Self-assembly of organometallic Pd(II) complexes via CH 3 ÁÁÁp interactions: The first example of a cyclopalladated compound with herringbone stacking pattern E.T. de Almeida a , A.E. Mauro b, * , A.M. Santana b , S.R. Ananias b,c , A.V.G. Netto b , J.G. Ferreira c , R.H.A. Santos c a Departamento de Cie ˆncias Exatas, UNIFAL, 31130-000 Alfenas, MG, Brazil b Instituto de Quı ´mica de Araraquara, UNESP, CP 355, 14801-970 Araraquara, SP, Brazil c Instituto de Quı ´mica de Sa ˜o Carlos, USP, CP 780, 13560-970 Sa ˜o Carlos, SP, Brazil Received 13 June 2007; accepted 28 August 2007 Abstract Two binuclear cyclometallated compounds [Pd(C 2 ,N-dmba)(l-N 3 )] 2 (1) and [Pd 2 (C 2 ,N-dmba) 2 (l-N 3 )(l-Cl)] (2) (dmba = N,N-dim- ethylbenzylamine) have been synthesized and characterized by elemental analysis, IR and NMR spectroscopies and single crystal X-ray diffraction crystallography. The ability of CH 3 groups to form C(sp 3 )AHÁÁÁp hydrogen bonds with phenyl rings is responsible for the molecular self-assembly within the crystals of 1 and 2. Compound 1 crystallizes as one-dimensional supramolecular chains whereas the crystal packing of 2 consists of a herringbone of sandwiches composed by two inversely related [Pd 2 (C 2 ,N-dmba) 2 (l-N 3 )- (l-Cl)] molecules. Ó 2007 Elsevier B.V. All rights reserved. Keywords: Supramolecular chemistry; C(sp 3 )AHÁÁÁp interactions; Cyclopalladated compounds; Self-assembly The design of metal supported supramolecular architec- tures aimed at creating novel materials with useful chemical and/or physical properties represent one of the most active research topics of current chemistry and molecular material science [1,2]. Since the properties depend essentially on the crystal structure, the building blocks must possess the required molecular structure as well the appropriate molec- ular orientation and assembly in the solid state [2]. One of the most successful strategies used in the construction of supramolecular structures takes advantage of the strength and directing capability of hydrogen bonding as critical organizing elements [3]. Although conventional strong hydrogen bonds (e.g. OAHÁÁÁO and OAHÁÁÁN) have been considered to be of importance in crystal engineering, they are not the only class of intermolecular interaction useful for directing molecular self-assembly. There is an increas- ing interest in the role played by weak intermolecular forces such as pÁÁÁp stacking, XAHÁÁÁA (X = C, N, O; A = O, Cl, p), halogenÁÁÁhalogen, in determining molecu- lar packing and crystal structure stability [4]. In particular, the CAHÁÁÁp interactions are the weakest among non-con- ventional hydrogen bonds and are considered as the inter- action between soft acids and soft bases [3,5]. The CAHÁÁÁp interactions are very interesting because of the wide range of CAH group acidity and p-basicity as well the frequent occurrence of CAH groups in almost all organic molecules [3]. Therefore, the cooperative action of such weak interactions in molecular recognition and self-assembly process should not be underestimated. Despite the fact that such interactions have been exten- sively explored and reviewed in organic and biological chemistry, there are a growing interest on CAHÁÁÁp hydro- gen bonds in the crystal packing of organometallic and 1387-7003/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2007.08.020 * Corresponding author. Tel.: +55 01633016625; fax: +55 01633227932. E-mail address: mauro@iq.unesp.br (A.E. Mauro). www.elsevier.com/locate/inoche Inorganic Chemistry Communications 10 (2007) 1394–1398 ARTICLE IN PRESS