New chemistry with old ligands:: N-alkyl- and N,N-dialkyl-N′-acyl(aroyl)thioureas in co-ordination, analytical and process chemistry of the platinum group metals

Recent developments in the fundamental co-ordination chemistry of N-alkyl-N '- (H2L) and N,N-alkyl-N ' -acyl(aroyl)thioureas (HL) of Pt(II), Pd(II) and Rh(III) are reviewed. These studies show that the mode of co-ordination of H,L differs markedly from that of HL, the former ligand generally co-ordinating through the sulphur donor atom to Pt(II) and Pd(II), mimicking the co-ordination of simple thioureas, while HL tends to co-ordinate in a cis bidentate S,O manner to d(8) metal ions, with loss of a proton. A series of new, relatively hydrophilic N-alkyl-N '- and NN-alkyl-N ' -acylthioureas have been prepared, and their co-ordination chemistry investigated. The new ligand, N-propyl-N ' -butanoylthiourea (H2L8) shows an unprecedented N ' ,S mode of co-ordination of Pt(II) to yield trans-[Pt(HL8-N,S)(2)]. Moreover, the favourable physiochemical properties of Pt(II), Pd(II) and Rh(III) complexes makes these ligands useful for the reversed-phase HPLC determination of traces of these metal ions in real effluent streams, following complex formation in a homogeneous acetonitrile-hydrochloric acid phase and subsequent salt-induced phase separation. Complexes prepared in situ of Pt(II), Pd(II) and Rh(III) with N,N-di(2-hydroxylethyl)-N ' -benzoylthiourea can quantitatively be pre-concentrated onto thin film C-18-modified glass-fibre disks, followed by quantification using laser ablation inductively coupled mass spectroscopy at trace levels. Preliminary results show this method to be applicable to untreated PGM refinery process effluents. (C) 2001 Elsevier Science B.V. All rights reserved.