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) an d Rh(III) are reviewed. These studies show that the mode of co-ordination o f H,L differs markedly from that of HL, the former ligand generally co-ordi nating through the sulphur donor atom to Pt(II) and Pd(II), mimicking the c o-ordination of simple thioureas, while HL tends to co-ordinate in a cis bi dentate S,O manner to d(8) metal ions, with loss of a proton. A series of n ew, relatively hydrophilic N-alkyl-N '- and NN-alkyl-N ' -acylthioureas hav e been prepared, and their co-ordination chemistry investigated. The new li gand, N-propyl-N ' -butanoylthiourea (H2L8) shows an unprecedented N ' ,S m ode of co-ordination of Pt(II) to yield trans-[Pt(HL8-N,S)(2)]. Moreover, t he favourable physiochemical properties of Pt(II), Pd(II) and Rh(III) compl exes makes these ligands useful for the reversed-phase HPLC determination o f traces of these metal ions in real effluent streams, following complex fo rmation in a homogeneous acetonitrile-hydrochloric acid phase and subsequen t salt-induced phase separation. Complexes prepared in situ of Pt(II), Pd(I I) and Rh(III) with N,N-di(2-hydroxylethyl)-N ' -benzoylthiourea can quanti tatively 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 ap plicable to untreated PGM refinery process effluents. (C) 2001 Elsevier Sci ence B.V. All rights reserved.