Synthesis, structure and magnetic behaviour of dinuclear uranium( iv ) complexes with a ‘calixsalophen’ type macrocycle

Treatment of UCl4 with the octadentate tricompartmental ‘calixsalophen’ type macrocycle H4L1 [N,N:N′,N′-bis(2,2′-dihydroxy-3,3′-dimethylidene-5,5′-di-tert-butylbiphenyl)benzene-1,2-diamine] in THF or pyridine gave the complexes [U2L1Cl4] (1) and [U2L1Cl4(py)2] (2), respectively. The crystal structures of 1·4THF and 2·3py are centrosymmetric, the metal atoms occupying the N2O2 cavities with either a pentagonal bipyramidal environment in 1, two Cl atoms being in apical positions, or a dodecahedral environment in 2. Reaction of U(acac)4 (acac = MeCOCHCOMe) with H4L1 in THF did not afford the corresponding acetylacetonate product but gave instead the isomeric complex [U2L1(acac)4] (3), in which one of the two N2O2 cavities is empty, one of the uranium atoms occupying the central O4 site. The dinuclear complex [U2(HL3)(acac)5] (4) was obtained by treating U(acac)4 with H4L1 in pyridine; in this case, the macrocyclic ligand L1 was transformed into its mono(benzimidazole) derivative L3. The eight-coordinate uranium atoms in 3·5THF and 4·2py adopt a distorted square antiprismatic configuration. The magnetic properties of compounds 1 and 3 were investigated.