Empirical Formula: C₁₀H₁₀Ni
Molecular Weight: 188.8798 
EINECS: 215-039-0 
Enthalpy of Vaporization: 27.4 kJ/mol
Boiling Point: 41.5 °C at 760 mmHg
Vapour Pressure: 418 mmHg at 25 °C
Melting point: 171-173 °C(lit.)
Storage tempreture: 2-8 °C
Sensitive: Air & Moisture sensitive
Appearance: Bright green paramagnetic solid
Solubility: Dark liquid in an 8-10% solution in toluene, insoluble in water
Structure of Nickelocene (CAS NO.1271-28-9):
                        
IUPAC Name: Cyclopenta-1,3-diene ; Nickel(2+)
Canonical SMILES: [CH-]1C=CC=C1.[CH-]1C=CC=C1.[Ni+2]
InChI: InChI=1S/2C5H5.Ni/c2*1-2-4-5-3-1;/h2*1-5H;/q2*-1;+2
InChIKey: KZPXREABEBSAQM-UHFFFAOYSA-N
Product Category of Nickelocene (CAS NO.1271-28-9): Metallocenes;Ni (Nickel) Compounds;Transition Metal Compounds

 Nickelocene (CAS NO.1271-28-9), which was first prepared by E. O. Fischer in 1953, shortly after the discovery of ferrocene, has been prepared in a one-pot reaction, by deprotonating cyclopentadiene with ethylmagnesium bromide, and adding anhydrous nickel(II) acac.

NTP 10th Report on Carcinogens. IARC Cancer Review: Group 1 IMEMDT    IARC Monographs on the Evaluation of Carcinogenic Risk of Chemicals to Man . 7 ,1987,p. 264.(World Health Organization, Internation Agency for Research on Cancer,Lyon, France.: ) (Single copies can be ordered from WHO Publications Centre U.S.A., 49 Sheridan Avenue, Albany, NY 12210) ; Animal Sufficient Evidence IMEMDT    IARC Monographs on the Evaluation of Carcinogenic Risk of Chemicals to Man . 11 ,1976,p. 75.(World Health Organization, Internation Agency for Research on Cancer,Lyon, France.: ) (Single copies can be ordered from WHO Publications Centre U.S.A., 49 Sheridan Avenue, Albany, NY 12210) ; Animal Inadequate Evidence IMEMDT    IARC Monographs on the Evaluation of Carcinogenic Risk of Chemicals to Man . 2 ,1973,p. 126.(World Health Organization, Internation Agency for Research on Cancer,Lyon, France.: ) (Single copies can be ordered from WHO Publications Centre U.S.A., 49 Sheridan Avenue, Albany, NY 12210) . Nickel and its compounds are on the Community Right-To-Know List. Reported in EPA TSCA Inventory.

Confirmed carcinogen with experimental carcinogenic, neoplastigenic, and tumorigenic data. Poison by intraperitoneal and intramuscular routes. Moderately toxic by ingestion. When heated to decomposition it emits acrid smoke and irritating fumes. See also NICKEL COMPOUNDS.
Hazard Codes: F,T
Risk Statements: 49-11-22-43
R11:Highly flammable. 
R22:Harmful if swallowed. 
R43:May cause sensitization by skin contact. 
R49:May cause cancer by inhalation.
Safety Statements: 53-36/37/39-45 
S36/37/39:Wear suitable protective clothing, gloves and eye/face protection. 
S45:In case of accident or if you feel unwell, seek medical advice immediately (show the label whenever possible.) 
S53:Avoid exposure - obtain special instructions before use.

 Nickelocene , its cas register number is 1271-28-9. It also can be called Nickel, compd with pi-cyclopentadienyl (1:2) ; pi-Cyclopentadienyl compd. with nickel ; and Nickel biscyclopentadiene . It is of enduring academic interest, although it yet has no practical applications. Nickelocene (CAS NO.1271-28-9) belongs to a group of organometallic compounds called metallocenes that usually adopt sandwich structures in which a metal ion is sandwiched between two parallel cyclopentadienyl rings, a structure which not only confers stability but also solubility in organic solvents and volatility.
 It is hazardous, so the first aid measures and others should be known. Such as: When on the skin: first, should flush skin with plenty of water immediately for at least 15 minutes while removing contaminated clothing. Secondly, get medical aid. Or in the eyes: Flush eyes with plenty of water for at least 15 minutes, occasionally lifting the upper and lower eyelids. Then get medical aid soon. While, it's inhaled: Remove from exposure and move to fresh air immediately. Give artificial respiration while not breathing. When breathing is difficult, give oxygen. And as soon as to get medical aid. Then you have the ingesting of the product: Wash mouth out with water, and get medical aid immediately.
In addition, Nickelocene (CAS NO.1271-28-9) may decompose on exposure to air. It is not compatible with strong oxidizing agents, ignition sources, and you must not take it with incompatible materials. And also prevent it to broken down into hazardous decomposition products: carbon monoxide, carbon dioxide.