AN INSIGHT INTO OPTICAL AND EPR PROPERTIES OF AGCL6(4-) AND AGF6(4-) COMPLEXES THROUGH MS-X-ALPHA AND SCCEH CALCULATIONS

MS-Xalpha and SCCEH calculations on the Ag2+ complexes AgF6(4-) and Ag C6(4-) (displaying an elongated D4h symmetry) have been carried out fo r a better understanding of their experimental optical and EPR propert ies. As salient features, the present work supports that the unpaired electron in AgCl6(4-) spends a little more time on ligands than on Ag2 +, in agreement with the previous analysis of EPR and optical data for KCl:Ag2+. Furthermore, the five experimental optical transitions obse rved in that case are reasonably assigned. The first transition (obser ved at 12,500 cm-1) is assigned to a jump involving the 5a1g orbital b uilt mainly (approximately 70%) from 3p orbitals of axial ligands, a f act that reflects the distinct level scheme for AgCl6(4-) when compare d to that for more ionic complexes. Calculations on AgF6(4-) and AgF4( 2-) performed as a function of the equatorial Ag2+ - F- distance led t o a reasonable understanding of experimental gyromagnetic and superhyp erfine tensors displayed by Ag2+ in fluorides. The different relative decrease undergone by g(parallel-to) - g0 (8%) and g(perpendicular-to) - g0 (28%) on passing from CsCdF3:Ag2+ to RbCdF3:Ag2+ is shown to be consistent with the formation of AgF6(4-) and AgF4(2-) complexes, resp ectively, related to the different substitutional position of Ag2+ in such lattices. The decrement of about 8.5% experienced by both g(paral lel-to) - g0 and g(perpendicular-to) -g0 values on going from CsCdF3:A g2+ to NaF:Ag2+ is pointed out to reflect the different electrostatic potential (exerted by the rest of the lattice upon the complex) seen b y AgF6(4-) embedded in NaCl or perovskite-type lattices. (C) 1994 John Wiley & Sons, Inc.