Nature of the dioxobis(tropolanato)uranium(VI) system and its complexes with neutral ligands

Uranyi tropolonato-complexes, of general formula UO2t2 and UO2t2,xH2O (Ht = tropolone) have been prepared. Physical properties are discussed and structures suggested. Their reactivities were tested by preparing adducts with a series of neutral ligands L (L = methanol, water, dimethyl sulphoxide, pyridine N-oxide, triphenylphosphine oxide, cyclohexanone, pyridine, and aniline). The crystal structure of the pyridine (py) adduct UO2t2(py) has been determined by X-ray diffraction methods by the heavy-atom method from counter data on 3252 reflections, and refined to R 0·058 by a full-matrix least-squares procedure. The monoclinic unit cell, space group I2/a(standard cell C2/c), has dimensions a= 17·88(1), b= 12·69(1), c= 16·79(1)Å, β= 98·32(10)° for Z= 8. The molecule has approximately C2v symmetry. Two tropolonato-groups and the pyridine ligand are displaced slightly from the plane perpendicular to the linear uranyl group. The U–O(uranyl) distances are 1·78 and 1·79 Å; the four U–O(eq) distances are almost equal (2·37–2·38 Å) and U–N(py) is 2·61 Å.