Synthesis and characterization of a tetrathiafulvalene-salphen actinide complex

Abstract

A new tetrathiafulvalene-salphen uranyl complex has been prepared. The system was designed to study the electronic coupling between actinides and a redox active ligand framework. Theoretical and experimental methods -including DFT calculations, single crystal X-ray analysis, cyclic voltammetry, NMR and IR spectroscopies -were used to characterize this new uranyl complex.A large number of complexes based on organic donor tetrathiafulvalene (TTF) ligands and 3d transition metal centers are known. 1 Complementing studies of these systems are recent efforts to develop TTF-containing complexes of the lanthanide cations. 2 To the best of our knowledge this work has not been extended to the actinide series.Early actinides are typically characterized by more radially extended and accessible f orbitals compared to the lanthanides. Accordingly, substitution of a lanthanide ion for an actinide in a redox active ligand framework offers an opportunity to enhance electronic communication between the ligand and the coordinated metal. 3 Here, we report a uranyl complex (1) based on a TTF-functionalized N,N′-phenylenebis(salicylideneimine) analogue (i.e., TTF salphenH 2 ). Although complex 1 contains a diamagnetic ion, characterizing the interactions between UO 2 2+ and the TTF-ligand represents a crucial first step towards subsequent experiments involving paramagnetic actinyls. Complex 1 was analyzed using a combination of theoretical, electrochemical, and spectroscopic methods. Taken in concert, these studies support the notion that communication between an actinyl cation and a redox active ligand can be achieved. They thus set the stage for more technically challenging studies involving related species such as the PuO 2 2+ cation.The present strategy for obtaining actinide complexes based on TTF-functionalized ligands involves coordinating a uranyl cation to an N,N′-phenylenebis(salicylideneimine) salphentype ligand, specifically the known TTF-salphen dianion ( TTF salphen 2− ). 4 The TTF part of the TTF salphen 2− dianion is redox active and capable of two reversible one-electron oxidations, while the salphen portion of the ligand provides a tetradentate binding site extensively used in actinide science for stabilizing multiple uranium oxidation states (U 4+ , UO 2 1+ , UO 2 2+ ). 3f,5 Complex 1 was thus deemed attractive as a platform for examining electronic coupling effects involving actinide elements and redox active ligands. The synthesis of complex 1 is shown in Scheme 1. Briefly, reacting bis( propylthio)-TTF-benzo-o-diamine 6 with salicylaldehyde and UO 2 (NO 3 ) 2 ·6H 2 O in ethanol provided complex 1 as a red solid in 73% yield. ‡ The 1 H NMR spectrum of this new product was consistent with the uranyl center being complexed by the TTF salphen 2− ligand (see ESI †). 4 Complex 1 (as its methanol complex) was unambiguously characterized in the solid-state via an X-ray crystallographic analysis. Suitable crystals for the analysis were obtained by slow evaporation of a solution of complex 1 in a 1 : 1 mixture of CH 2 C...

Tetrathiafulvalene-annulated [28]hexaphyrin(1.1.1.1.1.1): a multi-electron donor system subject to conformational control

“…1 This has made TTF and its derivatives attractive for use in a wide range of applications, including molecular-based electronics and optoelectronics. 2 As a result, TTF has been incorporated into a variety of molecular scaffolds and ensembles, which have been exploited inter alia as receptors for electron deficient guests, 3 redox active ligands 4 and molecular machines. 5 Moreover, Misaki and coworkers 6 suggested that grafting TTF subunits onto a p-conjugated platform could provide an approach to developing high charge storage capacitors and molecular batteries.…”

Uranyl‐Bound Tetra‐Dentate Non‐Innocent Ligands: Prediction of Structure and Redox Behaviour Using Density Functional Theory

“…[18] of this article for further details). Likewise, oxidation of a series of uranyl‐salophen complexes have recently been determined to form ligand radical compounds, and a tetrathiafulvalene‐salphen uranyl complex has been confirmed by theory and experiment to produce radical species during oxidation of the complex . Although in certain cases oxidation of uranyl(VI) compounds has resulted in oxidation of the coordinating ligand and produced radical species, these may not always undergo or induce further chemical transformations.…”

“…Likewise, oxidation of a series of uranyl-salophen complexes have recently been determined to form ligand radical compounds, [27] and a tetrathiafulvalenesalphen uranyl complex has been confirmed by theory and experiment to produce radical species during oxidation of the complex. [28] Although in certain cases oxidation of uranyl(VI) compounds has resulted in oxidation of the coordinating ligand and produced radical species, these may not always undergo or induce further chemical transformations. However, electrochemical oxidation of the uranyl penta-thiocyanate ([UO 2 (NCS) 5 ] 3À ) complex results in oxidation of thiocyanate ligands and triggers a subsequently unprecedented uranyl(VI) reduction.…”

Exploring the Redox Properties of Bench-Stable Uranyl(VI) Diamido–Dipyrrin Complexes

“… 16 In contrast, the uranyl(VI) α-di-imine diphenolate ( 1 ) ( Figure 1 ) and uranyl(VI) salophens undergo one-electron reduction of the ligand, leading to ligand-centered radical anions and not the expected uranyl(V) complexes. 9 , 10 , 17 …”