Synthesis, Structures, and Crystalline Packing Features of [Co(tren)(amino acidato-N,O)]X2·nH2O (X = ClO4−, I−)

The crystal structures of several novel compounds, trans(N,t-N) isomers of [Co(tren)(DL-phenylalaninato)](ClO4)2 (1), [Co(tren)(L-phenylalaninato)]I2 · H2O (2), [Co(tren)(L-prolinato)]I2 · H2O (3), [Co(tren)(L-tryptophanato)](ClO4)2·1/2H2O (4), [Co(tren)(L-valinato)]I2·1/3H2O (5), [Co(tren)(L-isoleucinato)]I2 (6), and [Co(tren)(L-leucinato)]I2 (7), have been determined. Their packing arrangements indicate that the complex cations in all of the compounds form helical strings running along their crystallographic axes, for both chiral and racemic amino acidato species. Intermolecular double and single hydrogen bonds are formed by the carbonyl oxygens and amino hydrogens of the tren ligand or of the amino acidato moiety, either directly or by the assistance of water molecules of hydration. In this fashion, [Co(tren)(amino acidato-N,O)]2+ is strung together into helical arrays. In the racemic compounds, the complex cations of different strings have opposite chirality. Phenylalanine is racemized during the coordination process, under mild pH (7.5−8.0) and temperature (60 °C). This is quite unusual. Finally, 1D and 2D (COSY) 1H NMR spectra were recorded, in which compound 4 shows interesting cross-peak correlations between the phenyl protons and amino protons.