[rycharles]

What is the electron count for this transition metal compound?

1. Mo(CO)6

my attempt

CO 2e x 6 =   12e
Mo 6e x 1 =   6e
total         =   18e

2. Mo2(O2CCH3)4

my attempt

O2CCH3-    2e x 4  = 8e
Mo2+       4e x 2    = 8e
total                      = 16e

3. K4Mo2Cl8 (for this one, do I just ignore the K because its not really attached and analyze the compound Mo2Cl84-?)

Cl-  2e x 8   = 16e
Mo2- 4e x 2 = 8e
total            = 24e

[MrTeo]

1. Mo(CO)6

my attempt

CO 2e x 6 =   12e
Mo 6e x 1 =   6e
total         =   18e

Seems OK to me.

2. Mo2(O2CCH3)4

my attempt

O2CCH3-    2e x 4  = 8e
Mo2+       4e x 2    = 8e
total                      = 16e

What about the Mo-Mo bond?

3. K4Mo2Cl8 (for this one, do I just ignore the K because its not really attached and analyze the compound Mo2Cl84-?)

Right.

Cl-  2e x 8   = 16e
Mo2- 4e x 2 = 8e
total            = 24e

What about bridging Cl^-s? I think it's also better, both in this case and in the one before, to just count the electrons for one Mo (obviously the result is the same, but, especially when there are bridging ligands, working on the whole cluster at once can be quite confusing)

[rycharles]

For 2, did I not take the Mo-Mo bond into account by multiplying the number of Mo's by 2?  So each metal cation has a charge of +2 because they are d6 metals.

For 3, I don't think there are any Cl-'s bridging for this compound.  Only the Mo's are connected and each Mo has a square pyramidal structure with 4 Cls attached to it.

[MrTeo]

For 3, I don't think there are any Cl-'s bridging for this compound.  Only the Mo's are connected and each Mo has a square pyramidal structure with 4 Cls attached to it.

Ok. I actually didn't remember the structure of this compound so I took a guess. What about Mo-Mo (multiple) bond? If you count those electrons too you'll find 18e^- per Mo.

For 2, did I not take the Mo-Mo bond into account by multiplying the number of Mo's by 2?  So each metal cation has a charge of +2 because they are d6 metals.

Nope, you didn't. Each Mo shares a number of electrons equal to the order of the Mo-Mo bond, it's a covalent bond after all...
Moreover, did you take into account the presence of bridging acetate ligands?