Synthesis,Crystal Structures,and Optical Properties of Two New Layered Quaternary Tantalum Thiophosphates and the Thermal Conversion of Cs_4Ta_4P_4S_24 into Cs_2Ta_2P_2S_12

摘要

The reaction of Ta with an in situ formed polythiophosphate melt of Cs_2S_3,P_2S_5,and S yields the two new quaternary tantalum thiophosphates Cs_2Ta_2P2S_12(I)and Cs_4Ta_4P_4S_24(II).Both compounds were obtained with the same stoichiometric ratio but at different reaction temperatures.Compound I was prepared at 873 K and crystallizes in the monoclinic space group P2_1/c(No.14)with a=8.862(2)A,b=12.500(3)A,c=17.408(4)A,beta=99.23(3)deg,and Z=4.Compound II was prepared at 773 K and crystallizes in the monoclinic space group P2_1(No.14)with a=14.298(3)A,b=17.730(4)A,c=16.058(3)A,beta=106.19(3)deg,and Z=4.The two structures are closely related and exhibit two-dimensional anionic layers consisting of dimeric[Ta_2S_11]units which are linked by two tetradentate and two tridentate[PS_4]tetrahedra.The significant difference between these two compounds is the orientation of the[Ta_2S_11]units in infinite[Ta_2S_4(PS_4)]_x chains which are subunits of both structures.The specific orientation of the[Ta_2S_11]blocks in compound I leads to the formation of one cavity in the ~1 _propor.to[Ta_2P_2S_12]~2- layers,whereas in compound II two types of cavities are observed in the ~2 _propor.to[Ta_4P_4S_24]~4- layers.The Cs~+ ions are located between the layers above and below the cavities.The compounds were characterized with infrared spectroscopy in the MIR region,Raman spectroscopy,and UV/Vis diffuse reflectance spectroscopy.When Cs_4Ta_4P_4S_24(II)is heated at the synthesis temperature of compound I it is fully converted into compound I.