TRIS(TRIMETHYLSILYL)SILOXIDES OF GADOLINIUM AND LANTHANUM : SYNTHESIS, STRUCTURE AND SOME PROPERTIES

Abstract A series of gadolinium and lanthanum siloxide complexes of empirical formula [(Me 3 Si) 3 SiO] 3 Ln(L n ) {Ln=Gd, L n =(THF) 2 ( 1 ), (MeCN) 2 ( 2 ), [N(C 2 H 4 ) 3 N] 2 ( 3 ), (4,4′-dipyridyl) 2 ( 4 ), (4,4′-dipyridyl) 1 ( 5 ); Ln=La, L n =(THF) 4 ( 6 )} have been prepared by the reaction of [(Me 3 Si) 2 N] 3 Ln (Ln=Gd, La) with (Me 3 Si) 3 SiOH or LnCl 3 (Ln=Gd) with (Me 3 Si) 3 SiONa in various solvents. Both [(Me 3 Si) 3 SiO] 3 Gd(THF) 2 ( 1 ) and [(Me 3 Si) 3 SiO] 3 Gd[N(C 2 H 4 ) 3 N] 2 ( 3 ) have been characterized by X-ray crystallography. The Gd in both 1 and 3 has a trigonal-bipyramidal environment with three O atoms in equatorial and two B atoms (B=O in 1 and N in 3 ) in axial positions. The symmetries of molecules of 1 and 3 are C 3 i and C 3 h , respectively. The GdOSi angles and the GdO distances are 161.2(3)°, 2.142(7) A in 1 and 165.4(2)°, 2.161(4) A in 3 . The GdO(THF) distances in 1 are 2.448(9), 2.314(18) and the GdN distance in 3 is 2.520(6) A. Gadolinium complex ( 1 ) and the lanthanum complex ( 6 ) readily absorb one and three moles of CO 2 , respectively to form the corresponding carbonates. Compounds 1 and 6 sublime at 205°C in vacuo to form homoleptic siloxides. A subsequent rise in temperature results in their decomposition to give polylanthanosiloxanes, and (Me 3 Si) 3 SiOH as the only volatile product up to 300°C.