Consider a co-ordination compound (Z)=[M(a)(b)(c)(d)(e)(f)] where a, b, c, d, e, and f are monodentate ligands which themselves don’t exhibit any isomerism. How many total isomers exist for given compound Z?

The compound Z=[M(a)(b)(c)(d)(e)(f)] is an octahedral complex with six different monodentate ligands.

The isomerism in coordination compounds can be of two types: structural isomerism and stereoisomerism.

1. Structural Isomerism: It doesn't occur in this case because all ligands are monodentate and there is no possibility of linkage or coordination isomerism.

2. Stereoisomerism: It can be of two types - geometrical and optical isomerism.

   a. Geometrical Isomerism: It doesn't occur in this case because all ligands are different.

   b. Optical Isomerism: It occurs when a compound is non-superimposable on its mirror image. For an octahedral complex with six different ligands, it will always be optically active. So, there will be two optical isomers - one is the original molecule and the other is its mirror image.

So, for the given coordination compound Z, there are a total of 2 isomers.