CoCl6 does not exist.
Common oxidation states of cobalt include +2 and +3, so two different chlorides are possible: CoCl2 and CoCl3 but the last one is rare.
(CoF3 (Co(III)-fluoride) is a better possibillity to prove this oxidation state)
Maximum oxidation state is +5, though Cobalt can easily 'coordinate' with in total 6 coordinative groups (=CG) and negative ions: Co(CG)4Cl2 (a coordinative group migh be a < -N| >-atom group of ammonia, ethylenediamine or haemoglobin)
The chemical formula of Cobalt VI chloride is CoCl3.
CoCl is the formula of cobalt (I) chloride
CrS3 is the formula of chromium(VI) sulfide
Cobalt tetraoxosulphate (vi) ion
That would be chromium(IV) selenide with the formula CrSe2
CrO3 is Chromium(VI) oxide also called Chromium trioxide
The molecular formula for ruthenium IV phosphide is RuP, and for uranium VI nitride, it is UN2. The formula Se2Cl2 represents diselenium dichloride, and Ni2CO3 is nickel(II) carbonate.
CrS3 is the formula of chromium(VI) sulfide
The chemical forrmula of potassium heptaoxodichromate(VI) is K2Cr2O7. The systematic IUPAC name is potassium dichromate (VI).
it is same as ammonium sulphate, (NH4)2SO4
Cobalt tetraoxosulphate (vi) ion
Cobalt tetraoxosulphate (vi) ion
That would be chromium(IV) selenide with the formula CrSe2
The molecular formula for ruthenium IV phosphide is RuP, and for uranium VI nitride, it is UN2. The formula Se2Cl2 represents diselenium dichloride, and Ni2CO3 is nickel(II) carbonate.
Cobalt tetraoxosulphate (vi) ion
Rhodium (VI) Chloride
A name for this compound would be cobalt dinitride. Co forms nitrides, CoN, Co2N and Co2N3, the only one with ionic characteristics is Co2N3. I do not think CoN2 has been characterised. Certainly if it was it would be misleading to call it Cobalt(VI) nitride.
Cobalt(II) carbonate
sulfur(VI) chloride