FULL PAPER DOI: 10.1002/ejic.200800708 A Convenient Mode to Stabilize M I Metal Ions by Using Thiosemicarbazones Alfonso Castiñeiras, [a] Rosa Pedrido,* [a] and Gael Pérez-Alonso [a] Keywords: Thiosemicarbazone ligands / Gold / Luminescence / Heterocycles We investigated the coordinative behaviour of the phosphan- ylthiosemicarbazone ligand 2-[2-(diphenylphosphanyl)- benzylidene]-N-phenylthiosemicarbazone (HLPPh) towards coinage M I metal ions (M = Cu, Ag, Au). The complexes ob- tained, with formulae [Cu(HLPPh) 2 ]Br (1), [Cu(HLPPh) 2 ]I· H 2 O(2), [Ag(HLPPh)(NO 3 )]·3H 2 O(3) and [Au 2 (HLPPh) 2 ]· 3CH 3 OH (4), were satisfactorily characterized by elemental analysis, IR and 1 H/ 31 P NMR spectroscopy as well as ESI mass spectrometry. In addition, we obtained the crystal struc- Introduction Thiosemicarbazone ligands are versatile molecules, not only because of their pharmacological activity, they also give rise to an enormous variety of structures for their metal complexes. [1–6] This versatility arises from the pos- sibility to act as N,S-donor systems, forming stable four and five-membered metallacycles. In addition, the coordination capacity of thiosemicarbazones can be increased by using aldehydes or ketones that contain additional donor func- tional groups in suitable positions for chelation or by using appropriate co-ligands (e.g. phosphanes) for their prepara- tion. On the other hand, the coordination behaviour of thio- semicarbazone ligands towards M I metal ions remains still quite unexplored. The great majority of the cases reported are heteroleptic copper(I) compounds, which contain the M I ion coordinated to the thiosemicarbazone ligand and phosphanes as coligands. Phosphanes have been widely em- ployed as a coordinative strategy to synthesize M I com- plexes with thiosemicarbazones and therefore generating M I heteroleptic complexes. On the contrary there are very limited studies on M I homoleptic thiosemicarbazone com- plexes, which can be defined as metal(I) compounds exclu- sively derived from thiosemicarbazone ligands. The re- ported cases are mainly Cu I and Ag I dinuclear bishelical or tetranuclear cluster compounds formed by spontaneous self assembly processes. [3–7] In contrast, the chemistry of homo- leptic Au I complexes with thiosemicarbazones remains tot- ally unexplored. [a] Departamento de Química Inorgánica, Facultade de Farmacia, Universidad de Santiago de Compostela, Santiago de Compostela, 15782 Spain Fax: +34-981-597-525 E-mail: rosa.pedrido@usc.es © 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Eur. J. Inorg. Chem. 2008, 5106–5111 5106 ture of the complex [Au 2 (μ-S,P-HLPPh) 2 ]Cl 2 (5), which is the first example of a homoleptic thiosemicarbazone Au I com- plex, because the Au I ion has been stabilized by exclusively using a phosphanylthiosemicarbazone ligand. We also per- formed preliminary luminescence studies for these com- plexes, as well as the screening of its biological activity against human cervical carcinoma (HeLa) cells. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) Keeping in view the above observations, we think that the use of phosphanylthiosemicarbazone ligands could be a convenient method to obtain homoleptic M I thiosemicarb- azone complexes. Surprisingly, the coordinative studies with this ligand type are very limited since they were previously employed only to prepare platinum(II) and gold(III) mono- mer species. [7] For that reason, we have decided to use a phosphanylthiosemicarbazone ligand as suitable approach to stabilize homoleptic Cu I , Ag I and Au I complexes. Results and Discussion Chemistry The phosphanylthiosemicarbazone ligand 2-[2-(diphenyl- phosphanyl)benzylidene]- N-phenylthiosemicarbazone (HLPPh, Scheme 1) was prepared as reported before. [8] Re- action of HLPPh with copper(I) bromide and copper(I) io- dide resulted in the formation of the copper(I) complexes, [Cu(HLPPh) 2 ]Br (1) and [Cu(HLPPh) 2 ]I·2H 2 O(2), both containing the corresponding halide atom as counterion. It must be pointed out here that the formation of complexes 1 and 2 occurs instantaneously in the presence of air, with the colour of the solution changing from yellow to orange after the halide salt was added. This fact rules out the Cu I oxidation during the synthesis of these two systems. Never- theless, the copper(I) complexes easily experienced oxi- dation in dmso (bromide and iodide complexes 1 and 2) and in dmf (iodide complex 2). When silver(I) nitrate was treated with the ligand HLPPh, we obtained the yellow so- lid 3, showing a [Ag(HLPPh)(NO 3 )]·3H 2 O stoichiometry, while complex [Au 2 (HLPPh) 2 ]Cl 2 ·3MeOH (4) was isolated when we employed an aqueous H[AuCl 4 ] solution, pre- viously reduced with 2,2'-thiodiethanol. The four com-