Effect of a First-Order Phase Transition at High Pressure on Ligand-Field Spectra

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Abstract
The effect of pressure to 140 kbar has been measured on the 10Dq peak in [Ni(NH3)6]X2, where X is Cl−, Br−, or I−. At about 70 kbar there is a first‐order phase transition which presumably rearranges the halide ions with respect to the Ni(NH3)6++ molecular ions. This rearrangement has a measurable effect on the ligand‐field energy 10Dq. For the chloride there is a decrease of about 100 cm−1, for the bromide a decrease of about 30 cm−1, while for the iodide there is an increase of about 80 cm−1. Measurements on the A2g(F)→T1g(F) transition in the chloride and bromide indicate that B decreases with increasing pressure in the low‐pressure phase, that there is little or no discontinuity in B at the transition, and that B is nearly independent of pressure in the high‐pressure phase.