A Supramolecular Tetradecanuclear Copper(II) Polyoxotungstate

Abstract

Polyoxometalates (POMs) can be perceived as discrete fragments of extended metal oxide lattices.[1] They continue to attract much attention with respect to their widespread applications.[ , V IV,V ) respectively. These species are diamagnetic when the metals M are in their highest oxidation state. Mono, di and trivacant species of the Keggin type polyoxotungstates can be easily prepared, [3] and then act as nucleophilic ligands for transition-metal (TM) or rare-earth cations. Such inclusions can then lead to the formation of magnetic clusters. Trivacant POMs are the best candidates to obtain compounds with the largest number of interacting magnetic cations. Recently, compounds with a number (from one to nine) of paramagnetic TM centers of the first row ranging were reported.[

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

“…Due to the disorder, it has not been possible to support the presence of the protons by bond valence sum calculations, but the charge stated for the {b-SiW 8 O 31 } fragment in 2 does agree with that found for the same subunit in the complexes 1 and 1 a. The presence of a supplementary Co II ion capping this Keggin unit indicates, as postulated by Kortz et al, [20] that it is possible to connect additional metallic atoms to the surface of the {b-SiW 8 O 31 } group after filling its vacancies, highlighting the basicity of this fragment. Interestingly, it is the first time that such a triangular {Co 3 …”

“…In the case of 2, potassium cyanate was added to the reacting medium. The decomposition of the precursor into the {B-b-SiW 9 O 34 } and {b-SiW 8 O 31 } units has been observed and discussed previously. [10,20,21] The {(B-b-SiW 9 O 33 (OH))(bSiW 8 O 29 (OH) 2 )Co 3 A C H T U N G T R E N N U N G (H 2 O)} unit can be obtained under various reaction conditions (medium, temperature, concentration), [20] highlighting the stability of this sandwich polyoxometalate entity.…”

“…(1) consists of two {(B-b-Si-W 9 O 33 (OH))(b-SiW 8 O 29 7 ]·36 H 2 O (2), a {g-SiW 10 (q av(Co-L-Co) = 99.18) than in 1 (q av(Co-LCo) = 92.88). Weaker ferromagnetic interactions were found in 2 than in 1, in agreement with larger Co-L-Co angles in 2.…”

“…This is generally achieved by acid-base condensation, [7] but supramolecular assemblies around small anions such as halides can also be effective. [8] Recently, insertion into paramagnetic polyoxometalate matrices of exogenous ligands and especially that of the azido anion [9] has shown that such polydentate ligands can also allow the assembly of magnetic polyoxometalate subunits, [10] but in addition could impose ferromagnetic interactions within the cluster. [11,12] Co II polyoxometalate compounds containing from two to nine interacting paramagnetic centers have been reported.…”

A Nonanuclear Copper(II) Polyoxometalate Assembled Around a μ‐1,1,1,3,3,3‐Azido Ligand and Its Parent Tetranuclear Complex

“…[14] Nevertheless, the structure of this complex could not be obtained by Xray diffraction. When this compound was dissolved in a molar NaCl solution, large crystals of the azido-free supramolecular complex [{(SiW 9 O 34 )(SiW 9 O 33 (OH))(Cu-(OH)) 6 Cu} 2 Cl] (denoted {Cu 14 }) were obtained within minutes.…”