Controlling Electron Delocalization in Vanadium‐Based Hybrid Bronzes through Molecular Templation

Abstract

We show that the conductivity of hybrid vanadium bronzes—mixed‐valence organic‐inorganic vanadium oxides—can be tuned over six orders of magnitude through judicious choice of molecular component. By systematically varying the steric profile, charge density, and propensity to hydrogen bond across a series of eight diammonium‐based molecules, we engender multiple distinct motifs of V–O connectivity within the two‐dimensional vanadium oxide layers of a family of bulk crystalline hybrid materials. A combination of single‐crystal and powder X‐ray diffraction analysis, variable‐temperature electrical transport measurements, and a range of spectroscopic methods, including UV‐visible diffuse reflectance, X‐ray photoelectron, and electron paramagnetic resonance are employed to probe how vanadium oxide layer topology correlates with electron localization. Specifically, alkylammonium molecules yield hybrids featuring more corrugated layers that contain V–O tetrahedra as well as a higher ratio of corner‐sharing to edge‐sharing polyhedra and that exhibit highly localized electronic behavior, while alkyl bipyridinium molecules yield more regular layers with polyhedral edge‐sharing that show substantially delocalized electronic behavior. This work allows for the development of design principles based on structure‐property relationships and brings the charge transport capabilities of hybrid vanadium bronzes to more technologically relevant levels.

Replacing Sodium Ions with Protons in Vanadophosphate Glass: Suppression of Electronic Conduction by Local Structural Change around Vanadium Ions

“…In contrast to these glass samples, the 30HO 1/2 –6VO 5/2 –14VO 2 –50PO 5/2 glass reported herein is unusual because it contains numerous VO 6 units whose role is not clearly known. Recently, the electronic conductivity of various hybrid vanadium bronzes was found to vary widely and be extremely sensitive to the atomic configuration around the V atoms and the connectivity of vanadium oxide polyhedra . Therefore, the greatly different role of VO 6 and VO 4 on electrical conduction in glass is highly plausible.…”

“…However, the Raman spectrum did not provide information on the valence state and coordination number of V ions, although some reports have ascertained the coordination number from Raman spectra. Therefore, in the present study, the structures of the glass samples were explored by referring to previously reported 31 P and 51 V nuclear magnetic resonance (NMR) spectra of glass samples with nominal compositions close to that of the 30NaO 47 among these samples, the glass sample with x = 10 is similar in composition to the glass reported herein. According to their report, the phosphate framework comprised Q 2 units with a considerable amount of Q 1 ; notably, their NMR results substantiate the aforementioned explanation of the Raman spectra of the glass investigated herein.…”

“…Recently, the electronic conductivity of various hybrid vanadium bronzes was found to vary widely and be extremely sensitive to the atomic configuration around the V atoms and the connectivity of vanadium oxide polyhedra. 51 Therefore, the greatly different role of VO 6 and VO 4 on electrical conduction in glass is highly plausible. An attempt was made to record the 31 P and 51 V NMR spectra of the glass samples to assess the coordination of V ions; however, the NMR signals could not be obtained owing to the electron spin effect of the V 3d electrons.…”