Uranyl Complexes with Aroylbis(N,N-dialkylthioureas)

Abstract

The reaction of isophthaloylbis( N, N-diethylthiourea), HL, with UO(CHCOO)·2HO and NEt as a supporting base gives a tetranuclear, anionic complex of the composition [{UO(L)}(OAc)], in which the uranyl ions are S, O-chelate bonded. Each two of them are additionally linked by an acetato ligand. Similar reactions of various uranyl starting materials (uranyl acetate, uranyl nitrate, (NBu)[UOCl]) with corresponding pyridine-centered ligands (pyridine-2,6-dicarbonylbis( N, N-dialkylthioureas), HL) yield mononuclear, neutral compounds, in which the thiourea derivatives are coordinated as S, N, N, N, S-five-dentate chelators. The equatorial coordination spheres of the formed hexagonal bipyramidal complexes [UO(L)(solv)] are completed by solvent ligands (HO, MeOH, or DMF). Attempted reactions without a supporting base result in decomposition of the organic ligands and the formation of hexanuclear uranyl complexes with pyridine-2,6-dicarboxylato ligands, while the use of an excess of base results in condensation and the formation of dinuclear [{UO(L)(μ-OMe)}] complexes. A stable complex of the composition [UO(L)] results from reactions of common uranyl starting materials with 2,2'-bipyridine-6,6'-dicarbonylbis( N, N-diethylthiourea) (HL). The equatorial coordination sphere of the neutral, hexagonal bipyramidal complex is occupied by an SNS donor atom set, which is provided by the hexadentate organic ligand. While the uranium complexes with {L} and {L} are labile and rapidly decompose in acidic solutions, [UO(L)] is stable over a wide pH range, and the ligand readily extracts uranyl ions from aqueous solutions into organic solvents.

Uranium Going the Soft Way: Low-Valent Uranium(III) Coordinated to an Arene-Anchored Tris-Thiophenolate Ligand

“…While uranium complexes with hard-donor ligands such as alkoxides, aryloxides, and amides have experienced a development boom in the past few decades, , with numerous examples of small molecule activations − and few catalytic applications, − the coordination chemistry of uranium with the softer chalcogenide sulfur trailed behind with only a fraction of publications, relatively. , Examples of low-valent U­(III) thiolate complexes are still exceedingly rare, − and even more than half of the reported U­(IV)–U­(VI) compounds with thiophenolate ligands are the result of reactivity studies with relatively simple thiophenols, their salts, or their diphenyl disulfide precursors. ,− Sulfur-based ligand design efforts still focus mainly on aspects of lanthanide–actinide separation in nuclear fuel reprocessing, − by exploiting the different degrees of covalency for 4f and 5f metal–ligand bonds. − …”

Synergy Effects in Heavy Metal Ion Chelation with Aryl- and Aroyl-Substituted Thiourea Derivatives

“…Among the most toxic environmental pollutants are heavy metals. − In addition to their toxicity, their persistence in the environment, since they are non-biodegradable; their tendency to biomagnificate; and their bioaccumulative nature make them contaminants whose detection and removal are essential. − Several kinds of heavy metal-detection sensors have been developed, such as biosensors, − electrochemical sensors, − nanomaterial-based sensors, − and optical sensors. − Today, intense research activity is focused on increasing both the sensitivity and selectivity in detection by these devices. − In this way, thiourea derivatives have been developed as a new type of organic ionophores for heavy metal ion selective electrodes. , One of the processes to eradicate such pollutants is chemical remediation, which consists of the complexation of the ions using chelating ligands. − Thiourea derivatives are promising chelating agents of metal cations that have also been proposed for heavy metal ion removal. − Both for sensing and for removal reasons, understanding heavy metal–ionophore activity by organic compounds is thus of high relevance. − In this context, several studies have focused on metal complexes with thiourea derivatives. Coordination chemistry of alkyl and acyl­(aroyl) thioureas of Pt­(II), Pd­(II), and Rh­(III) was reviewed by Koch; the chemistry and metal complexes of acyl-thiourea compounds were recently reviewed in ref ; and uranyl complexes have also been reported with thiourea derivatives …”

“…Coordination chemistry of alkyl and acyl(aroyl) thioureas of Pt(II), Pd(II), and Rh(III) was reviewed by Koch; 55 the chemistry and metal complexes of acyl-thiourea compounds were recently reviewed in ref 56 ; and uranyl complexes have also been reported with thiourea derivatives. 57 Quantum chemistry emerges as a reliable tool to predict ionophore properties of organic compounds. Indeed, the investigation of interactions between metallic cations and organic compounds has attracted huge interest in the last few decades, where an important activity has been developed by means of computational chemistry.…”

Thiosemicarbazone Complexes of Uranium(IV)

“…However, the ligand environment is much more rigid due to the connection to a benzothiazole ring in I-III and a mercaptopyridine in IV and V. The bond distances and angles are of similar values for I-V as in our complexes (UÀ S: 2.71-2.87 Å, UÀ N: 2.45-2.58 Å, SÀ UÀ N: 57-61°). There are also uranyl (VI) complexes with this four-membered coordination motif, [28][29][30] however, due to their different oxidation state these are not directly comparable.…”

“…The bond distances and angles are of similar values for I – V as in our complexes (U−S: 2.71–2.87 Å, U−N: 2.45–2.58 Å, S−U−N: 57–61°). There are also uranyl(VI) complexes with this four‐membered coordination motif, [28–30] however, due to their different oxidation state these are not directly comparable.…”