Thermal expansion of d10 dicyanometallate-based coordination polymers

The thermal expansion of several new d10, dicyanometallate-based coordination polymers was examined by powder and single-crystal X-ray diffraction. In isostructural KNi[Au(CN)2]3, KCd[M(CN)2]3, and In[M(CN)2]3 (M=Ag(I), Au(I)), extremely large positive and negative thermal expansion (PTE/NTE) coefficients were discovered. Weaker metallophilic interactions promote larger PTE and NTE. Similarly, the M[Au(CN)2]2 series (M=Mn, Fe, Co, Zn, Hg) showed sizeable PTE and NTE effects. HgCN(NO3) exhibited similar behaviour, but significantly smaller PTE/NTE coefficients than the Ag and Au systems. Hg(CN)2 demonstrated entirely (anisotropic) PTE, partly attributed to a new structural mechanism resembling rigid unit modes in metal oxides. Hg(CN)2 is one of the first cyanide-containing frameworks not showing NTE. This work has demonstrated that Ag(I) and Au(I) in coordination polymers drive large expansivity, and when coupled with flexible cyanide frameworks, can also yield large NTE.