CRYSTAL STRUCTURES OF URANYL/CALIXARENE COMPLEXES. P. Thuery and M. Nierlich, CEA/Saclay, SCM, Bat. 125, 91191 Gif-sur-Yvette, France

The interest of calixarene derivatives as 'uranophiles' is well known from solution experiments. However, few actinide complexes of calixarenes have been structurally described: the list is limited to the uranyl (UO₂²⁺) complex of bis(homo- oxa)-p-tertbutylcalix[4]arene and the thorium complex of p-tert-butylcalix[8]arene reported by Harrowfield et al. [1] and the three uranyl complexes here reported

With p-tert-butylcalix[5]arene, the uranyl ion forms an inclusion complex: the metal ion is surrounded by the five oxygen atoms of the calixarene which is in the cone conformation [2]. A triethylammonium ion is included in the calixarene cavity.

A dimeric species is formed with p-tert-butylcalix[6]arene: two uranyl ions bridge two calixarene moieties, giving rise to an unprecedented assembly type [3]. Uranyl ions are in a nearly regular equatorial square planar environment. An hydronium ion and an acetonitrile molecule are included in each calixarene cavity. Two forms of the binuclear uranyl complex of p- tertbutylcalix[8]arene have been described [4]. The two ions are encompassed by the macrocycle in the pleated loop conformation. Each ion is bonded to four oxygen atoms from the calixarene and to a bridging hydroxyl ion.

1. J.M. Harrowfield, M.I. Ogden and A.H. White: J. Chem. Soc. Dalton Trans., 979 and 2625 (1991).

2. P. Thuéry and M.Nierlich: submitted to J. Incl. Phenom.

3. P. Thuéry, M. Lance and M. Nierlich: Supramol. Chem., in press.

4. P. Thuéry, N. Keller, M. Lance, J.D. Vigner and M. Nierlich: Acta Cryst. C51, 1570 (995); ibid.: New J. Chem. 19, 619 (1995).