Cobalt Centers in Strontium Tartrate Tetrahydrate
Considerable amount of work has been reported on divalent cobalt ion embedded in different crystalline matrices. For example, optical absorption of Co2 + ion surrounded by an octahedron of halogen ions has been analysed by FERGUSON et al. and an octahedron of water molecules by PAPPALARDO et al. and HOLMES, MCCLURE. The above type of studies on Co2+ ion in several oxides have also been reported. In the present work electronic absorption studies on Co2+ ions in strontium tatrate tetrahydrate (SrTr . 4 H 2 0 ) single crystals have been carried out before and after subjecting the crystals to 9-irradiation. Single crystals of SrTr . 4 H,O are orthorhombic with space group P2,2,2 (BOHANDY, MURPHY) with the following data: a = 9.48 A, b = 10.96 A and c = 9.46 ft and z = 4.
The cations Sr2 + exhibits eight fold co-ordination with co-ordination polyhedra of oxygen atoms forming a distorted dodecahedron. Preliminary ESR studies of the transition metal ions of the first series in SrTr ' 4 H 2 0 show results which are similar to those of CaTr . 4 H20.
In the latter case, the replacement of Ca2+ ion by a transition metal ion is ruled out and the ion was found to enter into a distorted octahedral interstitial site provided by six oxygen atoms.