2))Co(3)(H(2)O)}(2)Co(H(2)O)(2)]47 H(2)O (1) consists of two {(B-beta-SiW(9)O(33)(OH))(beta-SiW(8)O(29)(OH)(2))Co(3)(H(2)O)} units connected by a {CoO(4)(H(2)O)(2)} group. In the chiral species K(7)[Co(1.5)(H(2)O)(7))][(gamma-SiW(10)O(36))(beta-SiW(8)O(30)(OH))Co(4)(OH)(H(2)O)(7)]36 H(2)O (2), a {gamma-SiW(10)O(36)} and a {beta-SiW(8)O(30)(OH)} unit enclose a mononuclear {CoO(4)(H(2)O)(2)} group and a {Co(3)O(7)(OH)(H(2)O)(5)} fragment. The two trinuclear Co(II) clusters present in 1 enclose a mu(4)-O atom, while in 2 a mu(3)-OH bridging group connects the three paramagnetic centers of the trinuclear unit, inducing significantly larger Co-L-Co (L=mu(4)-O (1), mu(3)-OH (2)) bridging angles in 2 (theta(av(Co-L-Co))=99.1 degrees ) than in 1 (theta(av(Co-L-Co))=92.8 degrees ). Weaker ferromagnetic interactions were found in 2 than in 1, in agreement with larger Co-L-Co angles in 2. The electrochemistry of 1 was studied in detail. The two chemically reversible redox couples observed in the positive potential domain were attributed to the redox processes of Co(II) centers, and indicated that two types of Co(II) centers in the structure were oxidized in separate waves. Redox activity of the seventh Co(II) center was not detected. Preliminary experiments indicated that 1 catalyzes the reduction of nitrite and NO. Remarkably, a reversible interaction exists with NO or related species. The hybrid tetranuclear complexes K(5)Na(3)[(A-alpha-SiW(9)O(34))Co(4)(OH)(3)(CH(3)COO)(3)]18 H(2)O (3) and K(5)Na(3)[(A-alpha-SiW(9)O(34))Co(4)(OH)(N(3))(2)(CH(3)COO)(3)]18 H(2)O (4) were characterized: in both, a tetrahedral {Co(4)(L(1))(L(2))(2)(CH(3)COO)(3)} (3: L(1)=L(2)=OH; 4: L(1)=OH, L(2)=N(3)) unit capped the [A-alpha-SiW(9)O(34)](10-) trivacant polyanion. The octanuclear complex K(8)Na(8)[(A-alpha-SiW(9)O(34))(2)Co(8)(OH)(6)(H(2)O)(2)(CO(3))(3)]52 H(2)O (5), containing two {Co(4)O(9)(OH)(3)(H(2)O)} units, was also obtained. Compounds 2, 3, 4, and 5 were less stable than 1, but their partial electrochemical characterization was possible; the electronic effect expected for 3 and 4 was observed.

Polyoxothiomolybdenum Wheels as Anionic Receptors for Recognition of Sulfate and Sulfonate Anions

“…Polyoxometalates (POMs) represent a family of inorganic compounds rich of thousands of compounds that are of current interest for recognized applications in catalysis, [1][2][3][4][5] medicine [6,7] magnetism, [8,9] or in supramolecular chemistry. [10][11][12][13][14] In marked contrast with POMs, polyoxothiometalates (POTMs) are far less common, but they can provide original compounds and especially transition-metal-ringlike clusters based on the self-condensation of [M 2 O 2 S 2 ] 2+ oxothiocations (M = Mo V or W V ).…”

The Ball‐Shaped Heteropolytungstates [{Sn(CH3)2(H2O)}24{Sn(CH3)2}12(A‐XW9O34)12]36− (X=P, As): Stability, Redox and Electrocatalytic Properties in Aqueous Media

“…26À [58] have been shown to be effective electrocatalysts for redox reactions involving NO x species in general and NO in particular. The interest in NO has grown considerably ever since its important role in biology was unveiled.…”

Di-μ1,1-azido-bis[(2-{1-[2-(isopropylamino)ethylimino]ethyl}phenolato)copper(II)]

“…Polynuclear complexes containing bridging groups are of great interest because of their versatile molecular structures and applications (Massoud et al, 2007;Lisnard et al, 2007;Sarkar et al, 2004). In the last few years chemists have dedicated their efforts to the study of molecular-based magnetic materials.…”