Single-crystal and multi-frequency EPR studies on chemical analogues of Amavadin: V(IV)-doped Ca[Ti(hida)2]·6H2O, and Mo(V)-doped [PPh4][Nb(hida)2] and [NEt4][Ta(R,R-hidpa)2] [H3hida=2,2′-(hydroxyimino)diacetic acid, H3hidpa=2,2′-(hydroxyimino)dipropionic acid]