Conversion of fluorides into chlorides, bromides or iodides

1542

Notes TABLE 2 . - - S T R U C T U R E TYPES OF COMPOUNDS

Ln

La

Pr

Nd

Sm

Eu

Gd

Tb

Dy

LiLnSiO4 AND LiLnGeO4 Y

rr, ns+(A) * 1"14 1"06 1'04 1"00 0"98 0"97 0"93 0"92 0"92 LiLnSiO4 h h h h h h h h o LiLnGeO4 h h t t t t t o o

Ho

Er

Tm

Yb

Lu

0"91 o o

0"89 o o

0'87 o o

0"86 o o

0"85 o o

* According to AHRENS. t, tetragonal; h, hexagonal; o, orthorhombic. The compounds LiLnSiO4 are either hexagonal or orthorhombic, depending on the ionic radius of Ln 8+. The orthorhombic compounds are isomorphous with monticellite, CaMgSiO~, which can be considered as an ordered olivine structure. The lattice parameters and X-ray diagram of the hexagonal compounds show some relationship to the hexagonal ct-K~SO~ structure, although the value of the a parameter in our case is C 3 times that of the ct-K~SO4 structure. In the series LiLnGeO~ three different structure types occur. For the larger Ln 3+ ions the hexagonal structure was found and for the smaller Ln a+ ions the monticellite structure. For the Ln s+ ions of medium size the compounds LiLnGeO4 have an X-ray pattern which could be indexed tetragonally (apart from small splittings of reflexions at high angles). This probably represents a new structure type.

Philips Research Laboratories N. V. Philips' Gloeilampenfabrieken Eindhoven-Netherlands

G. BI.ASSE J. DE VRIES

J. inorg, nucl. Chem., 1967, Vol. 29, pp. 1542 to 1544. Pergamon Press Ltd. Printed in Northern Ireland

Conversion of fluorides into chlorides, bromides or iodides (Received 13 December 1966) BECAUSE of the difficulty of transforming the lower halides into their higher homologues, some study and research was carried out on this type of reaction. Although this was undertaken for the solution of specific problems in the field of nuclear fuel reprocessing by non-aqueous methods, it is of general interest for the preparative chemistry of very pure compounds. For example, after the fluorination of uranium and plutonium there was no method available for transforming the fluorides directly into chlorides, bromides or iodides because the free energy of the reaction is too low. The same problem occurs in the electrolysis of uranium fluoride in molten lithium-potassium chlorides, where the fluoride content of the melt increases continuously and beyond a certain proportion becomes a nuisance in the operations. Among different reactions which may be considered the first consists of a double transformation of the type: X F + YC1 --~ XC1 + Y F (1) This reaction proceeds if the overall free energy of the reaction is negative, but leads to a mixtme of components which are hard to separate. This inconvenience may be avoided by using hydrogen halides as reagents; although these are volatile the free energy of the reaction is generally rather low. The transformation of fluorides by gaseous HCl has been described in the literature as an industrially exploitable reaction, m A third method, which is less powerful than the preceding one but interesting for selective reactions, utilizes carbon tetrahalides as halogenating agents, especially when oxides are present. m Conversion of alkali metal fluorides to chlorides U.S. patent No. 3,129,151, April 14, 1964.

Notes

1543

The new method described here is based on the reaction of silicon tetrahalides which are very powerful halogenating agents, reacting as follows :cs,s~ m

m

AX,,, + ~ SiY4 = AY,~ + ~- SiX~

(2)

where AX~ is the halide to be transformed and SiY4, the halogenating agent. Because of the great difference between the free energies of formation of SiF4 on the one hand and of SIC14, SiBr4 or SiI4 on the other, the reaction is of general use for transforming lower halides directly into higher ones. Table 1 summarizes the thermodynamic properties of the halides of hydrogen, carbon and silicon. TABLE I.--THERMODYNAMIC PROPERTIES (z,a) So

CF4 CC1, CBr, CI4 HF HC1 HBr HI SiF, SIC14 SiBr4 SiI4

-~xn;,8

-~o~,~

(cal/°C

(kcal/mole)

(kcal/mole)

per mole)

162.5 (g) 25.5 (g) --12 (g) -64.2 (g) 22.0 (g) 8.6 (g) --6.2 (g) 370.8 (g) 150.1 (g) 95.1 (l) 31-6 (s)

151-9 (g) 15.3 (g) --8'6 (g) -64-7 (g) 22.8 (g) 12.7 (g) --0.3 (g) 360.9 (g) 134.1 (g) 90.9 (l) 32.4 (s)

62.7 73.95 85.6 41.47 44-62 47.44 49.31 68-0 79.2 63 63

Some halogenation reactions which are difficult or impossible to perform by the other methods are given below as examples. A G~as (kcal/mole) UF4 + SiCI4 = UCI4 + SiF4 (3) --29.7 UF4 + SiI4 = UI4 + SiF4 (4) --53"4 UFe + 1.5 SiCI4 = UCle + 1.5 SiF4 (5) --96.3 PuFe + 1.5 SIC14 = PuCla + 1-5 SiF4 + 1-5 CI~ (6) --120 The transformation temperature of LiF into LiC1 with SiCI4 is ,'.- 250°C; with NaF it is necessary to heat to 400°C and with K F the reaction starts at ,~ 500°C. Reaction (3) starts at ,~ 400°C. ~4~These temperatures were determined by thermogravimetry. It may be calculated that the efficiency of the halogenating reagents increases in the order CX4 < HX < SiX4 where X represents the halogen. Based on this efficiency series, selective halogenations may be performed. An interesting feature is that these reagents may be applied to solids, liquids or gases because of their volatility, and the reactions may be carried out in either static or fluidized bedstSL The same t2J A. GLASSN~.R,The thermochemical properties of the oxides, fluorides and chlorides to 2500°K. A N L 5750. ~a~ W. J. COOPER and D. A. SCARPmLLO, Thermodynamic properties of metal bromides, iodides. SC-RR-64-67 (1964). c4~ PH. SPEECKAERT,G. DUMONTand A. VERHEYEN,Retraitement des combustibles irradi6s. Rapport trimestriel No. 22, pp. 8-11 E U R A E C 1601, E U R 2819 (1965). ~5~ PH. SPEECKAERT,G. Dtn~ONT, A. VERI-mWNand A. BLOK, Retraitement des combustibles irradi6s. Rapport trimestriel No. 24, pp. 6-7 (1966).

1544

Notes

reactions have been applied with good results in converting fluorides to chlorides in molten salts, tl,e~ Reaction in a homogeneous gaseous phase is also possible, but its utilization depends on the possibility of separating the gases at the outlet of the reactor. An important application of an homogeneous gas-phase reaction is the possibility of transforming UF6 and PuF6 directly to UCI6 and PuCI3 with SIC14 (reactions (5) and (6)). It is known that the highest chlorides of uranium and plutonium are UC16 and PuCl4-PuCla and that the vapour pressure difference between these species is very large. The ratio of the vapour pressures of UC16 and PuCI~ at 300°C is about 106 and is many orders of magnitude greater with PuCI~. Since the separation of uranium and plutonium as fluorides is difficult, this method may perhaps provide a successful alternative. Applied Radiochemistry Section PH. SPEECKAERT Centre d'Etude de l'Energie Nueldaire Mol Belgium is) PH. SPEECKAERT, G. DUMONTand A. VERHEYEN,Retraitement des combustibles irradi6s. Rapport trimestriel No. 25, pp. 30-32 (1966).

J. inorg, nucl. Chem., 1967. Vol. 29. pp. 1544 to 1546. Pergamon Press Ltd. Printed in Northern Ireland

The single crystal spectra of copper oxinate (Received 10 January 1967) INTRODUCTION THE INSOLUBILITYof the oxinates of the transition metal ions like copper(II) nickel(II) lead to the use of 8-hydroxy quinoline as an analytical reagent. Attempts have been made to associate the insolubility of the complexes with metal-metal bonding, although there is no definite evidence for it. Recently the absorption spectra of the copper and the nickel complexes of substituted 8-hydroxy quinoline in pyridine solution have been reported. ¢1) The analysis of the high energy region of the spectra shows that the bonding of the ligands are very much affected both by the substitutions in the rings and complex formation with the transition metal ions. The spectra have been studied in highly basic solvents like pyridine-where the metal ion has an octahedral disposition of the ligand atoms with two molecules of the solvent occupying the axial positions. The crystal structure of the copper oxinate (anhydrous) have been reported by KANAMARUet al. ~j It crystallizes in the monoclinic form with eight molecules per unit cell. A copper atom is surrounded by two nitrogen and two oxygen atoms in a square planar geometry. Weak dimeric unit of Cus (oxine)4 with a Cu-Cu distance of 3.54A has been postulated, although magnetic measurements down to liquid air temperature do not show any antiferromagnetism as in the case of basic copper acetate. In this paper we are reporting the single crystal absorption spectra of anhydrous copper oxinate. Single crystals of the compound were grown from the pyridine solution of the dehydrated complex by controlled evaporation at 40°C. Well developed hexagonal tabular faces (100) were selected for recording the spectra. The face is also the cleavage face and very thin section was cleaved off to record the spectra at the high energy region. The crystals show nice polarization when seen through polarized light---dark brown when seen parallel to the b-axis and light greenish yellow when the light is polarized pelpendicular to the b-axis. The crystals were mounted on thin quartz plate and a copper--constantan thermocouple is attached very close to the crystal to record the temperature. Low temperature spectra were recorded in a specially designed dewar cell with no liquid coolant in the optical path. The spectra were recorded on a Cary-14 recording Spectrophotometer. RESULT AND DISCUSSION The recorded spectra are shown in Figs. 1 and 2. The copper oxinate has an absorption band in the i.r. region which is not present in pyridine solution. It is a weak broad band and is not resolved even at 80°K. This is most likely the d--d transition s of the metal ion as in the case of other distorted (1) L. MORGANOand R. J. P. WILLIAMS,J. chem. Soc. A 73 (1966). t~) F. KANAMARtr,K. OGAWAand I. NATTA,Bull chem. Soc. Japan 36, 422 (1963).