Journal of Inclusion Phenomena and Macrocyclic Chemistry 48: 31–35, 2004. © 2004 Kluwer Academic Publishers. Printed in the Netherlands. 31 Inclusion of Two PhP(O)(OH) 2 Guest Molecules into the Cavity of the Macrocyclic Cavitand Cucurbit[8]uril ELENA V. CHUBAROVA ∗ , DENIS G. SAMSONENKO, MAXIM N. SOKOLOV, OLGA A. GERASKO, VLADIMIR P. FEDIN and JAVIER G. PLATAS Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences, Academician Lavrentiev Avenue 3, Novosibirsk 630090, Russia University of La Laguna, 38200, Tenerife, Canary Islands, Spain (Received: 15 July 2003; in final form: 27 July 2003) Key words: crystal structure, cucurbit[8]uril, inclusion compounds, phenylphosphonic acid Abstract A new inclusion compound which is a supramolecular adduct of cucurbit[8]uril with two guest molecules of phenylphos- phonic acid, PhP(O)(OH) 2 , included into the cavity as “two guests in host” is reported. The guests match both size and hydrophilicity/hydrophobicity requirements. Two phenyl groups of molecules of PhP(O)(OH) 2 are directed toward the center of the large hydrophobic cavity whereas the PO(OH) 2 groups are outward-looking and bound with each hydrophilic portal of cucurbit[8]uril by a short hydrogen bond. Introduction Selective inclusion of guest molecules in the host cavity is a very important problem of modern chemistry. Numerous complexes generated by such host macrocyclic organic mo- lecules as crown ethers [1], cryptands [2], calixarenes [3] or cyclodextrins [4] are presently available. The encapsu- lation of inert gases, metal ions or organic molecules into the cavities of these molecules gives rise to stable com- pounds with unusual structures and interesting properties. Cucurbit[n]urils (n = 5–10) [C 6 H 6 N 4 O 2 ] n are also known to include suitable size guests. They can be described as barrel-shaped macrocyclic molecules with an internal cavity and a rigid structure. They have two identical portals on each side of the ‘barrel’ which are fringed by n carbonyl groups. The dimensions of the cavity vary with n. The cavity is hydrophobic, but the portals ∗ Author for correspondence. E-mail: elena@che.nsk.su are hydrophilic. This means that guests must match both size and hydrophilicity/hydrophobicity requirements [5]. Recently obtained cucurbit[8]uril (n = 8) has the largest cavity (V = 479 Å 3 ), d cavity = 8.8 Å, d portal = 6.9 Å. h cavity = 9.1 Å. Thus the cavity size of cucurbit[8]uril al- lows to include rather bulky molecules, for example such macrocycles as 1,4,7,10-tetraazacyclododecane (cyclen) and 1,4,8,10-tetraazacyclotetradecane (cyclam). These inclusion compounds are stabilized primarily through van der Waals interactions between the inner macrocycle (guest) and outer cavitand (host) [6]. Large cavity cucurbit[8]uril can include even two guest molecules, for example, two such bulky molecules as 2,6- bis(4,5-dihydro-1H-imidazol-2-yl)naphthalene can be ac- commodated. Here, not only van der Waals interactions and the hydrophobic effect but also hydrogen bonding between the protonated dihydroimidazole substituents and the portal oxygen atoms of cucurbit[8]uril play an important role in the formation of inclusion compound [7]. Two naphthalene rings within the cavity are located parallel to each other at a distance of about 3.4 Å, which is indicative of π -π interactions between these rings [8]. The encapsulation of two or more guest molecules into the cavity of cucurbit[8]uril is of great interest in the view of the unique possibility of studying new types of stereoi- somerism, bimolecular reactions and the behavior of the molecules in the microenvironment. The ability of cucur- bit[8]uril to accommodate two closely spaced guests located in a forced orientation allows one to use it as the syn- thetic molecular container in which bimolecular reactions between specially selected guests can proceed with high regio- and stereoselectivity. Thus, photodimerisation of 4,4 ′ -