Abstract
Few U (III) complexes with organic ligands have previously been isolated . The present work reports the preparation of many new U(III) adducts with neutral oxygen-donor ligands having the stoichiometries (X- usually ={BPh4} or {PF6}). 1. {UL4}X3, L= a. R2N. CO. (CH2)n. CO. NR2 and R2N. CO. CH2. CMe2. CH2-CO. NR R=Me, series 1 (n=1-4), R=Et, series 2 (n=1-4) ; b. 1,1'-methylenebis (pyrrolid-2-one) ; c. N, N, N', N', N'', N", N''', N"'-octamethylphosphoramide; d. O,O' ,O'', O'''-tetraethylethylenediphosphonate; e. O,O'-diethyl-N, N-dimethylcarbcnylmethylenephosphonate. 2. . {UL3]X3 L= a. 4,4'-diantipyrylmethane; b. O,O' ,O'' ,O'''-tetraethyltrimethylenediphosphonate (X ={PF6-} only). 3. {UL2{PF6}3 , L=18-crown-6. 4. {UL1. 5}X3, L= a. ethylenediaminetetrakis (N, N-dimethylacetamide), (X-= {PF6} only); b. N, N, N', N' -tetramethylsuccinamide (X-=Cl only). 5. ULCl3. nH2O,], L=15-crown-5 (n=1), 18-crown-6 (n=0). 6. ULCl2{X} , L=dicyclohexyl-18-crown-6, (X-= {BPh4}), L=cryptate-222 (X-={PF6}). 6 7. Adducts of uncertain stoichiometry were obtained when L was a mono-dentate amide, O, O', O'',O'''-tetraethyltrimethylenediphosphonate or 18-crown-6 with {BPh4-} or {PF6-} counteranion; and dicyclohexyl-18-crown-6 or 222 with Cl- counteranion. The adducts were prepared from ethanolic solutions of the red double chloride, MUCl4. 5H2O (M+=NH4, Rb), and the appropriate ligand under anaerobic conditions. Infra-red spectroscopy implied that ligands were coordinated to U (III) via C=O, P=O or C-O-C oxygen atoms with {BPh 4} and {PF 6} non-coordinated. Adducts 1 probably contain 8-coordinate U(III) with lowering to C. N. =6 in adducts 2 explained by steric effects. U(III) probably occupies the crown ether and cryptate cavities, although a sandwich-type structure is proposed for 3. Adducts 4 may contain bridging ligands. The diffuse reflectance electronic spectra (200-2000nm) exhibited broad, intense absorptions at 6d, possibly metal-to-ligand charge transfer, and internal ligand and {BPh4-} transitions, and sharp, weak 5f 5f transitions at > 700nm, with little U(IV) impurity confirmed by the absence in most cases of a U(IV) band near 1500nm. Shifts in position of the 5f 6d band maxima are explained in terms of the nephelauxetic effect; shifts within series 1 and 2 adducts, and on comparing the spectra of adducts containing C=O, P=O and C-O-C groups, may be related to the donor strength of the ligand and interligand steric effects affecting U-0 bond covalency. The 5f --> 5f spectra were similar for most adducts, although changes observed for adduct 2b and the 18-crown-6 adducts may reflect changes in environment around U(III). The insoluble, dark-green adduct, HU{Fe(CN)6}. 9-10H2O, isolated by addition of K4 {Fe (CN)6}. 3H2O to an aqueous U(III) sulphate solution , may contain SO2- impurity and other stoichiometries are possible. Electronic and infra-red spectral evidence implied a U(III) -N interaction and a polymeric structure is suggested. The first single-crystal X-ray structure determination of an hydrated uranium (III) compound, NH4U(SO4)2. 4H2O, is reported. It is monoclinic, P2 1/c. The structure, solved by Patterson and Fourier methods and refined to R=9. 6%, contains U coordinated to 9 oxygen atoms, 6 from 4 sulphate groups and 3 from H2O molecules (U-O = 2. 376-2. 595A) arranged in a polyhedron intermediate between a tricapped trigonal prism and a monocapped square antiprism. U atoms are linked into sheets parallel to (010) via sulphate bridges with adjacent sheets probably held together by hydrogen bonds. U2 (SO4)3. 9H2O is isomorphous with La2(SO4)3. 9H2O (powder photography) and contains one U (III). 12-coordinate to oxygen atoms (icosahedron) from 6 SO4 groups, and a second U(III) 9-coordinate (tricapped trigonal prism) to 6 H2O (apical) and 3 SO4 (equatorial) oxygen atoms.