NbCl4 reacts with the dithioethers MeS(CH2)nSMe (n = 2 or 3), iPrS(CH2)2SiPr or o-C6H4(CH2SEt)2 in a 1 : 1 molar ratio in CH2Cl2 or toluene over several days, to give red or orange, paramagnetic complexes, [NbCl4(dithioether)]. Their X-ray crystal structures confirm distorted octahedral geometries with chelating dithioether. MeS(CH2)2SMe, alone, also forms an [NbCl4{MeS(CH2)2SMe}2] complex based upon eight-coordinate Nb(iv) in a square antiprismatic geometry. Similar six-coordinate cis-[NbCl4(diselenoether)] are formed by MeSe(CH2)nSeMe (n = 2 or 3) and nBuSe(CH2)3SenBu. The monodentate ligands Me2S, Me2Se and nBu2Se form [NbCl4(R2E)2] (E = S, Se) which are unstable in solution, losing R2E to form complexes with a 1 : 1 stoichiometry, which are shown to be diamagnetic dimers, [(Me2E)Cl3Nb(μ-Cl)2NbCl3(Me2E)], with single Nb-Nb σ-bonds. Tellurium ligands tend to decompose in these reactions, but reaction at room temperature of Me2Te and NbCl4 formed [NbCl4(Me2Te)2], the X-ray structure of which revealed an eight-coordinate dimer, [Nb2Cl4(μ-Cl)4(Me2Te)4]. The new complexes have been characterised by microanalysis, IR, UV-visible spectroscopy and magnetic measurements. X-ray crystal structures are reported for [NbCl4(L-L)] (L-L = MeS(CH2)nSMe, n = 2 or 3, iPrS(CH2)2SiPr, o-C6H4(CH2SEt)2, MeSe(CH2)3SeMe), [Nb2Cl8(Me2Te)4], [Nb2Cl8(Me2S)2] and [Nb2Cl8(Me2Se)2]. The complexes are very sensitive to moisture and dioxygen, and some also readily undergo C-E bond cleavage. Two ligand fragmentation products were identified -[Nb2Cl4(μ-S)2{MeS(CH2)3SMe}2] and [Nb2Cl4(μ-Se)2{o-C6H4(CH2)2Se}4]. X-ray crystal structures are also reported for the oxidation/hydrolysis products [NbOCl3(Me2S)] and [NbOCl3{MeS(CH2)2SMe}].