Aromatic C-H---S interaction in the arenethiolate complexes of cadmium(II)with S2N2 donor set evidenced from Cd-113 NMR spectroscopy

Cd-113 NMR spectroscopy was employed to investigate the interactions betwee n aromatic C-H and the coordinated sulfur atom in the neutral four-coordina ted cadmium(Il) complexes, [Cd{S-2-(4-X-C6H4CONH)C6H4}(2)(1-MeIm)(2)] (X = H, OMe, F and CN; 1-MeIm = 1-methylimidazole). The coordinating atom set he re is S2N2 that is similar to the zinc and iron sites in the known metallop roteins such as zinc finger and ferredoxins, respectively. The observation of Cd-113 NMR signals in the range 480-420 ppm in chloroform at 298 K indic ates that the cadmium(II) ion is bound with the S2N2 donor set in solution. The complex without substituent (i.e. X = H) exhibits a Cd-113 NMR signal at 475 ppm while the analog with the strongest electron-withdrawing cyano s ubstituent gives a signal at 424 ppm in chloroform at 298 K. The chemical s hifts of cadmium(II) complexes with a variety of substituents had a linear correlation with the Hammett sigma(m) values rather than the sigma(p) value s, although the substituents are at the para-position of the benzoyl group. The results demonstrate that there an aromatic C-H---S interactions betwee n the protons of the benzoyl group and the coordinated sulfur atom in the c admium(II) complexes with S2N2 binding site, in addition to the NH---S hydr ogen bonds which were confirmed by infrared and H-1 NMR spectroscopies. (C) 1999 Elsevier Science Inc. All rights reserved.