Interactions of a beta-dipeptide with monovalent metal cations: crystal structures of (anthranoyl)anthranilic acid and its lithium, sodium and thallium salts.
X-ray crystal structure analyses have been performed on the beta-dipeptide (anthranoyl)anthranilic acid [HAnthAnthOH] and its lithium, sodium and thallium salts [HAnthAnthOM] to give a first set of data for this representative model ligand. Crystals of the beta-dipeptide are orthorhombic, space group Pca2(1). The unit cell contains two molecules of (anthranoyl)anthranilic acid which form a dimer via hydrogen bonds. The components of the beta-dipeptide are rotated into the trans-conformation which allows for internal hydrogen bonds. The pKS value of (anthranoyl)anthranilic acid (9.80+/-0.14) shows a slight decrease as compared to anthranilic acid; the metal salts can therefore be prepared by direct neutralization of the beta-dipeptide with metal hydroxides or carbonates. The alkali compounds crystallize as the trihydrates [HAnthAnthOM(H2O)3, M=Li, Na] in the triclinic space group p1. Both metal ions show a clear preference for water molecules over the (anthranoyl)anthranilate anions as ligands in their coordination spheres. As a consequence, the [HAnthAnthO]- anions are only partially involved in metal complexation. The cell plots of both compounds exhibit a stacking with an alternation of oppositely charged layers. The negatively charged layers are composed exclusively of (anthranoyl)anthranilate anions. The thallium compound crystallizes as the hemihydrate [HAnthAnthOTl(H2O)0.5] in the monoclinic space group C2/c. In the dinuclear units, the thallium ions accommodate one nitrogen and four oxygen atoms of the anions in their coordination sphere and in addition entertain weak Tl-arene contacts. In contrast to the alkali compounds, the water molecules are not involved in metal complexation, but contribute to a network of hydrogen bonding.
Wiesbrock
Frank
F
Anorganisch-chemisches Institut, Technische Universität München, Lichtenbergstrasse 4, D-85747 Garching, Germany.
Schmidbaur
Hubert
H
D002414:Cations, Monovalent / Q000737:chemistry; D018360:Crystallography, X-Ray / Q000379:methods; D004151:Dipeptides / Q000737:chemistry*; D006860:Hydrogen Bonding; D008094:Lithium / Q000737:chemistry; D008670:Metals / Q000737:chemistry*; D015394:Molecular Structure; D011487:Protein Conformation; D012964:Sodium / Q000737:chemistry; D013793:Thallium / Q000737:chemistry; D062367:ortho-Aminobenzoates / Q000737:chemistry*
D002414:Cations, Monovalent; D004151:Dipeptides; D008670:Metals; D062367:ortho-Aminobenzoates; D008094:Lithium; D012964:Sodium; D013793:Thallium