Six- and eight-coordinate thio- and seleno-ether complexes of NbF5 and some comparisons with NbCl5 and NbBr5 adducts.

The reaction of RS(CH(2))(2)SR (R = Me, Et or (i)Pr) with NbF(5) produces [NbF(4){RS(CH(2))(2)SR}(2)][NbF(6)] which contain distorted eight-coordinate (dodecahedral) cations and octahedral anions, whereas RSe(CH(2))(2)SeR (R = Me or Bu(n)) form six-coordinate [(NbF(5))(2)(mu-RSe(CH(2))(2)SeR)]. Et(2)S and Me(2)Se (L) also form six-coordinate [NbF(5)(L)], but Me(2)S forms both [NbF(5)(Me(2)S)] and an eight-coordinate cation in [NbF(4)(Me(2)S)(4)][NbF(6)]. MeS(CH(2))(2)SMe forms eight-coordinate cations in [NbX(4){MeS(CH(2))(2)SMe}(2)][NbX(6)] (X = Cl or Br), but other complexes of the heavier halides including [NbX(5)(L)] and [(NbX(5))(2)(mu-L-L)] (L-L = RSe(CH(2))(2)SeR; o-C(6)H(4)(CH(2)SMe)(2) and o-C(6)H(4)(CH(2)SeMe)(2)) contain six-coordinate niobium. The very unstable [NbCl(5)(Me(2)Te)] was characterised spectroscopically, but all other attempts to form telluroether complexes resulted in decomposition, and NbI(5) was reduced even by thioethers. The complexes have been characterised by multinuclear NMR ((1)H, (19)F, (93)Nb, (77)Se or (125)Te), IR and UV/visible spectroscopy, and X-ray crystal structures are reported for [NbF(4){RS(CH(2))(2)SR}(2)][NbF(6)] (R = Me, (i)Pr), [NbF(4)(Me(2)S)(4)][NbF(6)], [NbCl(5)(Me(2)Se)], [NbBr(5)(Me(2)S)], [(NbCl(5))(2){o-C(6)H(4)(CH(2)SMe)(2)}] and [(NbCl(5))(2){MeSe(CH(2))(2)SeMe}]. All the complexes are very moisture sensitive and the fluoride complexes decompose slowly with fluorination of the neutral ligand.