Preparation of O2XeF2-x(OTeF5)x, OXeF4-y(OTeF5)y and XeF4-y(OTeF5)y (x = 0-2, y = 0-4) and study by xenon-129 and fluorine-19 NMR and Raman spectroscopy: the oxygen primary isotopic effect in the xenon-129 NMR spectra of xenon(VI) oxyfluorides (XeO2F2 and XeOF4) Journal Articles