Interesting structures and properties as well as perspectives of practical use motivated intensive studies of various calixarene complexes in recent years. The development of new catalysts increases also the interest in the design and synthesis of supramolecular metallocalixarene arrays. The novel cerium calixarene complexes [p-tBu-calix[4](OMe)₂(O)₂Ce(acac)₂] (1) and [p-tBu-calix[4](OMe)₂(O)₂Ce(hfac)₂] (2) were recently synthesized in an equimolar reaction between p-tBu-calix[4](OMe)₂(OH)₂ and cerium complexes Ce(acac)₄ (acac = acetylacetonate), and Ce(hfac)₄ (hfac = 1,1,1,5,5,5-hexafluoro-acetylacetonate), respectively [1].

The cerium oxidation state in such complexes is discussed intensively, whereas contradictory results are reported [2]. In the present study, X-ray photoelectron spectroscopy (XPS) with monochromatic Al Kα excitation (1486.74 eV) was applied in a "fast transfer" mode [3]. The experiments revealed an irradiation-induced decrease of the Ceox values of both complexes dependent upon X-ray exposure. The detailed study of the dynamical response of the Ce_ox to X-ray irradiation allowed the determination of Ce_ox at "zero irradiation" [3.60 for complex (1) and 3.65 for complex (2), respectively]. Neither vacuum-induced reduction, nor re-oxidation of the irradiated compounds in air were observed suggesting the possibility of the long-lasting X-ray induced tuning of Ce_ox in a range of at least 3.65 to 3.26.

[1] J. Gottfriedsen, D. Dorokhin, Z. allg. anorg. Chem. 631 (2005) 2928;

[2] C. H. Booth, M. D. Walter, M. Daniel, W. W. Lukens, R. A. Andersen, Phys. Rev. Lett. 95 (2005) 267202, and references therein

[3] Y. Suchorski, L. Rihko-Struckmann, F. Klose, Y. Ye, M. Alandjiyska, K. Sundmacher, H. Weiss, Appl. Surf. Sci. 249 (2005) 231.

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