The method of preparing CsCoC1, single crystals is described. The absorption spectrum in the visible and infrared region and the pycnometric density of the sample have been measured. I n a previous paper (TRUTIA : Voda) the crystal growth of CsCoCl ,and the corresponding visible, low temperature spectrum were reported. Similar Similanly other compositions with Cs replaced by Rb, or K, also have been grown and their spectra recorded (TRUTIA, VODA, VASILE). I n these papers is shown how the tetrahedral symmetry, prefered by divalent cobalt a t low ratios of CoCl,/MCl (M = Cs, Rb, K) in a polycrystaline solid, passes to an octahedral one when the above mentioned ratio is increased. There are -as also shown there a band shift and structure differences between the octahedral spectra of Co2+ in CoC1, and in MCoC1, samples (the MCoC1, spectrum is always shifted towards the red compared t o the CoCl, one). These samples, however, were not proper for molar extinction coefficient measurements, nor for the determination of crystal field parameters (crystals were needle like and they could not be measured in the near infrared region).The purpose of this investigation was t o complete the previous papers with these data, as molar extinction coefficient, E, and the principal crystal field parameters D q and B values for CsCoCl,. The proper, large single crystals were used in this respect.1. The single crystal of CsCoC1, was prepared1) in the following manner: First, anhydrous cobalt(I1) chloride was prepared in a horizontal glass ampoule by passing a stream of phosgene over the dihydrate of cobalt(I1) chloride at 500 "C for a period of 2 hours. A slight stoichiometric surplus of anhydrous cobalt(I1) chloride was then mixed with cesium chloride ; the mixture was transfered into a quartz ampoule that was placed into a refinery furnace.
