Complexes of U(BH3CH3)4 with CH3OCH2CH2OCH3, (CH3)2NCH2CH2N(CH3)2, and CH3SCH2CH2SCH3 have been synthesized and their molecular structures determined by single-crystal X-ray diffraction. U(BH3CH3)4-CH3OCH2CH2OCH3 is tetragonal, P4/n, with a = 21.822 (8) Á, c = 7.681 (5) Á, Z = 8, d = 1.61 g/cm3, and R = 0.028 [F2 > 'ia{F2)]\ U(BH3C-H3)4-(CH3)2NCH2CH2N(CH3)2 is monoclinic, P2t/n, with a = 10.206 (4) k,b= 15.436 (6) A, c = 12.880 (5) A, ß = 92.25 (3) °, Z = 4,d = 1.54 g/cm3, and R = 0.029 (F2 > 3 ( 2)); U(BH3CH3)4-CH3SCH2CH2SCH3 is triclinic, PI, with a = 8.937 (4) k,b= 13.692 (4) A, c = 8.186 (3) k, a = 96.46 (4)°, ß = 97.64 (4)°, = 74.07 (4)°, Z = 2, d = 1.66 g/cm3, and R = 0.023 (F2 > 2a(F2)). With one exception, all BH3CH3 groups are coordinated to the uranium atoms by tridentate hydrogen bridges with a U-B bond distance of 2.55 ± 0.02 A. For the (CH3)2NCH2CH2N(CH3)2 complex one B atom is coordinated to the uranium atom through a bidentate hydrogen bridge with a U-B distance of 2.72 (2) A and a U-B-C angle of 142 (2)°.