SYNTHESIS, MAGNETIC-SUSCEPTIBILITY AND X-RAY CRYSTAL-STRUCTURE OF ((T)BUNCHCHN(T)BU)(3)YB

The reaction of (C10H8)Yb(THF)(3) with (t)BuN=CHCH=N(t)Bu ((t)Budad) in tetrahydrofuran at room temperature leads to Yb((t)Budad)(3) (1), which is also obtained from the reaction of YbCl3 and three molar equivalents of K((t)Budad) in tetrahydrofuran or by metal vapor synthesis. 1 has been characterized by X-ray diffraction. The crystals are monoclinic, space group C2, Z = 2 with a = 1034.8(9), b = 1710.4(6), c = 1020.4(8) pm, beta = 113.28(2)degrees. The structure was refined to R = 0.0274 for 1466 observed reflections (F-o > 4 sigma(F-o)). The structure shows that the empirical composition is Yb((t)Budad), and that the coordination number of Yb is six, but the X-ray data are not sufficiently accurate to judge if the oxidation state of ytterbium is zero, two or three. The magnetic susceptibility of solid 1, prepared by metal vapor synthesis, was studied from 5 to 300 K. The magnetic results are explained by postulating that the bivalent ytterbium species [Yb-II((t)Budad(-)),((t)Budad)] predominates at low temperature and as the temperature increases the trivalent ytterbium species [Yb-III((t)Budad(-))(3)] predominates in the solid state.