Spectroscopic aspects of the coordination modes of 2,4-dithiohydantoins: Experimental and theoretical study on copper and nickel complexes of cyclohexanespiro-5-(2,4-dithiohydantoin)

The complexation of cyclohexanespiro-5-(2,4-dithiohydantoin), L, with copper and nickel was studied by means of experimental and theoretical methods. The Cu(I) and Ni(II) complexes were synthesized and characterized using 13C CPMAS NMR, IR and FAB-MS. Reduction of Cu(II) ions and the formation of Cu(I) complexes with dithiohydantoin was proved. Various coordination modes were investigated on the basis of calculated (DFT-GIAO) shielding constants of the free ligand and model structures of the complexes. General trends in the changes of spectroscopic parameters (NMR chemical shifts, vibrational modes) upon different types of coordination were outlined. Dimeric structures for the Cu(I) and Ni(II) complexes were proposed in which the ligands were coordinated in N3^S4- and N3^S2-bridging ways, respectively, acting as monoanions. The results demonstrate that the combined experimental (13C CPMAS NMR, IR) and theoretical (DFT) approach can be used to characterize the molecular structure of solid complexes for which crystallographic data are not available.