www.elsevier.nl/locate/ica Inorganica Chimica Acta 295 (1999) 171 – 179 Nickel(II) and palladium(II) complexes with acylhydrazone ligands of -diketones: the electronic and steric factors affecting the formation of the dimeric palladium(II) complexes Alessia Bacchi, Mauro Carcelli *, Paolo Pelagatti, Corrado Pelizzi, Giancarlo Pelizzi, Claudia Salati, Paolo Sgarabotto Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica, Uniersita ` di Parma, Parco Area delle Scienze 17 /A, 43100 Parma, Italy Received 12 May 1999; accepted 2 July 1999 Abstract Palladium(II) acetate reacts with butane-2,3-dione bis(octanoylhydrazone) (H 2 oct) giving a dimeric [Pd 2 (oct) 2 ] complex as main product; as shown by X-ray crystal analysis, the ligands are bideprotonated and in each of them one carbonyl oxygen and the two imine nitrogens are bonded to one palladium ion, whereas one hydrazide nitrogen is bonded to the second palladium, giving rise to a N 3 O square planar coordination. The core of the complex is constituted by an unusual six-membered PdN 2 PdN 2 ring. The same arrangement is also found in [Pd 2 (ben) 2 ] (H 2 ben, butane-2,3-dione bis(benzoylhydrazone)) where the alkyl chains of the ligand H 2 oct are substituted by phenyl rings. On the contrary, the corresponding nickel(II) complexes are monomers and the coordination is N 2 O 2 square planar. Monomers are also the nickel(II) and palladium(II) complexes with butane-2,3-dione bis(thiobenzoylhydrazone) and phthalic dicarboxaldehyde bis(benzoylhydrazone). © 1999 Elsevier Science S.A. All rights reserved. Keywords: Hydrazone; Nickel complexes; Palladium complexes; Dimer complexes 1. Introduction The 1,4-disubstituted 1,4-diaza-1,3-butadiene (-di- imine) ligands (Scheme 1(a)) have been studied for their versatile coordination behaviour and the interesting properties of their metal complexes [1]. For example, they can be used as metallomesogens [2] or as homoge- neous catalysts in the copolymerization of styrene and 4-methylstyrene with carbon monoxide [3], or in the hydrogenation of alkene or carbon – carbon cross-cou- pling reactions [4]. These ligands are generally prepared by condensation of a -diketone with an amine, but N -mono- [5] and N,N -di-substituted [6] hydrazines (Scheme 1(b)) were also used. Less is known about the coordination abilities of the ligands obtained from con- densation of -diketones and hydrazides [7] (Scheme 1(c)) even if some studies on their analytical use are reported [8]. As an extension of our work on the chelating proper- ties of polydentate ligands derived from 1,2-diketones Scheme 1. * Corresponding author. Fax: +39-0521-905 557. E-mail address: carcelli@ipruniv.cce.unipr.it (M. Carcelli) 0020-1693/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved. PII:S0020-1693(99)00349-7