New amide complexes of uranium(IV) thiocyanate; the crystal structure of tetraisothiocyanatotris(NN,2-trimethylpropionamide-O)uranium(IV)
Abstract
The complexes U(NCS)4·xL [x= 4, L = EtCONMe2(dmpa) or Me2CHCONMe2(dmiba); x= 3, L = Me2CHCONMe2] and U(NCS)4·3Me3CCONMe2·MeCOMe have been prepared and their u.v.–visible and i.r. spectra are reported. The crystal and molecular structure of [U(NCS)4(dmiba)3] has been determined by the heavy-atom method from X-ray diffractometer data and refined by least squares to R 0.083 for 1 816 independent reflections. The crystal is monoclinic, space group P21/a, with Z= 4, a= 21.195(9), b= 15.155(8), c= 11.204(6)Å, and β= 102.99(10)°. The co-ordination geometry about the seven-co-ordinate uranium atom is pentagonal bipyramidal with two NCS groups in the axial positions, an unusual geometry for uranium(IV) species. The average bonding distances for U–O and U–N are 2.30 and 2.38 Å respectively.