IUPAC Name: 1H-pyrazolo[3,4-d]pyrimidin-4-amine 
Empirical Formula: C₅H₅N₅
Molecular Weight: 135.1267g/mol
EINECS: 219-174-6 
Structure of 4H-Pyrazolo[3,4-d]pyrimidin-4-amine (CAS NO.20289-44-5):

Index of Refraction: 1.837
Molar Refractivity: 37.03 cm³
Molar Volume: 83.8 cm³
 Polarizability: 14.68 10^-24cm³
Surface Tension: 122.7 dyne/cm
Density: 1.612 g/cm³
Flash Point: 244.4 °C
Enthalpy of Vaporization: 68.67 kJ/mol
Boiling Point: 431.1 °C at 760 mmHg
Vapour Pressure: 1.23E-07 mmHg at 25°C 
Product Categories: PYRIMIDINE;Pyridines, Pyrimidines, Purines and Pteredines;Amines;Pyrimidines;Fused Ring Systems;Building Blocks;Heterocyclic Building Blocks 
Canonical SMILES: C1=NNC2=C1C(=NC=N2)N
InChI: InChI=1S/C5H5N5/c6-4-3-1-9-10-5(3)8-2-7-4/h1-2H,(H3,6,7,8,9,10)
InChIKey: LHCPRYRLDOSKHK-UHFFFAOYSA-N

Hazard Codes: T
Risk Statements: 25-36/37/38-23/24/25 
R25 :Toxic if swallowed. 
R36/37/38:Irritating to eyes, respiratory system and skin. 
R23/24/25:Toxic by inhalation, in contact with skin and if swallowed.
Safety Statements: 26-36/37/39-45-22 
S26: In case of contact with eyes, rinse immediately with plenty of water and seek medical advice. 
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.) 
S22:Do not breathe dust.
RIDADR: UN 2811 6.1/PG 3
WGK Germany: 3
RTECS: UR0717000
HazardClass: 6.1(b)
PackingGroup: III

  4H-Pyrazolo[3,4-d]pyrimidin-4-amine , its cas register number is 20289-44-5. It also can be called 4-Aminopyrazolo(3,4-d)pyrimidine ; 1H-Pyrazolo(3,4-d)pyrimidin-4-amine . 4H-Pyrazolo[3,4-d]pyrimidin-4-amine (CAS NO.20289-44-5) is irritating to eyes, respiratory system and skin. And it's toxic by inhalation, in contact with skin and if swallowed.