Nickel has four oxidation states: Ni(I), Ni(II), Ni(III), and Ni(IV).
Selenium is a group 6 non-metal...so it's oxidation state is -2.
Therefore, you can have four possible formulas for nickel selenide:
Ni2Se, NiSe, Ni2Se3, and NiSe2.
However, the three most commonly found are:
NiSe, Ni2Se3, and NiSe2.
Formula: NiSe
NiSe
titanium (II) selenide = SeTi
Nickel(II)Selenide
V2Se5 is the formula for vanadium V selenide.
Formula: Co2Se3
Rubidium selenide has the formula Rb2Se.
titanium (II) selenide = SeTi
Nickel(II)Selenide
V2Se5 is the formula for vanadium V selenide.
Formula: Co2Se3
The formula for nickel(II) iodide is NiI2.
Almost certainly you are looking for Titanium(IV) Selenide, TiSe2, though the Titanium(III) compound, Ti2Se3 may exist as well. You should be more specific :)
Rubidium selenide has the formula Rb2Se.
Formula: Cs2Se
the formula is NiCl2
Tin(IV) selenide
Ni2P2O7
NiBr2