Dioxouranium(VI) complexes with 2,6-acetylpyridinebenzoylhydrazones and -semicarbazones C.C. Gatto a , E. Schulz Lang a , A. Jagst b , U. Abram b, * a Departamento de Quimica, Universidade Federal de Santa Maria, 97.111 Santa Maria-RS, Brazil b Freie Universita ¨ t Berlin, Institute of Chemistry, Fabeckstr. 34-36, D-14195 Berlin, Germany Received 13 February 2004; accepted 10 July 2004 Available online 26 August 2004 Abstract Benzoylhydrazones and semicarbazones derived from 2,6-diacetylpyridine react with common dioxouranium(VI) compounds such as uranyl nitrate or [NBu 4 ] 2 [UO 2 Cl 4 ] to form air-stable complexes. 2,6-Diacetylpyridinebis(benzoylhydrazone) (H 2 L 1 ), 2, 6-diacetylpyridinebis(N4-phenylsemicarbazone) (H 2 L 2 ) and the asymmetric proligand 2,6-diacetylpyridine(benzoylhydrazone)- (N4-phenylsemicarbazone) (H 2 L 3 ) give yellow products of the composition [UO 2 (L)]. The neutral compounds contain doubly deprotonated ligands and possess uranium atoms with distorted pentagonal-bipyramidal coordination spheres. The equatorial coordination spheres of the metal atoms can be extended by the addition of a monodentate ligand such as pyridine or DMSO. The uranium atoms in the resulting complexes have hexagonal-bipyramidal coordination environments with the oxo ligands in axial positions. X-ray diffraction studies on [UO 2 (L 1 )(DMSO)], [UO 2 (L 2 )], [UO 2 (L 2 )(DMSO)] and [UO 2 (L 3 )] show relatively short U–O bonds to the benzoylic oxygen atoms between 2.273(6) and 2.368(5) A ˚ . This suggests a preference of these donor sites of the ligands over their imino and amine functionalities (U–N bond lengths: 2.502(7)–2.671(7) A ˚ ). The addition of a sixth ligand to the equatorial coor- dination sphere results in a lengthening of the metal–pyridine bonds. Ó 2004 Elsevier B.V. All rights reserved. Keywords: Uranium; Benzoylhydrazones; Semicarbazones; Actinides; Structure analysis 1. Introduction As a part of our systematic studies of the coordina- tion chemistry of the early actinide elements, we re- cently published a report on the structural chemistry of thiosemicarbazonato complexes of uranium(VI) [1]. The formation of complexes with moderate stabil- ity was observed with acetylpyridine thiosemicarba- zone. The presence of the pyridine nitrogen atom was mandatory for the formation of chelate com- plexes. This additional donor site is obviously essential to establish a bond between the relatively ÔhardÕ metal ion UO 2 2+ and ÔsoftÕ donor sites such as the thione sulfur atoms in thiosemicarbazones. More stable com- plexes are expected with ÔharderÕ donor atoms such as oxygen, as are provided by semicarbazones or hydra- zones. A number of studies have been undertaken with both ligand systems and the formation of che- lates with various compositions has been suggested on the basis of spectroscopic data [2]. Some of the compounds have been proposed for the spectrophoto- metric determination of metal ions including UO 2 2+ [3], but less is known about the composition of the coordination environment of the metal. First struc- tural reports of complexes with 2,6-diacetylpyridine- bis(2 0 -pyridyl)hydrazones [4], benzoylhydrazones [5] 0020-1693/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2004.07.011 * Corresponding author. Tel.: +49 30 83854002; fax: +49 30 838542676. E-mail address: abram@chemie.fu-berlin.de (U. Abram). www.elsevier.com/locate/ica Inorganica Chimica Acta 357 (2004) 4405–4412