Acidity of Carboxylic Acid Ligands Influences the Formation of VO₂(A) and VO₂(B) Nanocrystals under Solvothermal Conditions

Vanadium dioxide (VO2) can adopt many different crystal structures at ambient temperature and pressure, each with different, often desirable, electronic, optical, chemical properties. Understanding how to control which phase forms under various reaction conditions is therefore crucial developing VO2 for applications. This paper describes the impact of ligand acidity on formation nanocrystals from solvothermal vanadyl acetylacetonate (VO(acac)2) stoichiometric amounts water. Carboxylic acids examined herein favor monoclinic VO2(B) over tetragonal VO2(A) as concentration water in increases. However, threshold required obtain phase-pure increases pKa carboxylic acid decreases. We also observe that increasing VO(acac)2 or while keeping constant favors VO2(A). Single-crystal electron diffraction measurements enable identification carboxylate species formed reactions do not contain enough promote VO2. Increasing length carbon chain aliphatic did obtained but result a change nanorod nanoplatelet morphology. These results suggest inhibiting rate hydrolysis precursor either by decreasing ratio fraction molecules are protonated VO2(B).