Synthesis of a highly reactive form of WO2Cl2, its conversion into nanocrystalline mono-hydrated WO3 and coordination compounds with tetramethylurea

Abstract

A new form of WO₂Cl₂ was obtained by modification of a literature procedure. Both the newly prepared WO₂Cl₂ and the commercial yellow WO₂Cl₂ exhibited an orthorhombic structure (powder X-ray diffraction, P-XRD), and their air exposure at room temperature afforded light green and lemon yellow WO₃·H₂O (orthorhombic phase), respectively. These materials were characterized by P-XRD, high-resolution transmission electron microscopy (HR-TEM) and scanning transmission electron microscopy (S-TEM). The analyses revealed the nanocrystalline nature of light green WO₃·H₂O, and the prevalent amorphism of lemon yellow WO₃·H₂O. The reactions of grey WO₂Cl₂ with one and two equivalents of tetramethylurea (tmu), in CH₂Cl₂ at room temperature, led to the isolation of the trinuclear complex [WO₂Cl₂(tmu)]₃, 1 (45% yield), and the mononuclear one WO₂Cl₂(tmu)₂, 2 (64%), respectively. Compounds 1 and 2 were fully characterized by analytical and spectroscopic methods, single crystal X-ray diffraction (SC-XRD) and DFT calculations.