[en] It was pointed out that the linear relation holds between transition point Tc and hydrogen bond distance R in the members of a number of the same type crystal groups that have one, two or three-dimensional hydrogen bond network. It was also shown that the linear relation holds between transition point Tc and the distance δ between proton sites. On the contrary in M₃H(XO₄)₂ type crystals, the hydrogen bond forms only a dimer by connecting two XO₄ and exists locally, but does not form hydrogen bond network. It was proposed to call this zero-dimensional hydrogen bond network. This matter system has the very contrasting, conspicuous isotopic effects of the shift and disappearance of the transition point. The expression of the isotopic effect of transition point is discussed. Hydrogen bond networks and their dimensions, the linear relation of Tc and R, and the cause of the disappearance of phase transition in M₃H(XO₄)₂ type crystals are reported. Phase transition disappears due to the low temperature shift of transition point. (K.I.)