RUBIDIUM TETRACHLOROCADMATE - X-RAY-DIFFRACTION MEASUREMENTS AND AN ELECTRONIC-STRUCTURE STUDY

The structure of Rb2CdCl4 single crystal at roam temperature has been determined from X-ray diffraction of the MoK alpha line (lambda = 0.71 07 Angstrom). After refinement through blocked least-squares methods, the reliability factor R in the final cycle is 3.07%. The following re sults have been obtained: tetragonal system, space group a = b = 5.195 (1) Angstrom, c = 16.130(1) Angstrom; F(000)= 380; Dm = 3.243 g/cm(3); Z = 2. The structure can be viewed as made of layers of CdCl6 octahed ra chains (Cd-Cl(1)= 2.597(1) Angstrom and Cd-Cl(2)= 2.572(1) Angstrom ) separated by double slabs of rubidium atoms perpendicular to the c d irection. First-principles density functional theory calculations have been carried out to determine the electronic density distribution. Th e calculated equilibrium structure is in satisfactory agreement with t he experimental data. Electronic density maps have been drawn from ab initio wavefunctions calculated both at the experimental and theoretic al equilibrium geometries. Analysis of the calculated atomic populatio ns confirms the highly ionic character of the electronic charge distri bution in the crystal. (C) 1998 Academic Press.