Inter-cluster distance dependence of electrical properties in single crystals of a mixed-valence polyoxometalate

Abstract

The electrical conductivity of mixed-valence [MoMoO(SO)] tetraalkylammonium salts was investigated through dependence on the inter-cluster distance that is controlled by tetraethylammonium, tetrapropylammonium, and tetrabutylammonium cations. The crystallographic analysis of single crystals revealed that the inter-cluster distances are dependent on the chain length of the alkyl groups on the counter cations. In addition, the electrical conductivities of the single crystals were found to be dependent on both temperature and chain length. Mixed-valence polyoxometalate (POM) clusters are considered to be a molecular particle of Mo bronze by which highly ordered networks will be developed using single crystals, where POMs are rather small and have a well-organized structure compared to colloidal nanostructures.

Transformation of Polyoxometalate into 3D Porous Li‐Containing Oxide: A Case Study of γ‐LiV2O5 for High‐Performance Cathodes of Li‐Ion Batteries

“…Unfortunately, POM‐based electrode materials suffer badly from inherent drawbacks, including poor intrinsic electronic conductivity, dissolution in the electrolyte, and low voltage plateaus. To overcome the negligible electronic conductivity of POMs (e.g., 10 −11 S cm −1 for [( n ‐C 4 H 9 ) 4 N] 3 [PMo 12 O 40 ] and 8.99 × 10 −13 S cm −1 for [( n ‐C 4 H 9 ) 4 N] 5 H[Mo 18 O 54 (SO 3 ) 2 ]), the strategy of compositing POMs with high conductive substrates, such as carbon nanotubes, graphene, and conductive polymers, was developed . However, ≈70 wt% of conductive additives (including conductive substrates and carbon black) was generally needed to prepare the POM‐based cathodes, which greatly reduced the energy density of electrode materials and sacrificed the high‐capacity advantage of POM compounds.…”

Supramolecular assemblies of organo-functionalised hybrid polyoxometalates: from functional building blocks to hierarchical nanomaterials

“…Furthermore, although POMs have very well-established (and highly tuneable) multi-redox activitiesmarking them as being of considerable interest as unique energy storage, electronic or catalytic species -POMs often exhibit low or negligible conductivity in the solid state. [263][264][265] Consequently, unless processed as thin films or embedded in a conductive matrix (e.g. conductive polymers or bulk or nanostructured carbons, etc.…”

Polyoxometalates-Functionalized Electrodes for (Photo)Electrocatalytic Applications: Recent Advances and Prospects

“…So far, only few investigations have been engaged to study the electron-transport properties in the solid state and to improve their electrical conductivity. A systematic investigation of the charge-transport properties of [S 2 Mo V 2 Mo VI 16 O 60 ] 6– tetraalkylammonium salts [(C n H 2 n +1 ) 4 N] + with various alkyl chain lengths ( n = 2, 3, and 4) has revealed the electrical conductivity followed an Arrhenius-type behavior and decreased with increasing alkyl chain length of tetraalkylammonium (from ∼10 –8 S cm –1 for n = 2 to ∼10 –12 S cm –1 for n = 4, at 300 K), suggesting the electron mobility in the solid state is facilitated by shortening the inter-POMs distances . Coordination assemblies of Preyssler anions bridged with transition metal cations lead to tunable, redox-active metal oxide frameworks with intrinsic conductivity seemingly to be controlled by the nature of the bridging metal.…”