FULL PAPER A Trinuclear Palladium(II) Complex with Bridging 2-Hydroxyacetophenone N 4 -Ethylthiosemicarbazone Ligands  An Unusual Dimethylformamide Promoted Deprotonation and Aggregation Dimitra Kovala-Demertzi* a , Nikolaos Kourkoumelis a , Douglas X. West b , Jesu ´s Valde ´s-Martı ´nez c , and Simon Herna ´ndez-Ortega c Department of Chemistry, University of Ioannina a , 45110 Ioannina, Greece E-mail: dkovala@cc.uoi.gr Department of Chemistry, Illinois State University b , Normal, IL 61790-4160, USA Instituto de Quı ´mica, Universidad Nacional Autonoma de Mexico c , Circuito Exterior, Ciudad Universitaria, Coyoaca ´n 04510, Me ´xico DF Received August 8, 1997 Keywords: Trinuclear triangulo palladium complex / 2-Hydroxyacetophenone N 4 -ethylthiosemicarbazone / Dimethylformamide aggregation The X-ray crystal structure of a palladium(II) complex of 2- hydroxyacetophenone N 4 -ethylthiosemicarbazone (H 2 Ap4E) shows it to be a triangular, trinuclear complex with bridging thiosemicarbazonato sulfur atoms. This species can be for- Thiosemicarbazones of aromatic ortho-hydroxy aldehydes and ketones have recently attracted considerable attention because of their potential biological properties [1] and cata- lytic activity [2] . These aromatic thiosemicarbazones most often coordinate as the dianion on loss of the phenoxy hy- drogen and thiosemicarbazone moiety's to form mononu- clear [M(ONS)X] (ONS represents the dianionic thiose- icarbazone ligand coordinated via the phenoxy oxygen, azomethine nitrogen and thiolato sulfur and X represents a neutral molecule such as ammonia or pyridine) [3] , or di- nuclear [M(ONS)] 2 {M=Ni(II) or Cu(II) and M-O,O-M bridging pattern} [4] [5] [6] [7] have been isolated on depro- tonation of the ring hydroxy group and loss of the N(2) hydrogen of the thiosemicarbazone (tsc) moiety. Most re- cently, a trinuclear nickel(II) complex with both Ni-O,O-Ni and Ni-S,O-Ni bridging patterns has been reported [8] . Two monomers combine to form a butterfly- shaped dimer by Ni-O,O-Ni bonding and a third mono- mer binds to the dimer via Ni-S,O-Ni bridging. Pal- ladium(II) complexes of tscs of 2-acetylpyridine have been studied with regard to their structural and biological properties, and some of them show remarkable antitumour activity [9] [10] [11] . Therefore, we expanded our studies of pal- ladium(II) complexes to include other potentially tridentate tsc ligands and report here the structure of [Pd(Ap4E)] 3 ·DMF (Ap4E is the dianion of 2-hydroxyace- tophenone N 4 -ethylthiosemicarbazone) with Pd-S-Pd bridging. Eur. J. Inorg. Chem. 1998, 861-863  WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1998 1434-1948/98/0606-0861 $ 17.50+.50/0 861 med from a monomer on dissolution in DMF or directly from Li 2 PdCl 4 and the thiosemicarbazone in methanol-ammonia solution. Although numerous dinuclear palladium complexes are known, only a few trinuclear palladium complexes have been reported [12] [13] . Triangular complexes [12] [13] , as well as linear complexes [14] , have been structurally characterized. Linear tripalladium structures have been found for the complexes Pd 3 [η 3 -1,3-di(pyvaloyl)allyl] 2 (μ,η 2 -acetate) 4 [14b] , Pd 3 [1-3η 3 -6-(α-chloroethyl)cyclooctenyl] 2 Cl 4 [14c] and [Pd 3 (μ-SCy) 4 Cl 2 (PMe 3 )2] [14h] with four bridging ligands and palladium atoms at non-bonding distances. Bent trime- tallic structures have been proposed for [Pd 3 (μ-PPh 2 ) 2 (μ- Cl) 2 (PPh 3 ) 2 ] [14f] , [NEt 4 ] 2 [Pd 3 (μ-Cl) 4 Cl 2 (C 6 F 5 ) 4 ] [14g] , [Pd 3 (η 3 - 1,2,3-tri(p-methoxyphenyl)allyl) 2 (acac) 2 ] [14d] and [Pd 3 (η 3 -2- methylallyl) 2 (Cl) 4 ] [14e] . In the case of allyl complexes, it is believed that the bent structures may result from crystal packing forces rather than steric interactions. Palladium acetate has been found to be trinuclear with a triangular arrangement of non-bonded palladium [12f] and [Pd 3 (μ-O 2 CMe) 3 (μ-MeSCHR) 3 ] [13a] is a mixed-sphere pal- ladium complex in which the solid state nuclearity and structure of palladium acetate is retained. Complexes that are cationic and triangular trinuclear with two triply bridg- ing ligands include [Pd 3 (μ 3 -SPPh 2 ) 2 (PhN=NC 6 H 4 )- (PPh 3 ) 2 ]ClO 4 [13c] and [Pd 3 (C 6 H 4 CH 2 NMe 2 ) 3 (pyS) 2 ]- BF 4 [13d] and with three bridging ligands, capped by a lone sulfur atom as [Pd 3 (μ 3 -S)(SC)(μ-Ph 2 PCH 2 PPH 2 ) 3 ]- [SCN] . 3C 2 H 4 Cl 2 [13b] have been studied. Neutral tripallad- ium triangular complexes with two bridging ligands [Pd 3 (μ- SO 2 ) 2 (BuNC) 5 ] . 2(C 6 H 6 ) [12b] and with three bridging ligands