A novel supramolecule [HgCl2(ptz)](2).HgCl2 (ptz = phenothiazine) with uncoordinated inorganic salt HgCl2 presented in a 1D chain was first prepared and then successfully applied as a new precursor in the preparation of submicrometer Hg2Cl2 rods. Single crystal X-ray analysis showed that the 1D chain structure is stabilized by hydrogen bonds between adjacent chains and the coordination mode of the ligand phenothiazine is unusual with large steric inhibition other than the chain directions. The results revealed that the particular chain structure plays a significant role in the formation of the Hg2Cl2 rods.