Static vapour pressures are reported for the barium β-diketonate polyether adducts Ba(hfac) 2· (tetraglyme) and Ba(hfac) 2· (18-crown-6), which are important as precursors in chemical vapour deposition (hfac = 1,1,1,5,5,5-hexafluoropentane-2,4-dionato, (CF 3COCHCOCCF 3) −, tetraglyme = 2,5,8,11,14-pentaoxapentadecane, CH 3O (CH 2CH 2O) 4CH 3, 18-crown-6 = 1,4,7,10,13,16-hexaoxacyclooctadecane, c-(CH 2CH 2O) 6). The thermal behaviour of the compounds was also investigated by d.s.c., elemental analysis, and visual observations. Under moderately fast heating, Ba(hfac) 2· (tetraglyme) melts without significant decomposition at the temperature T≈ 428 K. However, the compound may melt during prolonged heating at considerably lower temperatures because of the formation of trace impurities. The molar enthalpy of fusion was measured as (34.8 ± 0.5) kJ·mol −1. Vapour pressures for molten Ba(hfac) 2· (tetraglyme) in the temperature range 401 K to 447 K were fitted to the equation: 1g ( p/Pa) = 13.69 − 5318 ( T/K) −1, consistent with a value of (101.8 ± 1.2) kJ·mol −1for the average molar enthalpy of vaporisation. Ba(hfac) 2· (18-crown-6) samples melted with decomposition only at T> ≈ 533 K. This compound undergoes a solid-state phase transition, study of which is complicated by slow kinetics. Conversion of the low-temperature form to the high-temperature form was demonstrated at temperatures as low as 423 K, and is accompanied by a molar enthalpy change of (16.7 ± 0.3) kJ·mol −1. Vapour pressures for solid Ba(hfac) 2· (18-crown-6) in the temperature range 412 K to 468 K were fitted to the equation: 1g ( p/Pa) = 12.82 − 5480 ( T/K) −1, consistent with a value of (104.9 ± 1.3) kJ·mol −1for the average molar enthalpy of sublimation.