The Crystal Water Affecting the 2Eg→4A2g Relaxation in Tris(oxalato)chromate(III) Complexes

The measurements of absorption and luminescence spectra and luminescence decay are carried out on pure crystals of Na3[Cr(ox)3]·xH2O (ox2− = C2O42−) (x = 5 or 4) and Li3 [Cr(ox)3]·yH2O (y = 6 or 5). In sodium salt, dehydration of one crystal water (x = 4) causes the luminescence intensity to be about thirty times larger and the lifetime to be about thirty times longer than those of the most hydrated crystal (x = 5) while the opposite trend is obtained in lithium salt. However, in both salts, no change of the position of luminescence maximum is observed by the dehydration of one crystal water from the most hydrated crystals. Comparing these results with X-ray crystallographic analyses shows that a crystal water located near the oxalato-oxygen atom, which is coordinated to Cr3+ ion, affects the 2Eg→4A2g (all in Oh notation) relaxation of [Cr(ox)3]3− complexes in the pure crystal.