I suspect the issue is that $PATH is being expanded when you don't want it to be. The export command isn't treated any differently. Export expects the name of an environment variable to export, but you aren't giving it the name of the variable, you are giving it the variable reference itself, which gets expanded.
Think about this:
echo PATH
outputs
PATH
However, this
echo $PATH
outputs this:
{{/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin}:/Users/pavbond007/Documents/Mongo/mongodb-osx-x86_64-2.2.3/bin}:/Users/pavbond007/Documents/Mongo/mongodb-osx-x86_64-2.2.3/bin
Therefore, to export the PATH variable, try this instead (notice the lack of dollar sign):
export PATH
Also, I noticed your $PATH has a bunch of curly braces in it. Take those out. I'm pretty sure that is breaking things.
To do this in one line like you tried first, let's bring it all together:
export PATH=$PATH:~/mongo/bin