[Sleepy]

How can you tell this is a tetrahedral? Cis- [Co(en)₂ Cl₂]+
And that it is a optical isomer

[Blueshawk]

i am not sure what the cpd is exaclty     (+)-Cis-Co₂Cl₂

so      Cl             Cl        
            \           /
              Co--Co

this is what I am seeing with the Cis-isomer.  To be tetrahedral, Co would need two lone pairs of electrons.  Which I believe it does.  So it would look something like below. where  :  and ..  are lone pairs.

          Cl            Cl        
            \          /
          : --Co--Co-- :
             /          \
            ..           ..

The tetrahedral is formed between the Two Co's and one Cl and two lone pairs  like this:

                        Cl        
                       /
               Co--Co-- :    with all angles  120 degrees.
                        \
                         ..


The (+) if at the beginning of the name means it rotates ( I think + is clockwise) in polarized light.

I hope i did this right, cause I'm not sure about the cpd.  But you can also use HyperChem on the computers to find symmetry or structure.  I am not at home so I can't use HyperChem right now.

Hope this helps...and hope its right.

[shelanachium]

The complex is octahedral like all those of trivalent cobalt, not tetrahedral. Octahedral complexes are chiral (have optical isomers) if they contain three chelate rings as in [Co(oxalate)3]3-; or if there are two rings and the remaining groups are cis, as in cis [Co(ethylenediamine)2Cl2]+. If you build models this will become clear. Trans [Co(ethylenediamine)2Cl2]+ has both chelate rings in the same plane, therefore has a plane of symmetry and is not chiral.

[Blueshawk]

The complex is octahedral like all those of trivalent cobalt, not tetrahedral. Octahedral complexes are chiral (have optical isomers) if they contain three chelate rings as in [Co(oxalate)3]3-; or if there are two rings and the remaining groups are cis, as in cis [Co(ethylenediamine)2Cl2]+. If you build models this will become clear. Trans [Co(ethylenediamine)2Cl2]+ has both chelate rings in the same plane, therefore has a plane of symmetry and is not chiral.

so is Cis-[Co(ethylenediamine)2Cl2]+   the actual cpd.....boy it really helps to know what it is I was going to try and explain .  

[AWK]

For trans-isomer exchange one NH2-group and Cl. Both Cl and Both NH2 groups are in the plane. For enantiomer exchange NH2 groups in plane.  +1 charge is missing at Co!