Determination of the structural parameters of the crystalCdCl2by use of transition-metal-ion probes

Abstract

The bonding distance R and the trigonal distortion of complexes M${\mathrm{Cl}}_{6}^{4\mathrm{\ensuremath{-}}}$ at 77 K formed in ${\mathrm{CdCl}}_{2}$ crystals by substitution of ${\mathrm{Ni}}^{2+}$ and ${\mathrm{V}}^{2+}$ for ${\mathrm{Cd}}^{2+}$ have been determined from existing EPR and optical-transition data. The two different ion probes yield consistent results, which also agree with x-ray data for the position, but will be shown to be more precise by nearly an order of magnitude. This accuracy estimate depends on the validity of the theoretical calculations based on a point-charge-dipole model with a covalency correction. The case of ${\mathrm{Mn}}^{2+}$-ion probe in ${\mathrm{CdCl}}_{2}$ crystals is also discussed. In view of the fact that the theory is more complex for the $^{6}$S-state ion ${\mathrm{Mn}}^{2+}$ than for F-state ions and that a complete theoretical treatment of zero-field splittings for $^{6}$S-state ions is very difficult, it is concluded that for the determination of structural parameters of diamagnetic host from EPR spectra, the S-state-ion probe is not as effective as the F-state-ion probe.