From a temperature dependent ESR study of Mn²⁺ -doped crystals of M(BF₄)₂6H₂O, M = Zn, Co and Ni, new structural phase transitions have been detected and studied. First order structural phase transitions occur in Co(BF₄)₂6H₂O at T₁ ~281 K, T₂ ~189 K and T₃ ~ 172 K (during cooling), in Zn(BF₄)₂6H₂O at T₁ ~ 286 K and in Ni(BF₄)₂6H₂O at T₁ ~ 301 K. A continuous phase transition occurs in Co(BF₄)₂6H₂O at T_p ~ 257 K, in Zn(BF₄)₂6H₂O at Tp ~ 277 K and in Ni(BF₄)₂6H₂O at Tp ~ 294 K. The ESR spectral characteristics suggest similarities in the structures of these fluoroborate compounds in the phase above T₁with the room temperature structure of Mg(ClO₄)₂6H₂O. All these compounds are found to have a tendency to crystallise in a triply-twinned pseudo-hexagonal form, although the unit cell above T₁ is found to be orthorhombic. The structural changes related to the water octahedron around the metal at T₁ were found to be very small and basically the same for these three compounds. Although the unit cell structure of Fe(BF₄)₂6H₂O above the first order phase transition temperature T₁ was found to be similar to that of the other fluoroborate compounds, the structural changes occurring at T₁ appeared to be quite different. The low temperature thermal behaviour differs considerably in the Co, Fe and Zn compounds.