Dalton Transactions PAPER Cite this: DOI: 10.1039/c8dt00848e Received 5th March 2018, Accepted 13th April 2018 DOI: 10.1039/c8dt00848e rsc.li/dalton Reductive transformation of V(III) precursors into vanadium(II) oxide nanowires† Olusola Ojelere, David Graf, Tim Ludwig, Nicholas Vogt, Axel Klein and Sanjay Mathur * Vanadium(II) oxide nanostructures are promising materials for supercapacitors and electrocatalysis because of their excellent electrochemical properties and high surface area. In this study, new homoleptic vanadium(III) complexes with bi-dentate O,N-chelating heteroarylalkenol ligands (DmoxCHvCOCF 3 , PyCHvCOCF 3 and PyNvCOCF 3 ) were synthesized and successfully transformed by reductive conversion into VO nanowires. The chemical identity of V(III) complexes and their redox behaviour were unambigu- ously established by single crystal X-ray diffraction studies, cyclic voltammetry, spectrometric studies and DFT calculations. Transformation into the metastable VO phase was verified by powder X-ray diffraction and thermo-gravimetry. Transmission electron microscopy and X-ray photoelectron spectroscopy data confirmed the morphology and chemical composition of VO nanostructures, respectively. Introduction The long-standing interest in vanadium oxide chemistry has been due to its relevance to several industrial processes as well as its unique redox chemistry. 1 The redox activity and layered structures of crystalline vanadium oxides make these materials useful as intercalation cathodes for Li-ion batteries. 2,3 Vanadium oxides have also been applied in catalytic and electrochemical fields due to their outstanding structural and valence flexibility. 4,5 Currently, the search for different poly- morphs of vanadium oxides that possess electrically induced valence switching properties is advancing rapidly due to their potential in heterogeneous catalysis and energy storage materials. 6,7 Several vanadium oxides show interesting properties in energy generation and conservation such as smart window for energy savings, 8,9 cathode materials for Li-ion batteries 10 and perovskite solar cells. 11 Vanadium monoxide (VO) represents a metastable phase in the V–O binary phase diagram that is interesting because of its unique redox chemistry and satisfac- tory electrical conductivity due to its partially filled conduction band. 12 Nevertheless, a reproducible synthesis of VO is chal- lenging due to the coexistence of a large number of poly- morphs of vanadium oxides 13 (Fig. 1, ref. 14 and 15). Nanostructured vanadium oxides have been obtained by sol–gel, 16 pyrolysis, 17 hydrothermal methods, 18 chemical vapor deposition, 19 electrospinning 20 and thermal reduction in the presence of a catalyst. 21 However, reports on the controlled synthesis of vanadium(II) oxide nanomaterials especially from molecular precursors are still unexplored to a larger extent mainly due to the unavailability of suitable vanadium precursors and thermodynamic instability of the vanadium(II) oxide. Our research group has recently reported on the synthesis of volatile complexes from transition and main group metals using substi- tuted heteroarylalkenol ligands, which offer a stabilizing effect by building six-membered metallacycles upon coordination to the central atom, which can also influence the physico-chemical Fig. 1 Schematic vanadium–oxygen phase diagram based on the experimental data from Wriedt and the calculated data from Kang. 14,15 The Magnélie phases V n O 2n-1 are highlighted in blue and the Wadsley phases V n O 5n-2 in green. † Electronic supplementary information (ESI) available. CCDC 1827585–1827587. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c8dt00848e Institute of Inorganic Chemistry, University of Cologne, Greinstraße 6, D-50939 Cologne, Germany. E-mail: sanjay.mathur@uni-koeln.de This journal is © The Royal Society of Chemistry 2018 Dalton Trans. Published on 14 April 2018. Downloaded by University of Cologne on 04/05/2018 14:40:15. View Article Online View Journal