Li + (C 4 H 5 0 5 rC 4 H 6 0 5 , P2 U a = 5.269(3) Â, 6= 16.915(5) A, c = 6.403(3)Â, β = 94.05(2)°, Ζ = 2, D cxp = 1.588(6) g/cm 3 , D x = 1.598 g/ cm 3 . The Li + ion is found in a fivefold coordination surrounded by oxygen atoms in the form of a distorted pyramid with an almost rectangular base. The conformation of the malic acid moieties is anti. The crystal structure is characterized by endless chains of molecules connected threedimensionally by strong hydrogen bonds.

Large single crystals of optical quality and dimensions up to 20 χ 30 χ 50 mm have been grown from aqueous solutions. Complete dielectric, optical, piezoelectric, electro-optic, elastic and thermoelastic tensor properties were determined. All these properties exhibit a large anisotropy. The piezoelectric and electro-optic effects are only of the order of magnitude of those of α-quartz. The low value of the volume compressibility, as compared with Li 2 Ge0 3 , indicates the existence of monovalent HSe0 3 ions as postulated by .