A homoleptic uranium thiolate: synthesis, structure, and fluxional behavior of [Li(dme)]4[U(SCH2CH2S)4] and reaction with carbon disulfide

Abstract

We have synthesized and fully characterized a tetrakis(ethane-1,2-dithiolato)uranate(IV), (Li(dme)){sub 4}(U(edt){sub 4}) (1), the first homoleptic dithiolate complex of an f element. The complex crystallizes with an additional DME solvent molecule, and its structure was determined by an x-ray study. The coordination geometry about the uranium center is dodecahedral, and four lithium cations surround the (U(edt){sub 4}){sup 4{minus}} anion. Each lithium bridges two sulfur atoms and is further coordinated by a dme molecule. We have analyzed the nature of the U-S bonds, using the extended Hueckel method, to find that U 6d, 7s, and 7p orbitals are responsible for interactions with sulfur orbitals, thus, no significant U 5f participation in bonding is discernible, and that U-S {pi} interactions are weak. The low temperature {sup 1}H NMR spectra in the THF-d{sub 8} exhibit four resonances associated with the edt protons. The relative size of their paramagnetic isotropic shifts can be interpreted on the basis of the pseudocontact (dipolar) term, the analysis of which suggests the solid-state dodecahedral structure to be retained in solution. The thermodynamic properties and crystal structure of the complex was determined, and they are reported herein. 53 refs., 5 figs., 8 tabs.