Experimental and theoretical investigations of the EFG parameters at the Br site in Cd(BrO<inf>3</inf>)<inf>2</inf>·2H<inf>2</inf>O

In Cd(BrO3)2·2H2O there are two chemically inequivalent sites of bromine in the unit cell which give rise to two nuclear quadrupole resonances for each isotope of bromine both at RT as well as at LNT. Single crystal Zeeman experiments carried out on the 79Br resonances at RT have revealed the presence of four physically inequivalent sites belonging to each crystallographic site of bromine and the EFG parameters at these sites have been obtained. The conventional point-charge model, when applied to this system for the evaluation of the field gradient at the Br sites, has yielded unsatisfactory results. In an attempt to include the effect of the covalent bonding in the bromate group, CNDO/2 MO calculations have been carried out on the two inequivalent bromate groups of the system and from the resulting population densities in the orbitals, intraionic EFG or qcov has been estimated. Later, interionic contribution qion, obtained from a point-charge approximation to the rest of the lattice has been added to q cov to obtain the total EFG. The results obtained from this model are in good agreement with the experimental values and it is found that intraionic EFG forms more than 95% of the total EFG at the Br site. © 1983 American Institute of Physics.