How can I set cron to run certain commands every one and a half hours?

That’s not possible with a single expression in normal cron.

The best you could do without modifying the code is:

0 0,3,6,9,12,15,18,21 * * *  [cmd]
30 1,4,7,10,13,16,19,22 * * * [cmd]

These might be compressible, depending on the version of cron you have to:

0 */3 * * * [cmd]
30 1-23/3 * * * [cmd]