I was studying for GRE (I am taking it tomorrow) and I couldn't help finding out the point group when I saw this molecule. Too bad I'm obsessed with symmetry.
The article is here (DOI: 10.1039/C3MT00162H).
Since my drawing is not really good, I will try to explain where the "other" mirror plane is. If you imagine a plane that goes through the double bonded oxygen-Vanadium center and the equatorial OH2 molecule; the "right" and "left" side of the plane are the same.