Reaction of TaF5 with SMe2 and RS(CH2)(2)SR (R = Me, Et or Pr-i) in anhydrous CH2Cl2 solution produce colourless, extremely moisture sensitive crystals of [TaF4(SMe2)(4)][TaF6] and [TaF4{RS(CH2)(2)SR}(2)][TaF6] respectively, which contain eight-coordinate cations and octahedral anions, whereas TaF5 reacts with neat SR2 (R = Me or Et) to form six-coordinate [TaF5(SR2)]. Very unstable [TaF5(SeMe2)] and [(TaF5)(2){mu-MeSe(CH2)(2)SeMe}] were isolated with the selenoether ligands and also contain six-coordinate tantalum species. Selected complexes of TaCl5 and TaBr5 have been prepared for comparison. The complexes have been characterised by IR, UV/visible and H-1 and F-19{H-1} NMR spectroscopies, and X-ray crystal structures are reported for [TaF4{MeS(CH2)(2)SMe}(2)][TaF6], [(TaCl5)(2){mu-MeSe(CH2)(2)SeMe}] and [TaCl5(SeMe2)]. O 2012 Elsevier B.V. All rights reserved.