IUPAC:  Diiodomercury
 Mercury(II) iodide (7774-29-0) is also called for  EINECS 231-873-8 ; HSDB 1211 ; Hydrargyrum bijodatum ; Hydrargyrum diodatum ; Mercuric iodide ; Mercuric iodide, red ; Mercurius bijodatus ; Mercury biniodide ; Mercury diiodide ; Mercury iodide (HgI2) ; Red mercuric iodide ; alpha-Mercury(II) iodide and so on.
Molecular Formula: HgI₂
Molecular Weight: 454.4
EINECS: 231-873-8
Enthalpy of Vaporization: 19.76 kJ/mol 
Boiling Point: 127°C at 760 mmHg 
Vapour Pressure: 13.8 mmHg at 25°C 
Heavy Atom Count: 3
Formal Charge: 0
Complexity: 2.8
Isotope Atom Count: 0
Defined Atom StereoCenter Count: 0
Undefined Atom StereoCenter Count: 0
Defined Bond StereoCenter Count: 0
Undefined Bond StereoCenter Count: 0
Covalently-Bonded Unit Count: 1 
The appearance of  Mercury(II) iodide (7774-29-0)  is red-orange crystal.
The molecular structure of  Mercury(II) iodide (7774-29-0):

1.In medicine, Mercury(II) iodide (7774-29-0) is formerly used as a treatment for syphilis.
2.In veterinary medicine, Mercury(II) iodide (7774-29-0) is used in blister ointments in exostoses, bursal enlargement and so on.
3. Mercury(II) iodide (7774-29-0) is used for preparation of  Nessler's reagent, used for detection of  presence of  ammonia.
4. Mercury(II) iodide (7774-29-0) is a semiconductor material, used in some x-ray and gamma ray detection and imaging devices operating at room temperatures.

Mercury and its compounds are on the Community Right-To-Know List. Reported in EPA TSCA Inventory.

A human poison by ingestion. Poison experimentally by ingestion, skin contact, and intraperitoneal routes. An experimental teratogen. Violent reaction with chlorine trifluoride. When heated to decomposition it emits very toxic fumes of Hg and I⁻. See also MERCURY COMPOUNDS, INORGANIC; MERCURY COMPOUNDS, ORGANIC and IODIDES.
Hazard Codes:  T+ ,N 
Risk Statements:  26/27/28-33-50/53 
R26/27/28:Very toxic by inhalation, in contact with skin and if swallowed. 
R33:Danger of cumulative effects. 
R50/53:Very toxic to aquatic organisms, may cause long-term adverse effects in the aquatic environment.
Safety Statements:  13-28-45-60-61 
S13:Keep away from food, drink and animal foodstuffs. 
S28:After contact with skin, wash immediately with plenty of soap-suds. 
S45:In case of accident or if you feel unwell, seek medical advice immediately (show the label whenever possible.) 
S60:This material and its container must be disposed of as hazardous waste. 
S61:Avoid release to the environment. Refer to special instructions / safety data sheets.
RIDADR:  UN 2025 6.1/PG 2
WGK Germany:  3
RTECS:  OW5250000
F:  8
HazardClass:  6.1
PackingGroup:  II

OSHA PEL: CL 0.1 mg(Hg)/m³ (skin)
ACGIH TLV: TWA 0.1 mg(Hg)/m³ (skin); BEI: 35 µg/g creatinine total inorganic mercury in urine preshift; 15 µg/g creatinine total inorganic mercury in blood at end of shift at end of workweek.
NIOSH REL: (Mercury, Aryl and Inorganic) CL 0.1 mg/m³ (skin)

1.Reactivity Profile
 Mercury(II) iodide (7774-29-0) is a mild reducing agent. Reacts with sodium azide to form mercury(II) azide, which is shock, friction, and heat sensitive. Incompatible with acetylene, ammonia, chlorine dioxide, azides, chlorine trifluoride, calcium (because of amalgam formation), sodium carbide, lithium, rubidium, copper .