Lithium complexes of neutral and anionic glycine (GlyH) and glycylglycine (diglycine; GlyGlyH) have been prepared. They were crystallized from water or water/alcohol mixtures in the form of [Li(GlyH)(H 2O)] +Cl − ( 1), Li +Gly − ( 2), [Li(GlyGlyH)] +Cl − ( 3) and Li +GlyGly −·1H 2O ( 5). The complexation of Li + by the amino acids and dipeptides is accompanied by characteristic low field shifts of their 13C NMR resonances but details about the coordination modes are only available from solid-state structure determinations (1: C 2H 7ClLiNO 3, monoclinic, space group P2 1/ c (No. 14), a=10.103(2), b=5.064(1), c=11.930(2) Å, β=107.39(1)°, V=582.46 Å 3, Z=4, R w=0.059; 2: 2: C 2H 4LiNO 2, orthorhombic, space group P2 12 12 1 (No. 19), a=4.998(1), b=7.864(1), c=9.261(1) Å, V=364.0 Å 3, Z=4, R w,=0.054; 3: C 4H 8ClLiN 2O 3, triclinic, P 1 (No. 2), a=5.033(1), b=7.533(1), c=10.132(2) Å, α=76.54(1), β=88.42(1), γ=84.56(1)°, V=371.9 Å 3, Z=2, R w=0.030; 5: C 4H 9LiN 2O 4, monoclinic, space group P2 1 (No. 4), a=7.290(1), b=4.923(1), c=10.431(1) Å, β=101.73(1)°, V=366.5 Å 3, Z=2, R w=0.034). The structure of 3 is isotypic with the previously described Br − salt [Li(GlyGlyH)] +Br − (R. Meulemans, P. Piret and M. van Meersche, Bull. Soc. Chim. Belg., 80 (1971) 73). In all four complexes the Li + cation is tetrahedrally four- coordinate. Three of the coordination sites are occupied by carboxylate oxygen atoms from three different but crystallographically equivalent glycine or diglycine molecules, respectively. The fourth coordination site at Li + is different in each complex. In 1 the lithium coordination sphere is completed by a water molecule, in 2 the (deprotonated) amino group of the amino acid acts as additional donor, while in 3 and 5 the keto oxygen atom of the peptide bond is Li +-coordinated. Quite remarkably, in 5 neither the deprotonated −NH 2 group not the cocrystallized water molecule effectively compete for Li + coordination but are only engaged in an intricate net of hydrogen bonding interactions. On the basis of these results the following sequence of donor atom strength towards Li + may be established for these ligands: −COO −≈C(O)>−NH 2>H 2O. Further weight is given to this conclusion by the fact that the Li + coordination to the carboxylate groups is identical in all four complexes: one of their oxygen atoms bridges two Li + cations while the second one is coordinated to a single third Li +. The lithium coordination has drastic effects on the conformation of the peptide backbone in the dipeptides in 3 and 5. They are different from each other as well as from that of uncomplexed diglycine in the solid state.