LINEAR RELATION BETWEEN TRANSITION-TEMPERATURE AND H-BOND DISTANCE INM3H(SEO4)2-TYPE CRYSTALS (M = K, RB, CS) WITH 0-DIMENSIONAL H-BOND NETWORK

A linear relation holds between the low-temperature transition point T c and H-bond distance R for M3H(SeO4)2-type crystals (M = K, Rb, Cs) w ith 0-dimensional H-bond netowrk: T(c) = 4154 (R - 4.495), where T(c) in K and R = O ... O in angstrom. Such a linear relation appears to be the general rule for crystals with 0- to 3-D H-bond networks. The mos t striking feature is that it gives an R value at T(c) = 0 K of 2.495 angstrom, which is longer than the values 2.40-2.45 angstrom in 1-D to 3-D H-bond networks and is incompatible with the knowledge so far obt ained. The puzzling nature of Rb3H(ScO4)2 with no phase transition, it s possible interpretations and the relation to the phase-transition mo del are discussed.