Mercury and its compounds are on the Community Right-To-Know List. NESSLER REAGENT  is reported in EPA TSCA Inventory.

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)
DOT Classification:  6.1; Label: Poison

The Nessler reagent with CAS registry number of 7783-33-7 is also called Mercuric potassium iodide. The IUPAC name is dipotassium tetraiodomercury(2-). Its EINECS registry number is 231-990-4. In addition, the molecular formula is HgI₄K₂ and the molecular weight is 786.40. It is a kind of light yellow liquid and belongs to the class of Inorganics.

Physical properties about Nessler reagent are: (1)H-Bond Acceptor: 1; (2)Rotatable Bond Count: 0; (3)Exact Mass: 787.515912; (4)MonoIsotopic Mass: 787.515912; (5)Topological Polar Surface Area: 0; (6)Heavy Atom Count: 7; (7)Formal Charge: 0; (8)Complexity: 19.1; (9)Covalently-Bonded Unit Count: 3.

When you are using this chemical, please be cautious about it as the following:
This chemical has danger of cumulative effects and can cause severe burns. And it is very toxic by inhalation or prolonged exposure, in contact with skin and if swallowed. In addition, it is very toxic to aquatic organisms, and may cause long-term adverse effects in the aquatic environment. You can refer to special instructions safety data sheet. During using it, wear suitable protective clothing, gloves and eye/face protection. In case of contact with eyes, rinse immediately with plenty of water and seek medical advice. And in case of accident or if you feel unwell, seek medical advice immediately (show label where possible). What's more, you should keep it away from food, drink and animal feeding stuffs. And you should avoid release to the environment. This material and its container must be disposed of as hazardous waste.

You can still convert the following datas into molecular structure:
(1)SMILES: [K+].[K+].I[Hg-2](I)(I)I
(2)InChI: InChI=1/Hg.4HI.2K/h;4*1H;;/q+2;;;;;2*+1/p-4/rHgI4.2K/c2-1(3,4)5;;/q-2;2*+1
(3)InChIKey: OPCMAZHMYZRPID-SXSZOQDCAN

The toxicity data is as follows:

Organism	Test Type	Route	Reported Dose (Normalized Dose)	Effect	Source
guinea pig	LDLo	intraperitoneal	1gm/kg (1000mg/kg)		Archives of Environmental Health. Vol. 11, Pg. 201, 1965.
guinea pig	LDLo	skin	1gm/kg (1000mg/kg)		Archives of Environmental Health. Vol. 11, Pg. 201, 1965.