TCP, a new quasi-one-dimensional conducting platinate: DC and NMR studies

Cs$_{4}$[Pt(CN)$_{4}$](CF$_{3}$SO$_{3})_{2}$, or TCP, is the newest member of the family of quasi-one-dimensional conducting platinates that includes the widely studied K$_{2}$[Pt(CN)$_{4}$]Br$_{0.30}$3(H$_{2}$O) (KCP) -- best-known for its metal-insulator transition consistent with a Peierls instability. Unlike KCP, however, we have found properties unique to TCP. X-ray diffraction shows longer Pt-Pt separations, and undergoes subtle change with cooling. DC resistivity measurements presented technical challenges that had to be resolved, but in the end revealed a more highly insulating phase at room temperature, and the temperature dependence of resistivity has an anomalous ``peak'' at around 150 K. NMR also presented a technical challenge in that the $^{195}$Pt nucleus, which had been successfully used for NMR studies on KCP, did not produce a usable signal in TCP, wherein we utilized the peripheral $^{133}$Cs nuclei instead. Quadrupole splitting of spin states of $^{133}$Cs measured as a function of orientation showed consistency with the angular dependence expected of the known symmetry axes of $^{133}$Cs. Preliminary measurements of longitudinal relaxation time T1 also reveal an anomalous temperature dependence in the vicinity of 150 K. All these considerations point to a possible structural transformation, as will be discussed.