I have installed Marvin 5, but Marvin 4 opens up in IJC. How do I point IJC 2.2 to Marvin 5?
I am afraid it's not possible. IJC always contains own Marvin/JChem version co-bundled - you can see the used version number in release notes
for each IJC release.
We could not integrate Marvin 5 in IJC 2.2 because we were in late stabilization phase when Marvin 5 was finished. And IJC 2.2.1 was just a bug fixing release.
Upgrade to Marvin 5 is the most important feature in IJC 2.3 which is planned for April.
IJC 2.3 is released which now includes Marvin 5.0.3.