Far-infrared single-crystal study of potassium tetrabromoplatinate(II)

It is shown from far-i.r. reflectance measurements on a single crystal of K2[PtBr4] that the internal modes ν2(A2u),-π(Pt–Br) and ν7(Eu),δ(Pt–Br) are almost accidentally degenerate at 128 and 129 cm–1 at 295 K and 129 and 133 cm–1 at 38 K. The lattice modes are in the order Eu > A2u > Eu. The principal values of the low-frequency dielectric constant are estimated to be 7.06 [ε(1)=ε(2)] and 4.20 [ε(3)].