Antibiotics as ligands. Coordination behaviour of cycloserine towards cobalt (II), nickel (II), zinc (II), cadmium (II) and mercury (II) halides

The complexes of cycloserine, 4-amino-3-isoxazolidone, (Ccs) with cobalt(II), nickel(II), zinc(II), cadmium(II), and mercury(II) halides have been synthetized. Their structures have been assigned on the basis of analytical, conductivity, spectral (visible, i.r. and far-i.r.) and magnetic data. The ligand behaves as monodentate O-bonded. The position and multiplicity of the metal-halide stretching frequencies are discussed and used as a guide to the stereochemistry. The most convincing structural evidence for the cobalt derivatives is a predominantly planar environment for the chloro-complex with terminal ligands and terminal halides, while for the 1:3 complexes we could suggest a pentacoordinate structure with terminal both ligands and halides. The nickel(II) chloro- and bromo-derivatives seem to have a pseudo-tetrahedral symmetry, while the iodo-complex resulted pentacoordinate. Both the cobalt(II) and nickel(II) derivatives resulted high spin, with the exception of Co(Ccs)2Cl2. Tetrahedral monomeric and dimeric structures with bridging halide atoms, and pentacoordinate geometries are present in the zinc(II), cadmium(II), and mercury(II) complexes. The water resulted always uncoordinated lattice water. Assignments for the electronic spectra are proposed for all the above reported symmetries; the assignments for the metalligand and metal-halides stretching modes have also been made. We have never observed a metalinduced ring opening under the present experimental conditions.