Chelates of Ge(II) and Sn(II) Symmetrically and unsymmetrically substituted germane- and stannanediyls as well as chelated bis(amino)- or aminooxogermanium- and -tinmonohalides have been obtained from cyclic bis(amino)germane- and stannanediyls by treatment with tert-butylamine, tert-butanol and tert-butylmercaptane. The following compounds have been synthesized: GeX 2 (X = OtBu (5), StBu (6)), Sn(StBu), (9), GeXCl (X = N(H)tBu (21), OtBu (22)), SnXCl (X = N(H)tBu (23), OtBu (24), StBu (25), OMe (28)) and Sn(OtBu)Br (27). In the series of the chelates Me 2 Si(NtBu)(NHtBu)GeCl (13), Me 2 Si(NtBu)(OtBu)SnX (X = Cl (18), OMe (19)) and the bischelate [Me 2 Si(NtBu)(OtBu)] 2 Sn (20) have been prepared. When 18 is allowed to react with aluminiumtrimethyl Me 2 Si(NtBu)(OtBu)AlClMe is formed, a compound with a center of chirality at the aluminium atom. X-ray structure determinations have been performed on single crystals of 6, 8, 9, 13, 22 and 24. 6, 8, 22 and 24 form molecular dimers with c.n. of 3 at the Ge or Sn atoms, resp. While the tBu-S ligands are syn with respect to the central Ge 2 S 2 ring in 6 (symmetry approaching C 2v ), the tBu-O ligands are anti to the central Sn 2 O 2 ring in 8 (symmetry C i ). 9 forms a coordination polymer with all Sn atoms in a Ψ-trigonal-bipyramidal and all S atoms in a Ψ-tetrahedral environment. The germanium atom in 13 is coordinated by a chlorine, a λ 3 - and a λ 4 -nitrogen atom, the two nitrogen atoms being connected by as dimethylsilyl group. The hydrogen and chlorine atom of 13 are found at the same side of the four-membered chelate ring. The two unsymmetrically substituted, homologous compounds Ge(O/tBu)Cl (22) and Sn(OtBu)Cl (24) are found to form dimers via O→Ge resp. O→Sn bonds. While the chlorine atoms in 22 are syn with respect to the four-membered ring, they are anti in the case of molecule 24.