Synthesis and Characterization of Heavier Dioxouranium(VI) Dihalides

Abstract

The synthesis and characterization of the dioxouranium(VI) dibromide and iodide hydrates, UO(2)Br(2)x3H(2)O (1), [UO(2)Br(2)(OH(2))(2)](2) (2), and UO(2)I(2)x2H(2)Ox4Et(2)O (3), are reported. Moreover, adducts of UO(2)I(2) and UO(2)Br(2) with large, bulky OP(NMe(2))(3) and OPPh(3) ligands such as UO(2)I(2)(OP(NMe(2))(3))(2) (4), UO(2)Br(2)(OP(NMe(2))(3))(2) (5), and UO(2)I(2)(OPPh(3))(2)(6) are discussed. The structures of the following compounds were determined using single-crystal X-ray diffraction techniques: (1) monoclinic, P2(1)/c, a = 9.7376(8) A, b = 6.5471(5) A, c = 12.817(1) A, beta = 94.104(1) degrees , V = 815.0(1) A(3), Z = 4; (2) monoclinic, P2(1)/c, a = 6.0568(7) A, b = 10.5117(9) A, c = 10.362(1) A, beta = 99.62(1) degrees , V = 650.5(1) A(3), Z = 2; (4) tetragonal, P4(1)2(1)2, a = 10.6519(3) A, b = 10.6519(3) A, c = 24.0758(6) A, V = 2731.7(1) A(3), Z = 4; (5) tetragonal, P4(1)2(1)2, a = 10.4645(1) A, b = 10.4645(1) A, c = 23.7805(3) A, V = 2604.10(5) A(3), Z = 4, and (6) monoclinic, P2(1)/c, a = 9.6543(1) A, b = 18.8968(3) A, c = 10.9042(2) A, beta =115.2134(5) degrees , V = 1783.01(5) A(3), Z = 2. Whereas 1 and 2 are the first UO(2)Br(2) hydrates and the last missing members of the UO(2)X(2) hydrate (X = Cl --> I) series to be structurally characterized, 4 and 6 contain room-temperature stable U(VI)-I bonds with 4 being the first structurally characterized room temperature stable U(VI)-I compound which can be conveniently prepared on a gram scale in quantitative yield. The synthesis and characterization of 5 using an analogous halogen exchange reaction to that used for the preparation of 4 is also reported.

Convenient syntheses of uranyl(VI) cis-dihalide complexes as anhydrous starting materials

“…Uranyl(VI) halides commonly form six-coordinate complexes of the general formula UO 2 X 2 L 2 , where L is a neutral ligand that serves to cap the uranium coordination sphere. These complexes overwhelmingly occur as the trans isomer (A; Chart 1); of the few structurally characterized examples in which the two halide ligands are situated at adjacent equatorial sites, these compounds are either hydrated [2] (or possess ligands L with terminal O-H groups) [3,4], suffer from poor solubility [5], or have been obtained in unspecified yield from non-uranyl precursors [6]. Given the synthetic importance of stereochemical control in metal halide systems, a rational methodology to anhydrous uranyl(VI) cis-dihalide complexes that can serve as suitable starting materials with reagents in nonprotic solvents remains an unrealized goal.…”

“…A thermal ellipsoid drawing of 2a is shown in Fig. 1 along with selected bond distances and bond angles; a thermal ellipsoid drawing for the bromide derivative 3a is shown in Figure S1 The interatomic U@O, U-O (amide) [19,20] and U-N (pyridyl) [21] bond distances are all within the normal range for uranyl complexes, as are the respective U-Cl [22][23][24] and U-Br [2,5,25] These are the widest angles between adjacent equatorial ligands in these complexes; for comparison, reflecting the steric congestion that these large atoms place upon the remainder of the equatorial region, the most acute angle is that between N(1)-U(1)-O(2), at 61.48(7) in 2a and 61.04(17)°i n 3a. Possible steric strain induced by the crowded equatorial coordination sphere is evident in the conformation of the tridentate ligand, where the pyridyl ring is tilted approximately 30°with respect to the equatorial plane in both structures.…”

Crystal Chemistry of Uranyl Halides Containing Mixed (UO2)(XmOn)5 Bipyramids (X = Cl, Br): Synthesis and Crystal Structure of Cs2(UO2)(NO3)Cl3

“…The UrX 2 O 3 (X = Cl, Br) isolated bipyramid with two chlorine anions in the equatorial plane (Fig. 2b) has previously been observed in (UO 2 )X 2 (H 2 O) 3 (X = Cl, Br) [9,10]. Tetragonal UrX 4 (X = Cl, Br) bipyramids with the uranyl cation coordinated by four equatorial halide anions (Fig.…”

Uranyl–halide complexation in N,N-dimethylformamide: halide coordination trend manifests hardness of [UO2]2+

“…The U-Br distance (2.89 Å) is also usually found in known compounds. 14,18,[34][35][36] Consequently, the formula of this 1 : 1 [UO 2 ] 2+ -Br − complex is concluded to be [UO 2 Br(DMF) 4 ] + .…”

“…The distances from U to O eq (2.41 Å) and Br (2.88 Å) are also consistent with those usually found in complexes with a similar composition, UO 2 Br 2 L 3 (L = H 2 O, tetrahydrofuran), in crystalline states. 34,35 Now, a question arises, what gives such a difference in the solvation number between the dichlorido and dibromido complexes? The largest contribution determining the coordination number should be the steric hindrance.…”