NMR study of $^{133}$Cs in new quasi-one-dimensional conducting platinate

Cs$_{4}$[Pt(CN)$_{4}$](CF$_{3}$SO$_{3})_{2}$ (TCP) is a new Krogmann's salt, consisting of quasi-one-dimensional conducting chains of Pt with well known properties, especially in the potassium-containing material, KCP. Unlike KCP, however, there are properties unique to TCP, e.g., longer Pt-Pt separation, insulating at room temperature, and non-magnetic. Previous NMR studies on KCP have mainly been on $^{195}$Pt, which does not produce a usable NMR signal in TCP; our study utilizes $^{133}$\textbf{Cs} instead, which are peripheral to the Pt chains. Splitting of spin states due to quadrupole interaction with local electric field gradient has been measured as a function of orientation versus applied static field. Modeling of the frequency shifts reveals consistency with the known symmetry axes of $^{133}$\textbf{Cs} determined by single-crystal x-ray diffraction. Relaxation time T1 versus temperature reveals a weak relaxation mechanism and absence of magnetism. Relaxation data has a sharp anomaly around 119 K where T1 jumps 3 orders of magnitude, consistent with critical fluctuations but not yet well understood.