Zero-, mono- and diperiodic uranyl ion complexes with the diphenate dianion: influences of transition metal ion coordination and differential UVI chelation

Abstract

Diphenic acid (H₂dip) has been used to synthesize nine homo- or heterometallic uranyl ion complexes under solvo-hydrothermal conditions. The diphenate ligand dip²⁻ adopts different coordination modes, mixtures of κ²-O,O′-chelation by individual carboxylate groups, chelation involving both carboxylate groups, and bridging, resulting in different associations of the cations present. [UO₂(dip)] (1), [UO₂(dip)(bipy)] (2), and [UO₂(dip)(phen)] (3) crystallize as monoperiodic coordination polymers, complex 1 with the bridging and both chelation modes of the ligand, and 2 and 3 with only the bis-κ²-O,O′-chelated mode and further chelation by 2,2′-bipyridine (bipy) or 1,10-phenanthroline (phen). The two isomorphous complexes [H₂NMe₂]₂[(UO₂)₂(dip)₃] (4) and [(UO₂)₂Ag₂(dip)₃(H₂O)(CH₃CN)] (5) display ladder-like monoperiodic arrangements with the hydrogen bonded H₂NMe₂⁺ or carboxylate-bound, decorating Ag⁺ cations occupying similar positions within the chains. [Ni(R,S-Me₆cyclam)(H₂O)₂][UO₂(dip)₂] (6) contains a discrete dianionic mononuclear species, while [(UO₂)₂(dip)₂(Hdip)₂Ni(cyclam)]·2H₂O·2CH₃CN (7) crystallizes as a monoperiodic, heterometallic polymer, with further formation of layers through reciprocal hydrogen bonding of the carboxylic acid groups. A discrete dinuclear dianionic complex is present in [Cu(R,S-Me₆cyclam)][UO₂(dip)(NO₃)]₂ (8), which crystallizes together with [(UO₂)₃(dip)₄Cu(R,S-Me₆cyclam)(H₂O)₂]·6H₂O (9), a diperiodic assembly in which uranyl-containing dimeric units are assembled in chains through diaxial carboxylate coordination of Cu(R,S-Me₆cyclam)²⁺ cations, with further bridging by uranyl cations generating a network with the fes topology. The uranyl emission spectra of complexes 3, 4 and 5 show the usual vibronic fine structure, while uranyl emission in 7 is largely quenched.