Anion–ligand interaction in binuclear cyclic dimer complex of a tribenzo-S 2 O 2 macrocycle with silver(I) picrate Joobeom Seo, Mi Ryoung Song, Kaniz Fatima Sultana, Hyun Jee Kim, Jineun Kim, Shim Sung Lee * Department of Chemistry (BK21) and Research Institute of Natural Science, Gyeongsang National University, Chinju 660-701, Republic of Korea Received 6 April 2006; received in revised form 9 May 2006; accepted 13 May 2006 Available online 30 June 2006 Abstract From the reaction of tribenzo-S 2 O 2 macrocyclic ligand (L 1 ) and silver picrate (AgPic), a unique binuclear complex [Ag 2 (L 1 ) 2 (Pic) 2 ](1) has been obtained. The species 1 has been characterised by single-crystal X-ray diffraction analysis providing a definitive proof of its cyclic dimer structure as well as the anion–ligand p–p stacking interactions between L 1 and Pic  . The result of a comparative NMR experiment suggests that the solid structure of 1 is also retained in solution. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Tribenzo-S 2 O 2 macrocycle; Binuclear complex; Silver picrate; Anion–ligand interaction; NMR; p–p stacking 1. Introduction In supramolecular coordination chemistry, the addition- al interactions such as H-bonding, p–p stacking interac- tion, p-coordination, cooperative metal binding, or anion assembly play a significant role not only in the stabilisation of the resulting complexes but also in the transport proper- ties of the related complexes such as solvent extraction and membrane transport [1]. Since such interactions are rela- tively weak but selective, an increasing interest has been in the design of new ionophore system with the suitable synergic effect in the area of separation and detection of the target species [2–4]. The p–p stacking interactions between aromatic units have been relatively well document- ed that aryl groups prefer to associate in either an offset- face-to-face or edge-to-face of an orientation [5]. Our particular interest has been the construction of supramolecular complexes based on sulfur-containing mixed donor macrocycles [6–9] and their use in analytical applications including recognition [10,11] and separation [12] of soft metal ions. Recently, we have realised that the ligand–anion interaction through the aromatic units may contribute significantly to enhance the soft metal ion extractability [12] as discussed elsewhere for hard metal ion system [13]. This work has been stimulated by our extraction results which showed efficient selectivity for sil- ver(I) by thiaoxa-macrocycles through anion–ligand inter- action [12]. Taking this reason into account, the complex system of rigidity enforced tribenzo-S 2 O 2 macrocyclic ligand L 1 with the silver(I) picrate was selected for this pur- pose. Herein we report the synthesis and structural charac- teristics of silver(I) picrate complex of L 1 both in solid and solution states with emphasis on the anion–ligand interaction. 0022-2860/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2006.05.032 * Corresponding author. Tel.: +82 55 751 6021; fax: +82 55 753 7614. E-mail address: sslee@gsnu.ac.kr (S.S. Lee). www.elsevier.com/locate/molstruc Journal of Molecular Structure 827 (2007) 201–205