Silicon Chemistry 2: 55–71, 2003. C  2004 Kluwer Academic Publishers. Printed in the Netherlands. 55 Crystalline inclusion compounds derived from bulky organosilicon hosts – design, synthesis, structure and stability Silke I. Nitsche 1 , Edwin Weber 1,∗ , Wilhelm Seichter 1 , Nikoletta B´ athori 2 , Kayrat M. Beketov 3 & Gerhard Roewer 4 1 Institut f ¨ ur Organische Chemie, Technische Universit¨ at Bergakademie Freiberg, Leipziger Str. 29, D-09596 Freiberg/Sachsen, Germany; ∗ Author for correspondence (e-mail: edwin.weber@chemie.tu-freiberg.de) 2 Chemical Research Center, Institute of Chemistry, Hungarian Academy of Sciences, P.O. Box 17, 1525 Budapest, Hungary 3 Institute of Chemical Sciences, Ualikhanov Str. 106, Almaty, 480100 Kazakstan 4 Institut f ¨ ur Anorganische Chemie, Technische Universit¨ at Bergakademie Freiberg, Leipziger Str. 29, D-09596 Freiberg/Sachsen, Germany (Received 14 July 2003; accepted 10 February 2004) Key words: crystalline inclusion compounds, inclusion hosts, organic guests, organosilicon compounds, thermal analysis, X-ray structure Abstract New organosilicon compounds 1–3 featuring bulky triphenylsilyl moieties attached to rigid linear or trigonal spacer units have been synthesized and demonstrated to act as clathrate hosts, yielding crystalline inclusion compounds mostly with apolar and aprotic dipolar guest molecules, while the nonbulky dimethylphenylsilyl or trimethylsilyl substituted analogous compounds 4 and 5, which were also synthesized, proved inefficient. X-ray crystal structures of the inclusion compounds 1·DMF (1:1), 1·pyridine (1:1), 2·1,4-dioxane (2:1), 2·pyridine (2:1), 2· p-xylene (2:1), 2·H 2 O (2:1) as well as of the unsolvated compounds 2 and 5 are described, and thermal stability studies of selected clathrates are reported. Introduction Owing to their great promise in a variety of fundamen- tal and practical uses [1, 2], crystalline inclusion com- pounds (clathrates) and similar co-crystalline systems have raised considerable interest in the last few years [3]. This has stimulated the development of new strate- gies for crystalline inclusion formation and motivated the design of novel host types [4–6]. In many cases of these host compounds, a rigid and bulky substituted framework structure incorporating acetylene or arene moieties is involved [7, 8]. Hence, host molecules for crystalline inclusion formation are mostly organic [3, 7] while others containing inorganic elements, such as silicon atoms [9], are very rare [10]. On the other hand, it has been shown that triphenylsilanol [11] is a remark- ably selective inclusion host for ethanol [12], unlike the pure organic counterpart triphenylmethanol [13] which is selective for methanol [14]. With this in mind, the design of new silicon-containing host compounds was a challenge to us. This work reports on the synthesis of three spe- cific organosilicon host compounds 1–3 (Scheme 1), including also compounds 4 and 5 for the purpose of comparison. Their crystal inclusion (clathrate for- mation) properties are discussed and crystal structures of five selected inclusion compounds including differ- ent hosts (1, 2) and organic guests of different com- pound classes as well as the structures of a hydrated (2) and of two unsolvated compound species (2, 5) are presented. Host design and synthesis Following the strategies of ‘dumb-bell shape’ and ‘awkward constitution’ that have proved very useful in the design of pure organic host molecules [15], the