Chetal, A R

Mande, Chintamani

English

IACS Institutional Repository

COBALT K X-RAY ABSORPTION SPECTRUM IN PINK ANP BLUE SOLUTIONS OF COBALT (II) CHLORIPEC H IN TA M A N I M AN DE A. R . CH ETALDepabtmentt op Physics, UirivtosiTY op Poona, Poona-7.{Received September 23, 1963; ^Mcmdmitted June 1 2 , 1964).Van Nordstrand (1960a, b) has recei^ly reported a large number of K  ab­sorption curves of transition metal ionsdn different types of compounds. He classifies these curves in four categories (see Sinha and Mande, 1963 for details). O f these, the type TV curves, that is the curves for the transition metal ions with tetrahedral surroundings, alone show the splitting of the principal absorption edge. Sinha and Mande (1963) have explained this splitting of the absorption (li.seontinuity on the basis of the ligand field theory. Tt appears, that the tetra- hedrally .surrounded metal ion gives a very characteristic A-ray absorption spec­trum . In this note we report the shape of the K  X -ray absorption disconti­nuity of cobalt in pink and blue solutions of cobalt chloride.A Cauchois tyfie bent crystal X -ray spectrograph of diameter 40 ems, designed and constructed in our workshop, was used in this investigation. A  well tried crystal o f mica was used as analyser. The spectra were photographed using the (100) and (2 0 l) reflections of mica. A  Philips sealed X -ray tube with tungsten target w^ as imiployed. It was operated at 20K V , the current ranging from 20ma to 30 m a. Exposure times varied from 12 to 30 hours on Agfa ultraviolet plates. Microphotometcr records o f the plates were obtained with magnification 50 on a Moll miorophotometer. The absorption cell containing the solution of cobalt chloride w'as placed in front of the X -ray tube window and w'as supported by means of two screws provided on the shield of the X -ray tube. The proper thick­ness of the absorbing solution was attained by placing the solution between two very thin films o f celluloid separated by a stainless steel sheet of requisite thiekness. Deep blue solutions were obtained by adding excess of concentrated HCl to the pink solutions.The forms o f Co K  absorption edge in pink and blue solutions of CoCl* res­pectively are shown in figures 1 and 2. These forms have been obtained from  several microphotometer records taken in turn from several plates obtained imder varying conditions of exposure. It is seen that these curves resemble very well w ith typo I  and type IV  spectra respectively obtained by Van Nordstrand. However, it should be noted that the curves given by Van Nordstrand are abaorp- tion coefficient versus energy curves, where as our curves show the variation of transm itted intensity with energy. It will be seen that Fig. 1 shows a single K19433434 Letter to the Editordiscontinuity wliile Fig. 2 shows the splitting of the principal absorption edge into two suc(^ c‘ssivc components and ivg. Both discontinuities sliow secondary fine stru(?ture near tjio absorption edge on the high energy side. However, for the blue solution, the curve somewhat flattens after the maxiniuni of the secondary structure.,s . s.Fig. I Fig. 2Figures 1 and 2 sliow the form of th(^  Co K aJ)sorptioii edge in pink and blue HoliitionsrespcH-tively of oabaltcldorido. The markings S. S. stand for st'condury slrueture.The K  absorption curves for ti)e pink and l)lue solutions of cobalt chloride obtained in this investigation are (*haracteristic of the transition metal ion asso­ciated with an octahedral co-ordination iii tin- common salts and the ion asso­ciated with a tetrahedral (configuration respe(;tjvely. Hence avcj comdude that in the pink solution the Co^  ^  ^ ion is o ‘tahedrally surrounded and in the blue solution the coordination is a tetrahedral one. In the geTu*ral interpretation given by Sinlia and Mandc, tlie minima at the markings V// and 'b' in Fig. 2 represent tlio X-ray absorption transitions U"—► 4/> and p limit. The empty 4/) orbital (jf the Co'  ^+ ion is localised only in the tetrah(.Tlral configuration, thus making possible the 1.V—>4p transition.TheSi^ results also establish  tlia t a lth o u gh  in  th e solu tion  states th e  la ttice  structure breaks dow n, th e in dividu al octahedral a n d  tetrah edral u n its around  th e cobalt ion retain their id e n tity . T h is  w ork th u s su p p orts th e . assu m p tion s  m ad e b y  M ookherji (1962) a b o u t th e  n atu re o f  th e  crystal fields in his recent  m agn etic  studies o f  these solutions.A C K N O W L E D G E M E N TO ur th an k s are due to  th e Council o f  Scientific and  In d u stria l R esearch , N e w  D elh i for sanctioning a research sch em e under w hich th is  w ork h as been don e.K E F E H E N C E SSinha K. P. aiuj Mande, C., 1963, Jnd. J. Phys., 257.Van Nordstrand, R. A., 1960, Conf. Non-crystallmo solids, John Wiley and Sons, New York.Van Nordstrand, II. A., 1960, Advances in Catalysis, Vol. 12, Acadomio Press, New York.Mookherji, T., 1962, Ind. J. Phys,, S6, 216.

Cobalt K X-Ray Absorption Spectrum in Pink and Blue Solutions of Cobalt (II) Chloride

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Cobalt K X-Ray Absorption Spectrum in Pink and Blue Solutions of Cobalt (II) Chloride

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