Low-Frequency Sub-Terahertz Absorption in Hg II -XCN-Fe II (X=S, Se) Coordination Polymers.

Self-assembly Fe II complexes of phenazine (Phen), quinoxaline (Qxn), and 4,4'-trimethylenedipyridine (Tmp) with tetrahedral building blocks of [Hg II (XCN) 4 ] 2- (X=S or Se) formed six new high-dimensional frameworks with the general formula of [Fe(L) m ][Hg(XCN) 4 ]⋅solvents (L=Phen, m/X=2/S, 1; L=Qxn, m/X=2/S, 2; L=Qxn, m/X=1/S, 3; L=Qxn, m/X=1/Se, 3-Se; L=Tmp, m/X=1/S, 4; and L=Tmp, m/X=1/Se, 4-Se). 1, 3, and 3-Se show an intense sub-terahertz (sub-THz) absorbance of around 0.60 THz due to vibrations of the solvent molecules coordinated to the Fe II ions and crystallization organic molecules. In addition, crystals of 1, 4, and 4-Se display low-frequency Raman scattering with exceptionally low values of 0.44, 0.51, and 0.53 THz, respectively. These results indicate that heavy metal Fe II -Hg II systems are promising platforms to construct sub-THz absorbers.