SPECTROSCOPIC AND MAGNETIC STUDY OF THE (MG,M)(3)(ASO4)(2)CENTER-DOT-8H(2)O (M=NI2+,CO2+) ARSENATES

Compounds of general formula (Mg,M)(3)(AsO4)(2) . 8H(2)O (M = Ni2+), C o2+ have been synthesized and characterized, The crystal structure of the (Mg2.5Ni0.5)(AsO4)(2) . 8H(2)O compound has been refined using the Rietveld method. The final reliability factors are R(p) = 5.62, R(wp) = 7.06, and R(B) = 5.29. Crystallographic studies reveal that both th e ionic radius of the cations and the symmetry of the octahedral sites can play an important role in determining the cation ordering in thes e compounds. Diffuse reflectance spectra indicate a significant covale nce in the nickel and cobalt-oxygen bonds. The analysis of the magneti c measurements and the structural features shows a strong dimer ferrom agnetic interaction in the compounds.