Ammonium hexabromomercurate(II) is a chemical compound with the chemical formula (NH4)4[HgBr6].
Heating of a mixture of mercury(II) bromide and ammonium bromide: The compound forms black crystals of tetragonal system, space group P4/mnc, cell parameters: a = 0.925560 nm, c = 0.88657 nm, Z = 2.
[2][3] At a temperature of 200 K, the compound enters a phase of the monoclinic system, space group P21/n.
At 250 K, it forms crystals of the orthorhombic system, space group Pnnm.
[4]