Ni_(2)M^(Ⅱ)Te^(Ⅳ)_(2)O_(2)(PO_(4))_(2)(OH)_(4)(M^(Ⅱ)=Ni,Zn):Synthesis,Crystal Structure,and Magnetic Properties

摘要

Two isostructural tellurite phosphates Ni_(2)M^(Ⅱ)Te^(Ⅳ)_(2)O_(2)(PO_(4))_(2)(OH)_(4)(M^(Ⅱ)=Ni,Zn)have been synthesized via hydrothermal method.Both of them crystalize in monoclinic space group C2/m(No.12).For Ni_(2)ZnTe^(Ⅳ)_(2)O_(2)(PO_(4))_(2)(OH)_(4),a=19.3247(10),b=5.9697(3),c=4.7737(2)Å,β=103.637(5)°,V=535.18(5)Å^(3),Z=2,M_(r)=727.94,S=1.103,D_(c)=4.517 g·cm^(-3),μ(Mo Kα)=11.434 mm^(-1) and F(000)=672,the final R=0.0369and wR=0.1086 for 639 observed reflections with I>2σ(I).The crystal structure of Ni_(2)M^(Ⅱ)Te^(Ⅳ)_(2)O_(2)(PO_(4))_(2)(OH)_(4)(M^(Ⅱ)=Ni,Zn)features a 3D framework composed of[Ni_(2)O_(2)(PO_(4))_(2)]^(6-)layers interconnected by[MTe_(2)O_(2)(OH)_(4)]^(2+)single chains.Different magnetic susceptibility results at low temperature of the two title compounds confirm that Zn(1)completely occupies the Ni(2)position but not partially substitutes both Ni(1)and Ni(2)position atoms.Additionally,the acentric TeO_(3)(OH)_(2) tetragonal pyramids are aligned in an antiparallel manner,resulting in the crystallization of centrosymmetric(C2/m)crystal structure instead of the non-centrosymmetric crystal structure.The investigation of the origin of centrosymmetric crystal structure with strong dipole moment units provides deeper understanding for future rational design for non-centrosymmetric crystal structure.