[Catherine S.P]

If for example you have the complex [Cu(NH3)(OH2)]2+, you can make various mer and fac isomers when regarding each ligand NH3 and OH2, do you count each different arrangement of OH2 and NH3 as seperate isomers or do you just do one isomer for fac and one isomer for mer arrangement?

I hope this makes sense :S

[enahs]

Could you distinguish the two different meridional isomers?

[cheese (MSW)]

fac (facial, all cis, on one face) and mer (meridional, two cis, one trans, A3 around a meridian) is reserved for octahedral cmplxs of the type MA3B3 and
there is only one isomer of each (make a model).  Your cmplx should .: be [Cu(H2O))3(NH3)3]^2+; go from there (neglect J-T distortion).
MA5B: one isomer; MA4B2 cis and trans, Ma3B3 fac and mer; MA3B2C: fac, mer-cis, mer trans;  A and B
monodentate ligands; M(L-L)3 and cis-M(L-L)2X2: Δ(R); Λ(L) should get you through your first course in TM coordination chem.