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) i n tetrahydrofuran at room temperature leads to Yb((t)Budad)(3) (1), wh ich is also obtained from the reaction of YbCl3 and three molar equiva lents of K((t)Budad) in tetrahydrofuran or by metal vapor synthesis. 1 has been characterized by X-ray diffraction. The crystals are monocli nic, 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 co ordination number of Yb is six, but the X-ray data are not sufficientl y accurate to judge if the oxidation state of ytterbium is zero, two o r three. The magnetic susceptibility of solid 1, prepared by metal vap or synthesis, was studied from 5 to 300 K. The magnetic results are ex plained by postulating that the bivalent ytterbium species [Yb-II((t)B udad(-)),((t)Budad)] predominates at low temperature and as the temper ature increases the trivalent ytterbium species [Yb-III((t)Budad(-))(3 )] predominates in the solid state.