The role of preorganization of hydrazone moieties on tetrathiacalix[4]arene platform for their conformational and binding properties from the view of structural investigation Sergey N. Podyachev a,⇑ , Bulat M. Gabidullin a , Victor V. Syakaev a , Svetlana N. Sudakova a , Aidar T. Gubaidullin a , Wolf D. Habicher b , Alexander I. Konovalov a a AE Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Center of Russian Academy of Sciences, Arbuzov Str., 8, 420088, Kazan, Russia b Dresden University of Technology, Institute of Organic Chemistry, Bergstraße 66, 01069 Dresden, Germany article info Article history: Received 22 March 2011 Received in revised form 23 June 2011 Accepted 23 June 2011 Available online 2 July 2011 Keywords: Tetrathiacalix[4]arene Hydrazone Crystal structure Conformation Complexation Calix[4]arene abstract The IR, 1 H and 13 C NMR data, as well as conformation and dynamic behaviour of tetrathiacalix[4]arenes functionalized by hydrazone fragments are reported. The influence of isomers of thiacalix[4]arenes, the removal of tert-butyl groups from upper rim of macrocycle and the replacement of a phenyl substituents in the hydrazone fragments by 2-pyridyl ones on conformational properties of the compounds are dis- cussed. The structural peculiarities of the cone isomer of 25,26,27,28-tetrakis[N 2 -(2-pyridinylmethylid- ene)hydrazinocarbonylmethyloxy]-2,8,14,20-tetrathiacalix[4]arene and the 1,3-alternate isomer of 25,26,27,28-tetrakis[N 2 -(benzylidene)hydrazinocarbonylmethyloxy]-2,8,14,20-tetrathiacalix[4]arene in solution are compared with their crystal structures obtained by X-ray analysis. The correlation between extraction efficiency data obtained for these compounds earlier and the conformational features of calix[4]- arene hydrazone derivatives studied in this work was performed. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction An important direction in modern chemistry is the design of li- gands showing receptor properties [1,2]. Receptor molecules pos- sessing high affinity and selectivity towards specific substrates are intensively studied in supramolecular chemistry [3,4]. The pre- organization of binding groups on a macrocycle framework is a commonly used approach in the design of receptor molecules. Calix[n]arenes which can be easily modified by various functional groups are widely applied as a macrocyclic platform for this pur- pose [5–7]. The numerous studies on complex ability of calix[n]are- nes and their various derivatives testify that their complexation properties and selectivity depend not only on the nature of substi- tutes but also on their topology and conformation [7,8]. Incorpora- tion of donor groups on the macrocyclic platform can be resulted in the change of their topology due to the mutual influence of groups, which affects the complexation properties of the receptor. There- fore, to understand the reasons determining these properties, the accurate information about conformational properties and three- dimensional structure of receptor molecules is rather important. Chelate groups with N,O-donor atoms are very popular in the ligand design. Compounds bearing hydrazide and hydrazone groups proved to be especially attractive due to their application as objects of investigation in biology and medicine [9–12] and due to the use them as materials for optoelectronic devices [13]. Moreover, these compounds can be used as highly effective extractants of transition metal ions [14–18] and key reagents for the synthesis of various nitrogen containing derivatives [19]. In re- cent years a number of publications devoted to the synthesis and application of bis-hydrazide and – hydrazone derivatives is notably grown. These compounds in contrast to their monomeric ana- logues can form complicated supramolecular structures and reveal unusual physico-chemical properties [20]. The cis/trans-amide conformational isomerism and E/Z-isomerisation around double C@N bond effect significantly on the complex formation properties of these compounds. The favourable mutual orientation of donor groups and their high ‘‘local concentration’’ in the molecule can also enhance their binding properties. Recently we synthesized novel tetrahydrazone derivatives of calix[4]arenes (1–8) (see Fig. 1) and evaluated their extraction properties towards a wide range of metal ions [21,22]. High selec- tivity and efficiency of d-ions binding by these new tetrahydraz- ones was established. Moreover, the influence of several factors, such as the isomeric form of thiacalix[4]arene, the presence or ab- sence of tert-butyl groups at upper rim on these properties are also revealed. These factors can also affect the cis/trans-amide confor- mational isomerism of hydrazone fragments (Fig. 2) and as a result 0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2011.06.028 ⇑ Corresponding author. Fax: +7 843 2731872. E-mail address: spodyachev@iopc.ru (S.N. Podyachev). Journal of Molecular Structure 1001 (2011) 125–133 Contents lists available at ScienceDirect Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc