Uranium(V) and uranium(IV/V) mixed valence complexes with p-tert-butylhomocalix[n]arenes (n = 4, 6)

The homocalixarenes p-tert-butyltetrahydroxy[3.1.3.1]metacyclophane (H4L1) and p-tert-butylhexahydroxy[2.1.2.1.2.1]metacyclophane (H6L2) react with UCl4 to give new polyphenoxide uranium complexes which have been characterized by X-ray diffraction. In the mononuclear compound [Hpy][UCl2(L1)] · 2.5py (2), the UV centre is bound to the four phenoxide groups and two chlorine atoms. Further inclusion of hydrogen bonded counter-ions and solvent molecules in the macrocycle cavity results in dimerization through weak interactions. The tetranuclear complex [U4Cl2O2(L2)2(H2O)(thf)] · 3thf (3) is a mixed valence compound comprising two UIV and two UV centres bound to three or four phenoxide groups each and bridged by two μ3-oxo, two chlorine and two phenoxide groups. The localization of the UIV and UV ions is indicated by the differing bond lengths. The crystal structure of the uncomplexed macrocycle H6L2 · 5py (1) is also reported.

Graphical abstractUCl4 reacts with homocalixarenes comprising four or six phenolic units to give either a mononuclear UV complex with the smaller macrocycle or, with the larger one, a tetranuclear UIV/UV mixed valence species built from two macrocycles, two μ3-oxo and two bridging chlorine atoms. In both cases, all the phenoxide groups are metal-bound. The mononuclear species assembles to form a dimeric capsule through weak interactions with the counter-ions.Figure optionsDownload full-size imageDownload as PowerPoint slide