THE SYNTHESES, CRYSTAL AND MOLECULAR-STRUCTURES, AND THEIR THERMAL-PROPERTIES OF TETRAMETHYLAMMONIUM [OCTAKIS(ISOTHIOCYANATO)LANTHANOIDATES(III)].BENZENE (1/2), [(CH3)4N]5[M(NCS)8].2C6H6(M=LA, CE, PR, ND, SM, EU, GD, TB, DY)

The titled series of isomorphous complexes, the first octakis(isothiocyanato) complexes of lanthanoids, were obtained. Their crystals are tetragonal, space group P4nc, Z=2. The cell dimensions of the praseodymium complex, for example, are a=15.871(7), c=11.543(6) Å, U=2908(3) Å3, and D(m)=1.29(3), D(x)=1.29 g cm-3, μ(Mo Kα)= 11.60 cm-1, with a final R value of 0.069. The metal atom is octa-coordinated by eight isothiocyanate ions in an intermediate geometry between cube and square-antiprism. The benzene included in the praseodymium complex crystals was retained up to 174°C (DTA), and was not removed even after being heated for 12 h at 110°C. In cases of the other isomorphous members, the benzene was removed at lower temperatures, respectively. The isomorphous fluorobenzene adduct was obtained only for the lanthanum complex.