MATERIALS AND METHODS lSC-NMR spectra were taken on a JEOL-CX-100 (Japan) apparatus, at a working frequency of 25 MHz. Chemical shifts were determined using DMSO- d 6 as an internal standard. Infrared spectra were obtained using a Specord IR-75 (GDR) spectrometer, in KBr tablets. The experimentally determined elemental analyses agree with calculated compositions.