Comparative study on the transition metal complexes of a novel thiacalix[4]arene derivative A. Suwattanamala a , D. Appelhans b , M. Wenzel c , K. Gloe c , A.L. Magalha ˜es a, * , J.A.N.F. Gomes a a REQUIMTE, Departamento de Quı ´mica, Faculdade de Cie ˆncias, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal b Leibniz Institute of Polymer Research Dresden, Hohe Strasse 6, 01069 Dresden, Germany c Institute of Inorganic Chemistry, TU Dresden, 01062 Dresden, Germany Received 11 April 2005; accepted 6 July 2005 Available online 15 August 2005 Abstract A comparative study on Zn 2+ and Cu 2+ complexes of the novel compound 5,11,17,23-tetra-tert-butyl-25,27-bis{[4-(methoxycar- bonyl)phenyl]methoxy}-2,8,14,20-tetrathiacalix[4]arene, that possesses potential as a core unit for the construction of molecular receptors, is presented using semiempirical AM1 calculation. The possible structures of each metal complex and their corresponding energetic data are compared with the parent 5,11,17,23-tetra-tert-butyl-2,8,14,20-tetrathiacalix[4]arene. The complexation ability of both thiacalix[4]arenes towards the two metal ions is discussed on the basis of binding energies. Both thiacalix[4]arene 1:1 complexes show higher complexation ability towards Cu 2+ . However, 5,11,17,23-tetra-tert-butyl-25,27-bis{[4-(methoxycarbonyl)phenyl]meth- oxy}-2,8,14,20-tetrathiacalix[4]arene presents lower complexation ability when compared with the 5,11,17,23-tetra-tert-butyl- 2,8,14,20-tetrathiacalix[4]arene. The results of liquid–liquid extraction experiments of the thiacalix[4]arenes are in good agreement with the theoretical calculations. Ó 2005 Elsevier B.V. All rights reserved. Keywords: Thiacalix[4]arenes; Metal complex; Complexation ability; AM1 calculations; Liquid–liquid extraction 1. Introduction The construction and control of three-dimensional molecular structures with complexing properties are re- search topics in dendrimer and supramolecular chemis- try mimicking the function of biomolecules [1,2]. Due to the macrocyclic structure and simple modification of the phenol unit, calixarenes have been used as a scaffold to construct artificial enzymes for chemical transformation and molecular recognition [3]. In the last decade, thiacalixarenes were reported as new com- pounds in the family of calixarenes substituting only the bridging methylene groups between the phenolic units by sulfur atoms [4]. In particular, thiaca- lix[4]arenes have been proposed as precursors for po- tential applications based on (a) the large diversity in host–guest properties [5] due to the increasing number of coordination sites in the lower and upper rims and, (b) the versatile use in the construction of different and stable conformers [6]. Therefore, the thiacalix[4]arene is suited to support the formation of different molecular shapes with complexing thiacalixarene moieties as cen- tral unit for the construction of dendritic-shelled molecular receptors, shown in Scheme 1, to enhance the stability of host–guest interactions, e.g., towards biological environment. Theoretical calculations are used nowadays to describe the metal complexation of core units 1 and 2 [6c] in Scheme 1, to optimize 0301-0104/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.chemphys.2005.07.024 * Corresponding author. Tel.: +351 226 082804; fax: +351 226 082959. E-mail address: almagalh@fc.up.pt (A.L. Magalha ˜es). www.elsevier.com/locate/chemphys Chemical Physics 320 (2006) 193–206