Crystal structure and optical and magnetic properties of tetrakis(diethylamido)uranium(IV), a five-coordinate dimeric complex in the solid state

The volatile U(IV) compound U[N(C2H5)2]4 is dimeric in the solid state and exhibits an unusual and possibly unique five coordination about the U ion for an f series ion. The crystals are monoclinic, space group P21/n. At 230C a = 9.326 (4) A, b = 17.283 (8) A, c = 13.867 (6) A, β = 108.43 (5)0, and d/sub c/ = 1.65 g/cm3 for Z = 4. X-ray diffraction intensity data were collected by an automated diffractometer using graphite monochromated Mo Kα radiation. For 1809 reflections with F2 less than 2 sigma(F2), R1 = 0.035 and R2 = 0.031. The five-coordinate uranium atom is at the center of a distorted trigonal bipyramid of nitrogen atoms; two of these bipyramids share an edge to make a dimeric complex located on a center of symmetry. The nearest approach of the uranium atoms is 4.004 (1) A. The three nonbridging U--N distances average 2.22 (2) A whereas the bridging U--N distances are 2.46 and 2.57 A. The N--U--N and U--N--U angles in the central cluster are 74.4 (3) and 105.6 (3)0, respectively. The optical and proton magnetic resonance spectra of U[NEt2]4 at room temperature in various solvents are reported. Temperature-dependent magnetic susceptibility measurements on the solid show Curie--Weiss behavior from 10 to 1000K. Below 100K the susceptibility becomes temperature independent and there is no indication of magnetic ordering. A greater tendency in U amide chemistry toward oligomerization than in the d transition series is suggested