Synthesis and Crystal Structure of Trigadolinium Bromoorthosilicate，Gd_3Br（SiO_4）_2

ＳｙｎｔｈｅｓｉｓａｎｄＣｒｙｓｔａｌＳｔｒｕｃｔｕｒｅｏｆＴｒｉｇａｄｏｌｉｎｉｕｍＢｒｏｍｏｏｒｔｈｏｓｉｌｉｃａｔｅ，Ｇｄ_３Ｂｒ（ＳｉＯ_４）_２ＭａｏＪｉａｎｇ－Ｇａｏ；ＺｈｕａｎｇＨｏｎｇ－Ｈｕｉ；ＨｕａｎｇＪｉｎ－Ｓｈｕｎ（ＳｔａｔｅＫｅ?..

Synthesis and Crystal Structure of Trigadolinium Bromoorthosilicate, Gd_3Br(SiO_4)_2

Crystals of a new lanthanide orthosilicate, Gd_3Br(SiO_4)_2 (M_r=735.82) were prepared by solid state reaction from the GdOBr/V/NH_4Br system at 900℃. The ammonium bromide served as transport gas. The title compound crystallizes on orthorhombic, space group Imma with a=6.960(3), b=18. 176(6), c=6. 284(2) A ; V=794. 9(5) A￣3; Z=4; D_c=6. 12 g/cm￣3 F(000)=1276; μ(MoKα)=301.63cm￣(-1). A full-matrix least-squares structure factors refined with the 484 observed reflections with I>3. 0σ (I) and anisotropic thermal parameters for the Gd atoms gave R=0.061 and R_w=0. 064 respectively. The gadolinium atoms are in two sites and 8-coordinated as GdO_6Br_2 and GdO_7Br bicapped trigonal prism. The Gd(2) atom is disordered and distributed systematically among two I-lattice related(81) positions, the distance between these positions is 1.599 A. The presence of the bromine atoms causes some long Gd - O bonds. The silicon atoms were extracted from the quartz tube.