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

Abstract

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.