In its pure form, the formula is Ni(ClO 4 ) 2 ..
If purchased commercially, it will most likely come in its hexahydrate form (Nickel(II) Perchlorate Hexahydrate): Ni(ClO 4 ) …2 .6H 2 O.
It's flammable, carcinogenic and explosive under conditions of fire and mechanical shock. Is also a sensitiser of, and harmful to, the skin and eyes. Take particular care with this compound..
Ref: http://www.sigmaaldrich.com/catalog/ProductDetail.do?N4=309338|ALDRICH&N5=SEARCH_CONCAT_PNO|BRAND_KEY&F=SPEC# (MORE)