Emission spectroscopy has been used for the first time in a spectroscopic study of a family of uranium(IV) halide complexes in non-aqueous media. The room temperature electronic absorption spectra of the simple coordination compounds [Li(THF) 4 ][UX 5 (THF)] (X = Cl, Br, I), [Et 4 N] 2 [UCl 6 ] and UCl 4 in THF have been recorded and all transitions assigned with the aid of a comprehensive computational study using CASSCF and CASPT2 techniques. Excitation into a band of f-d and LMCT character followed by energy transfer into the 5f-orbital manifold accounts for the UV-visible radiative transitions observed in the emission spectra, which have been fully assigned as arising from transitions from the 5f 1 6d 1 electronic configuration to envelopes of states arising from the ground state 5f 2 configuration. The bonding in [Li(THF) 4 ][UCl 5 (THF)] has been further elucidated utilising NBO and AIM calculations which describe the nature of the U-Cl bond as predominantly ionic with some dative covalent character and substantial overlap between the Cl 3p orbitals and 5f and 6d orbitals on uranium. These studies indicate that the emission spectral fingerprint of simple U(IV) compounds of O h , C 4v and C 2v symmetry are similar and characteristic and may be used as a diagnostic tool to assign U(IV) species in solution and by inference, in the environment, in the presence of [UO 2 ] 2+ .

A comprehensive study of the complexes A4[U(NCS)8] (A = Cs, Et4N, (n)Bu4N) and A3[UO2(NCS)5] (A = Cs, Et4N) is described, with the crystal structures of [(n)Bu4N]4[U(NCS)8]·2MeCN and Cs3[UO2(NCS)5]·O0.5 reported. The magnetic properties of square antiprismatic Cs4[U(NCS)8] and cubic [Et4N]4[U(NCS)8] have been probed by SQUID magnetometry. The geometry has an important impact on the low-temperature magnetic moments: at 2 K, μeff = 1.21 μB and 0.53 μB, respectively. Electronic absorption and photoluminescence spectra of the uranium(IV) compounds have been measured. The redox chemistry of [Et4N]4[U(NCS)8] has been explored using IR and UV-vis spectroelectrochemical methods. Reversible 1-electron oxidation of one of the coordinated thiocyanate ligands occurs at +0.22 V vs Fc/Fc(+), followed by an irreversible oxidation to form dithiocyanogen (NCS)2 which upon back reduction regenerates thiocyanate anions coordinating to UO2(2+). NBO calculations agree with the experimental spectra, suggesting that the initial electron loss of [U(NCS)8](4-) is delocalized over all NCS(-) ligands. Reduction of the uranyl(VI) complex [Et4N]3[UO2(NCS)5] to uranyl(V) is accompanied by immediate disproportionation and has only been studied by DFT methods. The bonding in [An(NCS)8](4-) (An = Th, U) and [UO2(NCS)5](3-) has been explored by a combination of DFT and QTAIM analysis, and the U-N bonds are predominantly ionic, with the uranyl(V) species more ionic that the uranyl(VI) ion. Additionally, the U(IV)-NCS ion is more ionic than what was found for U(IV)-Cl complexes.

aWe report that U 3 O 8 , UO 2 (NO 3 ) 2 Á6H 2 O, and UO 2 Cl 2 react with hexachloropropene (HCP) to give UCl 4 in 60, 100, and 92% yields, respectively, and report a protocol to recycle the HCP. This renders the preparation of UCl 4 more accessible and sustainable. 2,5-Dichlorohexachlorofulvene has been identified as a significant by-product from these reactions.In recent years there has been a resurgence of non-aqueous uranium chemistry.1 Such advances rely on the straightforward availability of robust halide starting materials, which are the reagents of choice for introducing new ligand-sets to uranium. For non-aqueous uranium chemistry, straightforward routes to halide starting materials are important because these reagents are not commonly commerically available and must be produced 'in-house'. Apart from uranium(III) triiodide 2 and uranyl(VI) dichloride, 3 perhaps the most commonly used uranium halide starting material is uranium(IV) tetrachloride (UCl 4 ), or solvated derivatives. 4 The latter of these three key starting materials is nowadays prepared by the action of hexachloropropene (HCP) on uranium(VI) trioxide (UO 3 ), since the reaction of carbon tetrachloride on uranium oxides is inconvenient and challenging to undertake on a regular basis. This produces emerald green, solvent-free UCl 4 in high yield. The uranium oxide U 3 O 8 has sometimes been mentioned in the literature as being a suitable starting material for the reaction with HCP. 5 One of us routinely makes UCl 4 by this route in yields of typically 60%. The UCl 4 produced by the UO 3 /HCP route is easily isolated by filtration/washing and is an attractive reagent because the chlorides tend to stabilise the tetravalent state of uranium during reactions, thus suppressing undesirable redox side-reactions. However, the production of UCl 4 from HCP is not without its problems. The reaction initiates via a vigorous radical reaction that produces an exotherm in an already very hot (ca. 200 1C) HCP solution that requires a very long path length condenser to contain, along with brief removal from heat, which in itself requires extra manipulation that may precipitate an accident. In response to this, various variations have been devised, including the portion-wise addition of UO 3 to hot HCP. 4d In principle this circumvents the violent exotherm via a series of much smaller reaction events and can be very effective. However, we note the efficacy of the latter depends on the quality of the UO 3 , and we have found on occasion that particularly wet samples of UO 3 have an induction period. This can risk the build up of unreacted UO 3 , which then suddenly reacts producing an exotherm that might immediately escape out of the flask side arm from which the UO 3 is being introduced. Thus, a safer method can occasionally be turned into a more dangerous one in an unpredictable manner. Increasingly, the use of the UO 3 /HCP reaction is also becoming problematic simply because of the difficulties of obtaining UO 3 , and HCP is becoming increasingly expens...

The reactions of secondary phosphanes with radical sources have been investigated. A stoichiometric dehydrocoupling of Ph 2 PH with 1,1'-azobis[cyclohexane-1-carbonitrile] (VAZO 88) affords tetraphenyldiphosphane in good yields, whilst reduction of the nitrosyl function was observed upon using 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO). Dialkylphosphane -borane adducts also undergo a dehydrocoupling reaction in the presence of VAZO 88 to form R 4 P 2 .Introduction. -The syntheses of molecules featuring PÀP bonds are effectively accomplished via stoichiometric and catalytic processes [1]. Of the former, the two main synthetic methodologies are either via a Würtz type reduction of the phosphane halides or via a dehydrohalogenation of R 2 PX and R 2 PH. The stoichiometric reduction using alkali metals is commonly used, although PÀC bond cleavage of aryl phosphanes has been observed [2]. The catalytic dehydrocoupling reaction to form R 2 PÀPR 2 , RHPÀPHR, or cyclo-(PR) n (n ¼ 5, 6) is gaining in prominence using a Ti-

The synthesis of a series of uranyl compounds via oxidation of [Li(THF) ] (X = Cl, Br, I) have been measured and no significant changes in the position of the emission (515-530 nm) or the lifetimes (ca. 1 μs) are observed in this series. However a bathochromic shift is observed in the U-X LMCT band in the electronic absorption spectrum.