INFRARED-SPECTRA OF M(3)(I)M(III)S(3) TYPE SYNTHETIC MINERALS (M(I)=TL OR AG, M(III)=AS OR SB)

The infrared spectra of four compounds of the M(3)(I)M(III)S(3) type w ith M(I) = Tl or Ag, and M(III) = As or Sb were studied at room temper ature (RT) and at the boiling temperature, respectively, of liquid nit rogen (LNT). The contribution of the Ag-S coordinates to the vibration al modes producing the infrared bands in the spectra of the silver com pounds is more pronounced than that of the Tl-S coordinates in the cor responding thallium compounds. This conclusion is in line with the mor e pronounced covalent character of the Ag-S bonds as compared with the Tl-S ones.