Electron paramagnetic resonance studies of single crystals of Mn  -doped (NH ) SO , Gd  -doped NH Pr(SO ) .4H O,VO  -doped M(NH ) (SO ) .6H O (M = Cd, Co, Fe, Mg, Zn) and Mg(ND ) (SO ) .6D O, and Cu  -doped MNa (SO ) .4H O (M = Co, Mg)