Octa- and Nonanuclear Nickel(II) Polyoxometalate Clusters: Synthesis and Electrochemical and Magnetic Characterizations

Abstract

Three high-nuclearity NiII-substituted polyoxometalate compounds functionalized by exogenous ligands have been synthesized and characterized. The octanuclear complexes in Na15[Na{(A-R-SiW9O34)Ni4(CH3COO)3(OH)3}2] . 4NaCl . 36H2O (1) and Na15[Na{(A-R-SiW9O34)Ni4(CH3COO)3(OH)2(N3)}2] . 32H2O (2) can be described as two {Ni4} subunits connected via a {Na(CH3COO)6} group, with the acetato ligands also ensuring in each subunit the connection between the paramagnetic centers. In 2, two azido groups replace two of the six mu-hydroxo ligands present in 1. The nonanuclear complex K7Na7[(A-R-SiW9O34)2Ni9(OH)6(H2O)6(CO3)3] . 42H2O (3) exhibits a double cubanestructure with two [(A-R-SiW9O34)Ni4(OH)3]5- subunits linked by three carbonato ligands. A ninth NiII center connected to one subunit via a carbonato ligand and a O=W group completes this asymmetric polyoxometalate.Electronic spectroscopy and electrochemical studies indicate that, while compounds 1-3 decompose in a pure aqueous medium, these complexes are very stable in a pH 6 acetate medium. The cyclic voltammetry pattern of each complex is constituted by a first eight-electron reduction wave followed by a second large-current intensity wave. The characteristics of the first waves of the complexes are clearly distinct from those obtained for their lacunary precursor [A-R-SiW9O34]10-, a feature that is due to the Ni centers in the complexes. Such observations of electroactive, stable, and highly nickel-rich polyoxometalates are not common. Measurements of the magnetic susceptibility revealed the occurrence of concomitant ferromagnetic and antiferromagnetic interactions in 1 and 3.For both of these compounds, the extension of the magnetic exchange has been determined by means of a spin Hamiltonian with three and four J constants, respectively.

Properties of a Tunable Multinuclear Nickel Polyoxotungstate Platform

“…Owing to the too close chemical shifts, the two resonances of the phosphate atoms and the phosphonate atoms in NaK-Ni 7 -Ale 2 are suspected to overlap and not resolved enough to be distinguishable. [27,28] UV/Vis spectroscopy and cyclic voltammetry (CV) were used to show that NaK-Ni 7 -Ale 2 and Ni 7 -(AleNapht) 2 are the most stable POMs in aqueous electrolytes. [26] Finally, compound NaNH 4 -Ni 7 -Ale 2 being poorly soluble in solution has been subjected to 31 Electrochemistry and preliminary evaluation towards NO x reduction electrocatalysis: The electrochemistry of high-nuclearity POMs attracts much attention because they are promising candidates for photoelectrocatalysis of multi-electron reactions due to their electron reservoir and/or sink behaviour.…”

“…More specifically, only few examples of electroactive polynuclear Ni II POMs stable in the usual aqueous electrolytes have been reported. [27,28] UV/Vis spectroscopy and cyclic voltammetry (CV) were used to show that NaK-Ni 7 -Ale 2 and Ni 7 -(AleNapht) 2 are the most stable POMs in aqueous electrolytes. Here, we report the electrochemical characterisation of these two POMs in an acetate medium at pH 6.…”

Monomeric, Dimeric Helical, and 1D Nickel Polyoxotungstates Structured by Carboxylate Derivatives

“…[7] Structure of Na 1. 5 8- [8] by formally replacing the three acetato ligands by dimethylaminobutyrate. In 1, three crystallographically equivalent Ni II ions are inserted in the vacancies of the {SiW 9 } polyanion and connected to a fourth Ni II center through the carboxylato groups of three dimethylaminobutyrate molecules and three hydroxido ligands, and the resulting structure has a C 3 axis passing through the capping paramagnetic center and the silicon atom (Figure 1).…”

“…[16] In addition, these results are in perfect agreement with the values determined for the related 15-(J 1 = -37.8 cm -1 , J 2 = +12.0 cm -1 ). [8,17] It can be noticed that no acceptable fit has been obtained by using a model that does not consider isolated [Ni(H 2 O) 6 ] 2+ countercations. The χ M T = f(T) curve of the octanuclear complex 2 can also be fitted with the same coupling model, and this shows that the two {Ni 4 } fragments constituting 2 can be considered magnetically isolated.…”

Dimeric Nickel(II) Containing Tungstogermanate [{β‐GeNi2W10O36(OH)2(H2O)}2]12–

“…[8] POMs with several exchange-coupled paramagnetic metal ions (e. . [13] Here we report on the synthesis, structural characterization, magnetic studies, and X-ray photoelectron spectroscopy of a dimeric tetranickel(II) containing 20-tungsto-2-germanate. 12-(1).…”