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A LITERATURE SURVEY OF THE FLUORIDES AND OXYFLUORIDES OF MOLYBDENUM C. F. Weaver H. A. Friedman
NOTICE
This d ocument contains information of a preliminary nature and war prepared primarily for internal use at the Oak Ridge National Laborotory. It is subject to revision or correction and therefore does not represent a final report.
TM-
1976
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ORNL-TM-1976
Contract
No. W-7405-eng-26
REACTORCHEMISTRY DIVISION
A LITERATURE SURVEYOF THE FLUORIDES AND OXYFLUORIDES OF MOLYBDENUM C. F. Weaver and H. A. Friedman
OCTOBER
1967
OAK RTDGE NATIONAL LABORATORY Oak Ridge, Tennessee operated by UNION CARBIDE CORPORATION for the U.S. ATOMIC ENERGYCOMMISSION
2
A LITERATURE SURVEY OF THE FLUORIDES AND OXYFLUORIDES OF MOLYBDENUM C. F. Weaver and H. A. Friedman INTRODUCTION Molybdenum is one of the more important fission products with respect to the amount produced as well as its thermal neutron absorption cross section. Consequently the chemical behavior of molybdenum and its fluorides in molten salt reactor fuels which are in contact with graphite and Hastelloy b2,3 is of interest. A research program to determine the extent and rate of the pertinent reactions has recently been initiated. The necessary literature review of the fluorides and oxyfluorides of molybdenum is summarized in this report for the convenience of others. MoF, Reported methods for the synthesis of MoF, are: 1. MoBr, + 3HF -MoF, + 3HBr at 600째 in a Pt boat en4 closed in a Cu tube. 225OC 2. 2Mo + 6HF 2';1,hrs 2MoF, + 3H,? + MO -MoF, at 400째C in a Ni capsule. 6 3. MoF, + ?. The SbF, was carried in a 4. MoF, + SbF, -MoF, 6 stream of A at 150 to 2OOOC. The product produced by method (1) has different properties than that of methods (3) and (4). The authors of reference 6 stated that products similar to that obtained by method (1) were produced under hydrolyzing conditions. The properties of both materials are described below. Although it is possible for MoF, to exist in two crystalline forms, it is more likely that the product described in reference 4 is an oxyfluoride.
3 Properties reported for "MoF3" from method (1) are: non-hygroscopic, dark pink, shows no evidence of melting or subliming at 800°C in the absence of air, isi-'sos'tructural with ReQ, and.,TaB', (cubic., space group Pm3m, a = 3.8985 f 0.005) at <800°, has a distorted structure at >800°7 and is reduced 4 by H, to MO metal. The material produced by method (2) was found to be cubic by x-ray analysis5 and is probably the same as the product of method (1). Properties reported6 for MoF, from methods (3) and (4) are: variable color (ochre, light-green, gray, black, dark red, yellowish tan), stable to at least 900° in Ni under its own pressure, stable to 500° under vacuum, disproportionates above 600° to form MO metal and higher fluorides, density 4.64 f 0.07 g/cm3 (measured), 4.50 g/cm3 (x-ray) and VF, type structure (space group R~c) determined by x-ray and neutron diffraction. Other workers (ref. 8) have confirmed that MoF, has a bimolecular rhombohedral unit cell with the R~c space group. They have also shown that the compound is antiferromagnetic below 185OK. The trace of a neutron diffraction powder pattern taken at 4.2OK may be found in this reference. MoF, Reported methods for synthesis of MoF, are: + 3F6 -1-5'2Mo,FS + 12CO; Mo,Fg '.GOMOF4 + 1. AMOS MoF,.~ 2. Same as above except that the temperatures were -65O 10 and loo', respectively. 3. MOM + MoFb -MoF, + MoF, + CO; volatile prod10,ll ucts removed bv vacuum. 10,ll 4. MoF, >lSO MoF"6 -t MoF,. This compound has been described as light green, 9,11 9,10,11 non-volatile, and immediatelyhydrolyiable with HzQ..9
4 MO,
F,
.
An olive green solid of this composition has been re9,lO ported, but the authors of reference 9 suggested that It was preit was a mixture rather than a single compound. AMOS + 9F2 -65 to -7k02M~2F9 + pared by the reactions: 10051700 24C0 and disproportionates by the reaction: MO2 F, MoF, + MoF,. MoF, MoF, is a yellow hygroscopic substance which melts to 9,ll form a yellow viscous liquid. It fumes in air forming blue hydrolysis products, but is stable in air dried with and high Trouton constant of MoF, are p20, - The viscosity explained by assuming self ionization: 2MoF5 -MoF4 + + MoF;. 2 This compound has been synthesized by: 10051700 MoF 9110 1. MO2 F, 4 + MoF,. 2. 2MoF6 + PF, a*' 2MoF, + PF,. 12-14 "residue" diss11 MoF,.~~~~ 3. MO + F, -MoF6 + "residue", 10yy-frtz 4. MOM + MoF6 2z MoF, + MoF, + CO. 7-l 5. W(CO), + MoF6 -+MoF, + WF4 + CO? 6. Mo(CO), + F, -g'MoF,= + (?I 71 7. MoF6 + MO -MoF/~ 8. WF, + 2MoFb a@. 2MoF, + WF6. 13 MoF, disproportionates irreversibly (>150째) below its 10,ll boiling point to form MoF, and MoF6. Its vapor pressure in the range 70.0 to 160째 is given by log P = 8.58 - 2772/T.l" Table I provides a summary of the properties of MoF,. MoF, 12 dissolves in MoF6 to form a yellow solution. It is monoclinic (space group C2m) with a = 9.61 f 0.011, b = 14.22 f 11 0.021, c = 5.16 f O.Oli, and p = 94O 21' f 20'. An electron density projection on the 001 plane and a table of interatomic distances may also be found in reference 11. MoF, will reduce UF6 to UF, in excess UF6 and to UF, in excess MoF,. 14
-
5 W .
MMoFr The compounds MMoF615 (M = Na, K, Rb, Cs> were formed -60 O I, + 2MMoF6 and the impurities removed by: 2MoF6 + 2MI All of these compounds form by exposure to vacuum at 200째C. white crystals which are stable at 250째C, but attack glass KMoF6 has a magnetic above 250째C and turn blue in moist air. moment of 1.24 Bohr magnetons at 25OC, the low value being attributed to spin orbit coupling. The Na, Rb, and Cs compounds are cubic with a = 8.20, 5.11, and 5.29;, respectively. O 15 The K compound is tetragonal with a = 10.17 and c = 9.97A. O 11 The MO-F distance in NaMoF6 is 1.74 f 0.03A. The Na compound has been further studied (ref. 16) and found to be face centered cubic, space group Fm3m CO;, No. 255). All of the interatomic distances are listed in this report. K2MoOF, The compound KiMoOF, has been reported hydrolyzed pale green solid.
15 to be a readily
MoF6
I .
Molybdenum hexafluoride has been synthesized by: 1. F, + MO 60-300 MoF64910912917-21 in Pt boat in Ni with Nz. or Cu. F, diluted 22 2. MO + BrF, - MoF6 + ?. 3. MO + ClF, - MoFb + ? in Ni boat.20 20 4. MoCl, + HF - MoF6 + ?. The MoF6 is purified by trap to trap distillation over NaF . 12,17,23 The reactivity of MoF6 with respect to fluor13714 as' ination has been described . CrF, > UF6 > MoF~ > WF6. 18,24 and a colorless liquid. 19,20,24,25 It forms a white solid 24-27 with The colorless gas consists of octahedral molecules of 105Kcal/mole 13,28 d2sp3 hybrid bonds, has a bond strength 21 and has a second virial coefficient of -923 cm3/mole.
6 27 I 84$ The length of 1.83A.,' 29-311 13 1.8301MO-F32 bond has a reported 9 and a stretching force constant of 5.00, 1;,23 4.9972,35 4.9875,36 (:"l:'t37 4.73, 5.087,25 5.080,34 dynes/cm). The physical, structural, and thermal properties of MoF6 are summarized in Tables II-VII. Traces of the 19,25,27 19,24,27 25 and nuclear Raman, infrared, ultraviolet, 37 magnetic resonance spectra of MoF6 have been reported. The values of Cp", So, Ho - Hi, -(F" - Hi>/T for gaseous MoF6 in the ideal state have been calculated from the funda-
mental frequencies over the temperature range 50-1600'K and are tabulated in references 21, 24, 27, 31, and 38. The values of Cp determined calorimetrically for solid and liquid MoF6 from 50 to 298.5'K are tabulated in reference 39. The enthalpy and entropy of gaseous MoFb from 400 to 2000'K are tabulated4' and summarized as HT - H298.15 = 35.80T + 0.59 x 10-3TZ+ 6.97 x 105T-l - 13,064 (298-2000째K, 40 gas > and Cp = 35.80 + 1.18 x 10m3T - 6.97 x 105T-2.40 The functions Cp', So, Ho - Hg, -(F" - Hg)/T are also tabulated in reference 21 for solid 5-290.70째K, liquid 290.76 - 350째K, and gas 50 - 1000째K. The values for the solid and liquid are based on calorimetric data. Those for the gas are based on a combination of calorimetric and spectroscopic data. The System
MoF6-UF,
The system MoF6-UF6 has a eutectic 13.7'C, and incomplete solid solution. of the system may be found in reference
at 41
22 M/O UF6 and A phase diagram
41.
M,MoF, The reported. synthesize
family 22
of
compounds
M2MoF,
The authors of reference the sodium analog.
(M = K, 22 tried
Rb,
Cs) but
has
been
failed
to
-
I
7 MoOF, The compound MoOF, 4,10,33,42 tends to hydrolyze in air,33 but is stable in glass to at least 180째. Its vapor pressure is given by the following relations: 10 log P = 8.716 - 2671/T for liquid, 95-185OC log P = 9.21 2854/T for solid 40-950C1' Other physical and thermodynamic properties of this material are summarized in Table VIII. MoO,F, The compound MoO,F,~~'~~ sublimes with decomposition at W270째C42 and tends to hydrolyze in air. 33 Container
Materials
The fluorides of molybdenum react readily with moisture. Hence the systems in which they are handled must be scrupulously dried by outgasing, flaming, or baking. The following container materials have been used with molybdenum fluorides: Material Reference cu 12,18-21 Ni 13,18-21,23,41 Pt 18,23 Monel 21,23,41 Brass 41 Glass, Pyrex, quartz 12,13,17,18,20,24 Fluoethane 19 Kel-F tubes 13,14 Teflon 13,18,20,21,23,41 18 Fluorinated greases have been used, but packless all metal 12 values are to be preferred.The use of NaF as an HF getter will allow storage of MoF6 in glass at room temperature for 18,20 In general, glass and plastic many days without etching. type materials are useful to about 200째C above which the metals are necessary.
Physical
TABLE I Properties
of MoF5
M. P. B. P. T. P. AHvaporization
64째,apb 67c 213.6째,d 211C 67.0째, pressure 12,370 cal/moled
AS vaporization Vapor pressure Density Density
25.4 cal/mole/deg. -2mm (at 650Jc 3.44 (measured, 3.61 (x-raylc
very
lewd
d
solidjc
aR. D. Peacock, "lkro New Fluorides of Molybdenum," -Pm Proc. Chem. Sot., 59 (1957). %I. E. LaValle, R. M. and H. L. Yakel, Jr., Crystal Structure of J. Am. Chem. Sot. 82, --II
Steele, M. K. Wilkinson "The Preparation and Molybdenum (III) Fluoride," 2433-4 (1960).
'A. J. Edwards, R. D. Peacock, and R. W. H. Small, "The Preparation and Structure of Molybdenum Pentafluoride," J. Chem. Sot., 4486-91 (1962). --dGeorge H. Cady and George B. Hargreaves, "Vapor Pressures of Some Fluorides and Oxyfluorides of Molybdenum, Tungsten, Rhenium, and Osmium," J. @hem. Sot., 1568-74 (1961). --
9 TABLE II
v .
Thermal M. P. B. P. T. P.
and Structural
Properties of MoF6 17,a 17.4,b-d 17.5,e a9c9g 34.0~ch 35,
17.4*0.50Cf
17.5OC & 406.5mm,c'g 17.4 & 398.lmm -9.6,e'd -8f7 & 104.7mm, h Solid-Solid Transition -9.8kO.5 High Temperature Form bee a = 6.23ifri fi Low Temperature Form at -2O'C orthorhomic A a = 9.65h.02A b = 8.68*.03A c = 5.05*.02A aOtto Ruff and Fritz Eisner, "Uber die Darstellung und Eigenschaften von Fluoriden des Sechswertigen Molybdans," Berichte -SO, 2926-35 (1907). bT. A. O'Donnell, "The Preparation and Manipulation of Molybdenum Hexafluoride," J. Chem. Sot., 4681-2 (1956). 'N. S. Nikolaev and A. A. Opalovskii, "Solubility Isotherm at O" of the HF-MoF6-Hz0 System,",Russian 2. Inorg. Chem. 4, 532-6 (1959). dBernard Weinstock, "Some Properties of the Hexafluoride MoleRecord Chem. Progress 23, 23-50 (1962). cules," -eA. P. Brady, 0. E. Myers, and J. K. Clauss, "Thermodynamic Properties of High Fluorides. 1. The Heat Capacity, Entropy and Heats of Transition of Molybdenum Hexafluoride and Niobium Pentafluoride," J. Phys. Chem. 5-4, 588-91 (1959). --f L. E. Trevorrow, M. J. Steindler, D. V. Steidl, and J. T. Savage, "Laboratory Investigations in Support of Fluid-Bed Fluoride Volatility Processes. Part XIII. Condensed-Phase Equilibria in the System Molybdenum Hexafluoride -Uranium Hexafluoride," ANL-7240, August 1966. gVon Otto Ruff and Ernst Ascher, "Einige Physikalsiche KonZeitschrift fur anorganstanten von SiF4, WF6, and MOFg,(l ische und allgemeine Chemie. Band 196, 413-20 (1931). "The Vapor Pressures hGeorge H. Cady and George B. Hargreaves, of Some Heavy Transition-metal Hexafluorides," J. Chem. Sot., --1563-68 (1961). John G. Malm, Henry Selig, 'Darrell Osborne, Felix Schreiver, and Leo,1 Rochester, "Heat Capacity and Other Thermodynamic Properties of MoF6 Between 4O and 350째K," --J. Chem. Physics $2, 2802-9 (1966).
10
TABLE III Density
of
YoF6
8'C OOC
2.91 2.88
1ooc 278OK 237OK 17.5oc 19oc 270~ 34oc
c
17.4oc
d
d(Low Temp. Solid) for 77.16 to 237'K d(High Temp. Solid) d(Liquid) for 294.33 to 344.63'K
g/cc w
(measured)' 9,
(x-ray) 2.88 )) 2.88 f 0.04 (x-rayjb 3.27 * 0.03 w 2.551 g/cd 2.543 w 2.503 w 2.470 " 2.551 " -3.619 - 0.00 130T (g/cm')b - 3.464 - 0.0021OT (g/cm') b -3.733 - 0.00404T (g/cm')b
aL. E. Trevorrow, !I¶. J. Steindler, D. V. Steidl, and J. T. Savage, "Laboratory Investigations in Support of Fluid-Bed Fluoride Volatility Condensed-Phase Equilibria in the System MolyProcesses. Part XIII. bdenum Hexafluoride and Uranium Hexafluoride," ANL-7240, August 1966. % arrell Gsborne, Felix Schreiver, John G. Maim, Henry Selig Rochester "Heat Capacity and Other Thermodynamic Properties Between qd and 350°K," 2. . Physics 41, 2802-9 (1966). 'Van
Otto Ruff and Ernst Ascher, WF6, and YoF6,” Zeitschrift Band 196, 413-20 (1931). SiFI,
"Einige Physikalische fur anorganische
dN. S. Nikolaev and A. A. Opalovskii, "Solubility HF-MoF6-Hz0 System," Russian 2. Inorg. x. 4,
und
and Leon of IdoF
Konstanten allgemeine
Isotherm at 532-6 (1959).
von Chemie.
O" of
the
.
11 TABLE IV Vapor Pressures of MoF6 Solid
log p = -1g;3*1
+ 8.880a
Liquid
log p = -13T4.9
Liquid
log p = -14G9.9
f 7.407a + 7.766 b
Solid
17.4 to 34OC log P = -1722,9 T -8.7
Solid
to 17.4'C log P = -2166.5 T
+ 8.533 b + 10.216
b
-60 to -8.7'C Liquid
1% 10Pmm = -2047.15/TC -4.28004 loglOT
+ 20.19354 KonaVon Otto Ruff and Ernst Ascher, "Einige Physikalische fur anorganstanten von SiF,, WFb, and MoFC," Zeitschrift ische und allgemeine Chemie, Band 196, 413-20 (1931). bGeorge H. Cady and George B. Hargreaves, "The Vapor Pressures of Some Heavy Transition-metal Hexafluorides," J. Chem. Sot. --1563-68 (1961). 'Darrell W. Osborne, Felix Schreiver, John G. Maim, Henry "Heat Capacity and Other ThermoSelig, and Leon Rochester, dynamic Properties of MoFb Between 4O and 350째K," J-e Chem. Phys. 44, 2802-9 (1966). --
12
Thermodynamic %
AH(b8.7OC) AIYI~(<-~.~~C)
(AHvap 18 mV
rnv A?Iv(298.150K) mf mf AHf(290.7'K) % mt AHt(263.48."K) AsV
ASv(298.150K) asf mf
-.c
TABLE V Properties of MoF6 For Change of Statea 8.30 K cal/moleb C 1, 7.850 C 9.810 d t, 11.1485 b ,, 6.36 C 6.940 6.630 f 0.025 ,, d 1.059 f 0.010 ,t e 0.920 ,, C 1.0342 k 0,001 7, d 1.957 f 0.010 ,? e 1.960 11 C 1.9333 f 0.002 11 d
-
LI
0
lf
22.5 22.24 3.15 3.65 3.557 7.40 7.72
cal/deg/molec f
0.08
* 0.10
I!
d
,!
C
I,
,,
f d
9,
C
,1
f
a
s = sublimation v = vaporization f = fusion t = solid state transition bVon Otto Ruff and Ernst Ascher, "Einige Physikalische Konstanten von SiF,, WF,, and MoFg," Zeitschrift fur anorganische und allgemeine Chemie. Band 196, 413-20 (1931). 'George H. Cady and George B. Hargreaves "The Vapor Pressures of Some Heavy Transition-metal Hexafluoiides," J. Chem. Sot., --1563-68 (1961). dDarrell. Osborne, Felix Scbreiver, John G. Malm, Henry Selig, and Leon Rochester, "Heat Capacity and Other Themodynamic Properties of MoF6 Between 4O and 350째K," J. Chem. Phys. 44, --2802-9 (1966). eA. P. Brady, 0. E. Myers and J. K. Clauss, "Thermodynamic Properties of Higher Fluorides. 1. The Heat Capacity, Entropy, and Heats of Transition of Molybdenum Hexafluoride, and Niobium Pentafluoride," J. Phys. Chem. 64, 588-91 (1959). ----f Bernard Weinstock, "Some Properties of the Hexafluoride Molecules," Record Chem. Progress 22, 23-50 (1962).
*
13
TABLE VI Thermodynamic
Properties
Formation AH0 AH AH AH0 AEO AF” AF AF” fs” As0
(25'C, (25'C, (25'C, (25'C, (25OC, (25'C, (25'C, (25'C, (25'C, (25'C,
*At
vapor
gas) gas* 1 liq.) gas 1 gas) gas 1 liq. 1 gas 1 gas 1 gas 1 pressure
-372.3 -382 -388.6 -370.2 -371.1 -350.8 -361.2 -351.9 - 72.13 - 68.41
of MoF6.
Values. f 0.2
f 0.23 f 0.2 f 0.2
K cal/molea b 0 b II Tl fl
1, l?
f 0.23
?1
C
a a b C
cal/deg/molea f 0.19
tt
C
of liquid.
aJack L. Settle, Harold M. Feder and Ward N. Hubbard, "Fluorine Bomb Calorimetry. II. The Heat of Formation of Molybdenum Hexafluoride," J. Phys. Chem. 55, 1337-40 (1961). --b
0. E. Myers and A. P. Brady, "Thermodynamic Properties of Higher Fluorides. 11. The Heats of Solution and of Formation of Molybdenum Hexafluoride, Tungsten Hexafluoride and Niobium Pentafluoride," J. Phys. Chem. fiip 591-4 (1960). W-P
'Darrell Osborne, Felix Schreiver, John G. Malm, Henry Selig, and Leon Rochester, "Heat Capacity and Other Themodynamic Properties of MoF6 Between 4' and 350°K," --J. Chem. Physics 44, 2802-9 (1966).
14
Normal Ref. Vl v2 v3 v4 “5
“6
a? 741 643 741 262 312 122* *Calculated
TABLE VII Frequencies (cm-')
b 736
c,d 741
e,f 736
641 319 226* 619* 328*
645 741 260 322 234* TThese tent
641 742 269*
of
MoF6 g 736 641 742
h,j 741 643 741
k 738.5 643 741.5
269
264 306
264.5 320.5 237 consis-
319 319 240* 240 frequencies are with calorimetric
190 the most values.
aDarrell Osborne, Felix Schreiver, John G. Malm, Henry Selig, and Leon Rochester, "Heat Capacity and Other Themodynamic Properties of MoFb Between 4O and 350°K," --J. Chem. Physics 2802-9 (1966). 44, -b K. N.Tanner and A.B.F. Duncan, "Raman Effect and Ultraviolet Spectra of Molybdenum and Tungsten Hexafluorides," --J. Am. Chem. -Sot. -73, 1164-7 (1951). 'T. G. Burke, D. F. Smith, and A. H. Nielsen, "The Molecular Structure of MoF,, WF6, and UF6 from Infrared and Raman Spectra," J. Chem. Phys. 20, 447-54 (1952). ----d K. Venkateswarln and S. Sundaram, "Evaluation of Force Constants: Molecules of the Type XY6," --Z. Phys. Chem. (New Series) -9, 174-9 (1956). eJ. Gaunt, "The Infra-red Spectra and Molecular Structure of Some Group 6 Hexafluorides," Trans. Faraday Sot. 49, 1122-31 -(1953). f S. Sundaram, "Mean Amplitudes of Thermal Vibrations and Thermodynamic Properties of Metal Hexafluorides," Z. -- Phys. Chem. (New Series) 22, 225-32 (1962). 'G. Nagarajan, "Mean Amplitudes of Thermal Motion and Shrinkages of Chemical Bonds: Octahedral Hexafluorides," Indian J. ~-_-Pure Appl. Phys. 4, 237-43 (1966). h---Howard H. Claasen, Henry Selig, and John G. Malm, "Vibrational Spectra of MoF6 and TcF6," J. Chem. 36, 2888-90 (1962). --Phys. LJG. Nagarajan, "Potential Constants for the Hexafluorides of Molybdenum and Rhenium," Aust.' J. Chem. 16, 906-7 (1963). ----k C.W.F.T. Pistorius, "Potential Field and Force Constants of Octahedral Molecules," J. Chem. Phys. 29, 1328-32 (1958). ---we
15
TABLE VIII Physical
and Thermodynamic
M. P. B. P. T. P. Color AH fusion M fusion AI-I vaporization m sublimation AS vaporization
Properties
of MoOF,
97 oa,b 186.0째yc 180a'b'd 97.2' and 28.8mmc
WhiteC 1020 cal/molec 2.768 cal/mole/degc 12,090 eal/mole" 13,100 cal/molec 26.3 cal/mole/degc
aOtto Ruff and Fritz Eisner, "Uber die Darstellung und Eigenschaften von Fluoriden des Sechswertigen Molybdans," Berichte 42, 2926-35J(1907). bJ. Gaunt, "The Force constants and Bond Lengths of Some Inorganic Hexafluorides," Trans. Faraday Sot. 50, 546-51 (1954). 'George H. Cady and George B. Hargreavest "Vapor Pressures of Some Fluorides and Oxyfluorides of Molybdenum, Tungsten, Chem. Sot., 1568-74 (1961). Rhenium, and Osmium," 2. -dA. J. Edwards, R. D. Peacock, and R. W. H. Small, "The Preparation and Structure of Molybdenum Pentafluoride," J. Chem. Sot., 4486-91 (1962). a--
16 Y
References
t
1.
W. R. Grimes, "Chemical Research and Development for Molten-Salt Breeder Reactors," ORNL-TM-1853, June 6, 1967, pp. 61-81.
2.
S. S. Kirslis, F. F. Blankenship, and C. F. Baes, Jr., Reactor Chemistry Division Annual Progress Report, January 31, 1967, ORNL-4076, pp. 48-53.
3.
S. S. Kirslis and F. F. Blankenship, MSR Program Semiannual Progress Report, February 28, 1967, ORNL-4119, pp. 124-143.
4.
H. J. Emeleus and V. Gutmann, "Studies on the Fluorides of Molybdenum and Vanadium," --J. Chem. Sot., 2979-82 (1949).
5.
E. L. Muetterties and J. E. Castle, "Reactions of Hydrogen Fluoride with Metals and Metalloids," J. Inorg. and Nucl. -Chem. -18, 148-53 (1961). D. E. LaValle, R. M. Steele, M. K. Wilkinson and H. L. Yakel, Jr., "The Preparation and Crystal Structure of Molybdenum (III) Fluoride," J. Am. Chem. Sot. 82, 2433- -a 4 (1960).
6.
7.
V. Gutmann and K. H. Jack, "The Crystal Structures of Molybdenum Trifluoride, MoF,, and Tantalum Trifluoride, TaF, ,I' Acta Cryst. 4, 244-46 (1951).
8.
M. K. Wilkinson, E. 0. Wollan, H. R. Child, and J. W. Cable, "Neutron Diffraction Investigation of Magnetic Ordering in the Trifluorides of 4-d-transition Elements," Phys. Rev. 121, 74-7 (1961). Be-
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