MODIFICATION OF CRYSTAL-STRUCTURE OF AMMONIUM ROCHELLE SALT [NANH4(-C(4)H(4)O(6.)4H(2)O] OWING TO THE REPLACEMENT OF NH4 IONS WITH K IONS())

The crystal structures of NaK1-x(NH4)(x)(+)-C4H4O6.4H(2)O (RS(1-x)ARS( x), x=0.90, 0.94 and 1.00) have been determined in the paraelectric ph ase (T=294K). The crystal data for ARS, orthorhombic, P2(1)2(1)2, R=0. 038, wR-0.032, no of reflections=3373, a-12.206(7) b=14,451(6), c=6.25 0(4)Angstrom, V=1102(1)Angstrom(3), D-x=1.573 g cm(-3), lambda(Mo-kapp a-alpha(1))=0.70926Angstrom, F(000)=552.00; for RS(0.06)ARS(0.94), ort horhombic, P2(1),2(1),2, R=0.0040, wR=0.030, no of reflections=2446, a =12.172(4), b=14.421(4), c=6.239(2)Angstrom, V=1095.2(6)Angstrom(3), Z =4, D-x=1.5292 g cm(-3), lambda(Mo-kappa-alpha(1))=0.70926Angstrom, F( 000)=553.92; for RS(0.10)ARS(0.090), orthorhombic, P2(1)2(1)2, R=0.036 , wR=0.0027, no of reflections=1898, a=12.165(9), b=14.420(7), c=6.239 (4)Angstrom, V=1094(1)Angstrom(3), Z=4, D-x=1.598 g cm(-3), lambda(Mo- kappa-alpha(1))=0.70926Angstrom, F(000)=555.20. In the crystals there are two crystallographically non equivalent cation sites occupied by K /NH4 ions. The accommodation ratios of sites (1)[(2A) by the Wyckoff n otation] and (2) [(2b)] are 0.94(1)and 0.92(1), respectively, in RS(0. 094)ARS(0.94), 0.90(1) and 0.93(1), respectively, in RS(0.10)ARS(0.90) . As x increases, the location site (2) displaces towards the origin. The hydrogen bonds around sites (1) and (2) are classified into two ty pes: one is that the distances become longer as x increases, due to th e differences in the ionic radii of K and NH4 ions, while the other is that the distances are equal. Comparing the crystal structure of ARS to that of RS, the following differences occur: the position of site ( 2), the interatomic distances between cations of sites (1) and (2) and oxygens, the form of the tartrate molecule and the position of some w ater molecules. These differences seem to be mainly caused by the repl acement of NH4 ions by K.