Transition Metal Hydrides - American Chemical Society

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 17, 2017 | http://pubs.acs.org Publication Date: June 1, 1978 | doi: 10.1021/ba-1978-0167.ch025

25 Results of Reactions Designed to Produce Ternary Hydrides of Some Rarer Platinum Metals with Europium or Ytterbium RALPH O. MOYER, JR., ROBERT LINDSAY, and DAVID N. MARKS Trinity College, Hartford, CT 06106

Bimetallic ternary hydrides in which at least one of the metal constituents is an alkali or an alkaline earth element and the second a transition element are reviewed first. The results of the preparation, structure, and properties of materials formed by reactions between EuH or YbH and ruthenium or iridium are described and interpreted. Eu RuH or Yb RuH can be formed by reacting EuH or YbH with ruthenium at 800°C in a hydrogen atmosphere. These ternary hydrides are isostructural with their alkaline earth-ruthenium analogs Sr RuH and Ca RuH , with the metal atoms arranged in a fluorite-type lattice. The magnetic susceptibilities are consistent with +2 oxidation states for europium in Eu RuH and for ytterbium in Yb RuH . The electrical conductivities of Eu RuH and Yb RuH6 show a temperature dependence typical of semiconductors. Ir data for Eu RuH and Yb RuH suggest absorption bands which could be attributed to ruthenium-hydrogen stretching and bending modes. Recent work concerning the preparation of the hydride systems europium-iridium-hydrogenand ytterbium-iridium-hydrogen are discussed. 2

2

2

2

2

6

2

6

2

2

6

2

6

6

2

2

6

6

2

2

6

2

6

P

resently, there is considerable interest i n using hydrogen as a fuel and i n using some metal hydrides as convenient, safe, a n d economical storage devices. In v i e w of the present concern for alternative energy supplies, these notions, a l though not exactly new, are nonetheless more appealing than when first proposed. G . F . Jaubert (I ) obtained a F r e n c h patent i n 1902 for the application of metal hydrides, and particularly calcium hydride, for the production of hydrogen. F i v e years later he received a British patent describing a n apparatus m o u n t e d o n a 0-8412-0390-3/78/33-167-366/$05.00/0 © American Chemical Society Bau; Transition Metal Hydrides Advances in Chemistry; American Chemical Society: Washington, DC, 1978.

25.

MOYER E T AL.

Ternary Hydrides of Some Rarer Pt Metals

367

carriage for an almost-continuous production of hydrogen f r o m calcium hydride (2, 3). T h e binary hydride was considered portable hydrogen for filling dirigible hulls.

B i m e t a l l i c h y d r i d e systems, i.e., ternary hydrides, of the general stoichi-

ometry Μ M Ή , where M ' is a d-block transition element and M is a rare earth, Χ

a d-block transition element, or an actinide element, have been studied exten sively.

These systems, w i t h the exception of those where M is e u r o p i u m or y t

t e r b i u m , w i l l not be discussed.

Recent reports b y H . W . N e w k i r k (4) and V a n

M a i (5) give reviews of these ternary hydrides along w i t h summaries of their


properties.

In addition, the large class of complex metal ternary hydrides of the

representative elements, such as L i A l H

4

a n d N a B H , some of w h i c h are used 4

extensively as r e d u c i n g agents, w i l l not be considered. T h i s chapter commences w i t h a review of a l i m i t e d n u m b e r of ternary h y dride systems that have two common features.

First, at least one of the two metal

constituents is an alkali or alkaline earth element w h i c h independently forms a b i n a r y h y d r i d e w i t h a metal hydrogen bond that is characterized as saline or ionic.

T h e second metal, for the most part, is near the end of the d-electron series

and w i t h the exception of p a l l a d i u m , is not k n o w n to f o r m b i n a r y hydrides that are stable at room temperature.

This review stems from our o w n more specific

interest i n preparing and characterizing ternary hydrides where one of the metals is europium or ytterbium and the other is a rarer platinum metal. T h e similarity between the crystal chemistry of these di-valent rare earths and C a

and S r

2 +

2 +

is w e l l k n o w n so that i n our systems, e u r o p i u m a n d y t t e r b i u m i n their di-valent oxidation states are v i e w e d as pseudoalkaline earth elements.

Li-M-H

Systems Where M = Eu, Sr, or Ba

Messer and his co-workers (6, 7) reported the formation of L i E u H , L i S r H 3 , and L i B a H b y heating a b i n a r y m i x t u r e of the respective elements i n 1 a t m H at 7 0 0 ° - 7 5 0 ° C for 2 0 - 3 0 m i n and then at 5 0 0 ° - 6 0 0 ° C for 2 - 3 hr before cooling. X - r a y powder diffraction patterns were indexed on the basis of a p r i m i t i v e cubic cell w i t h α = 3.796Å for L i E u H , α = 3.833Å for L i S r H , and α = 4.023Å for L i B a H . E a c h ternary hydride adopted the perovskite structure w i t h ρ = 3.378 g / c m for L i E u H , ρ = 2.877 g / c m for L i S r H , a n d ρ = 3.756 g / c m for LiBaH . 3

3

2

3

3

3

3

3

3

3

3

3

G r e e d a n (8) reported the preparation of L i E u H a n d L i S r H b y heating the respective b i n a r y hydrides at 700° C for V2 hr i n approximately 1 a t m H a c c o r d i n g to the f o l l o w i n g equation, where M = Sr or E u : 3

L i H + M H --> L i M H 2

3

3

H e also reported the preparation of large single crystals (13 m m i n diameter and 13-25 m m i n length) of L i E u H a n d L i S r H b y reacting the respective b i n a r y hydrides a n d g r o w i n g the crystals f r o m the melt b y a m o d i f i e d B r i d g e m a n Stockbarger technique. Single crystals of L i S r H were orange b r o w n ; those of 3

3

3

Bau; Transition Metal Hydrides Advances in Chemistry; American Chemical Society: Washington, DC, 1978.

2

368

TRANSITION M E T A L HYDRIDES

L i E u H were deep red. R o o m temperature electrical resistivities for L i E u H and L i S r H were approximately 1 0 o h m - c m , showing little change after a n nealing. 3

3

7

3

Potassium -Magnesium -Hydrogen System Ashby a n d his group (9) reported the formation of K M g H by the h y d r o genolysis of K M g ( s e c - C H ) H i n benzene according to the f o l l o w i n g equa tion: 3


4

9

2

KMg(sec-C H ) H + 2 H — K M g H 4

9

2

2

+ 2C H

3

4

1 0

A 0 . 5 M benzene solution of K M g ( s e c - C H ) H was hydrogenated at 3000 psi of hydrogen at 2 5 ° C for 4 hr. Because K M g ( s e c - C H ) H is soluble i n benzene, the technique avoided any necessity for hydrogenolysis i n more basic solvents such as ether, w h i c h might have competed with the hydride ion for a coordinating position on the magnesium. 4

9

2

4

9

2

K M g H was a yellow solid that reacted violently i n air. L i k e the l i t h i u m alkaline earth hydrides, K M g H possessed the perovskite structure a n d was isostructural w i t h K M g F . T w o broad absorption bands were observed for K M g H at 1150 c m " a n d 680 c m i n the ir spectrum. Because similar positions were observed for M g H , it was concluded that equivalent environments, w i t h respect to hydrogen, existed between six-coordinate magnesium i n the rutile M g H and the six-coordinate magnesium i n the perovskite K M g H . 3

3

3

1

3

- 1

2

2

3

Li-M-H

Systems Where M = Group VIIIB Metal

T w o ternary hydrides of the l i t h i u m - r h o d i u m - h y d r o g e n system, L i R h H and L i R h H , are k n o w n . J . D . F a r r (10) reported the formation of L i R h H by reacting freshly ground L i H and r h o d i u m at 600° C i n an argon atmosphere. L i R h H also was f o r m e d by heating L i R h H to 400° C i n a v a c u u m according to the f o l l o w i n g equation: 4

4

5

4

4

L i R h H --> L i R h H 4

5

4

4

4

4

4

5

4

+ V H 2

2

L i R h H was prepared by heating l i t h i u m a n d r h o d i u m or L i H a n d r h o d i u m i n hydrogen at 600° C a n d slowly cooled at 440° C i n a period of 1 hr w h i l e maintaining a hydrogen atmosphere of approximately 550 Torr. L i R h H and L i R h H 5 were reactive to water and alcohol, resulting i n hydrogen evolution and reformation of r h o d i u m . 4

5

4

4

4

Single crystal x-ray diffraction techniques were used to elucidate the structures of L i R h H a n d L i R h H (11). T h e unit cell of L i R h H was found to be tetragonal w i t h α = 6.338 A a n d c = 4.113 A, w i t h a probable space group of I4/m. T h e density was 2.707 g / c m , consistent w i t h two f o r m u l a units per 4

4

4

5

4

4

3


25.

unit cell.

Li RhH 4

369


MOYER E T AL.

5

was orthorhombic w i t h a = 3.880 A, b = 9.020 A, a n d c =

8.895 A; the space group was Cmcm.

T h e n u m b e r of formula units per unit cell

was four, g i v i n g a calculated density of 2.895 g / c m . 3

T h e magnetic susceptibility of L i R h H and L i R h H was measured at 51°, 75°, a n d 297° Κ i n a field of 4-10 k G ( I I ) . T h e molar susceptibility for L i R h H was 1.2 X 1 0 cgs and for L l j R h H s was 2.1 Χ 1 0 " cgs; both compounds showed temperature independent paramagnetic behavior. Room temperature electrical resistivities were 0.5 o h m - c m for L i R h H a n d 1.5 o h m - c m for L i R h H s ( I I ) . 4

4

4

5

4

6

4

6

4

4

4


Graefe a n d Robeson (12) presented evidence for the preparation of i m p u r e L i 3 l r H , l i t h i u m p a l l a d i u m h y d r i d e , and l i t h i u m p l a t i n u m h y d r i d e . 6

Li3lrH

6

was f o r m e d b y reacting L i H a n d i r i d i u m at 500 T o r r of H for 8 hr at 539°C. 2

L i 3 I r H , a light y e l l o w solid, reacted readily w i t h the atmosphere. 6

Potassium-Rhenium-Hydrogen Systems

and

Potassium-Technetium-Hydrogen

O n e of the most interesting accounts i n ternary hydride chemistry surrounds K R e H , potassium nonahydridorhenate(VII), f o r m e d b y the reduction of po tassium perrhenate w i t h potassium or l i t h i u m . P r i o r to 1960 the product was believed to be potassium rhenide. Floss a n d Grosse i n 1960 (13) suggested that the product of the reduction of perrhenate w i t h potassium i n aqueous e t h y l e n e d i a m i n e was a complex ternary h y d r i d e of r h e n i u m w i t h the f o r m u l a K ( R e H ) - 2 - 4 H 0 . A t about the same time, G i n s b e r g a n d co-workers (14) i n dependently announced i n a note that the product prepared i n a fashion similar to that reported b y Floss and Grosse was a h y d r i d e w i t h r h e n i u m i n a positive oxidation state. L a t e r G i n s b e r g et a l . (15) assigned the f o r m u l a K R e H to po tassium r h e n i u m h y d r i d e . It was not u n t i l 1964 that the structure of potassium r h e n i u m h y d r i d e was resolved unequivocally by neutron diffraction analysis and the composition was shown to be K R e H (16). O n the basis of single crystal x-ray diffraction, K R e H was hexagonal w i t h unit cell dimensions of α = 9.607 Λ and c = 5.508 A a n d three f o r m u l a weights per unit c e l l (17). T h e probable space g r o u p was D - P 6 2 m . T h e neutron diffraction studies supported a nine-coor dinate r h e n i u m atom w i t h six of the nine hydrogens at the corners of a trigonal prism, w i t h r h e n i u m at its center and the r e m a i n i n g three hydrogens beyond the centers of the rectangular faces (16). T h e hydrogen elemental analysis b y a t h e r m a l decomposition technique supported a H : R e = 8.7 a n d by a combustion technique, a H : R e = 8.9 (16). T h e magnetic susceptibility for potassium rhenium h y d r i d e (18) was found to be temperature independent f r o m 80° to 295°K, w i t h a x of -64 ± 10 X 1 0 - cgs/mol, uncorrected for the core diamagnetism. After these corrections were a p p l i e d , a small positive value was calculated, i.e., x = +25 X 1 0 - c g s / m o l , entirely consistent w i t h r h e n i u m i n the +7 oxidation state. T h e ir spectrum of K R e H showed two intense bands, one i n the metal-hydrogen stretching region at 1846 c m and the second at 735 c m i n the metal-hydrogen b e n d i n g region (15). 2

9

4

2

2

2

2

8

9

9

6

m

m

6

2

9

- 1

- 1


370


Potassium technetium h y d r i d e was formed b y the reduction of a m m o n i u m pertechnate w i t h potassium i n a m i x e d solvent of anhydrous e t h y l e n e d i a m i n e absolute ethanol c o n t a i n i n g 2% potassium ethoxide (19).

9

was similar

to K R e H i n its c h e m i c a l reactivity, its structure, a n d i r spectrum.

According

2

K TcH 2

9

to the x-ray powder diffraction evidence, K T c H was isostructural with K R e H . 2

9

2

T h e i r spectrum of K T c H , scanned f r o m 4000 to 400 c m 2

9

- 1

9

, was precisely the

same as the pattern observed for K R e H except that for K T c H , a l l the bands 2

were shifted a p p r o x i m a t e l y 50 c m

9

- 1

2

lower.

m e t a l - h y d r o g e n b o n d was weaker for K T c H 2


9

T h i s shift i n d i c a t e d the transition than for K R e H

9

2

to e x p l a i n the greater c h e m i c a l reactivity of K T c H . 2

a n d was used

9

Like K R e H , K T c H

9

2

9

2

9

reacted with water, giving off hydrogen and leaving behind a precipitate, presumably the transition metal.

K T c H was soluble i n strong aqueous alkali w i t h 2

9

o n l y m i n o r decomposition.

M-Re-H

Systems Where M = Na, K,

or(C H ) N 2

5

4

T h e s o d i u m salt, the quaternary a m m o n i u m salt, a n d a m i x e d s o d i u m potassium salt of nonahydridorhenate(VII), as well as a new route to the formation of K R e H , were reported (20). 2

9

N a R e H was formed b y reducing an ethanolic 2

9

solution of s o d i u m perrhenate w i t h sodium according to the f o l l o w i n g e q u a tion: excess N&

NaRe0

— •

4

Na ReH 2

9

+ NaOC H 2

5

+ NaOH

C H OH 2

5

T h e ternary h y d r i d e was p u r i f i e d b y reprecipitation f r o m aqueous methanolic sodium hydroxide.

N a R e H was soluble i n water and methanol, slightly soluble 2

9

i n ethanol, a n d insoluble i n 2-propanol, acetonitrile, ether, a n d T H F .

Decom-

position started at approximately 2 4 5 ° C w h e n heated i n a v a c u u m , w i t h the evolution of hydrogen and sodium as the temperature increased.

N a R e H was 2

9

a precursor for the preparation of the t e t r a e t h y l a m m o n i u m salt, the potassium salt, a n d the m i x e d potassium sodium salt of nonahydridorhenate(VII). [ ( C H 5 ) 4 N ] R e H was formed b y the metathesis reaction between N a R e H 2

2

9

2

9

a n d [ ( C H 5 ) N ] S 0 4 , a n d the product was p u r i f i e d b y reprecipitation w i t h ace2

tonitrile.

4

2

[ ( C H ) N ] R e H was soluble i n water, ethanol, 2-propanol, a n d ac2

5

4

2

9

etonitrile but insoluble i n ether a n d T H F .

T h e r m a l decomposition i n a v a c u u m

o c c u r r e d at 1 1 5 ° - 1 2 0 ° C , g i v i n g off hydrogen a n d ethane. T h e interesting product formed b y the treatment of a solution of N a R e H 2

w i t h excess K O H , followed b y precipitation w i t h methanol, was not K R e H 2

rather N a K R e H .

9

9

but

T h e x-ray p o w d e r diffraction pattern showed clearly that

9

the m i x e d cation ternary h y d r i d e was not a m i x t u r e of N a R e H a n d K R e H . 2

9

2

T h e formation of K R e H from N a R e H took a more circuitous route. 2

9

2

9

first was converted to B a R e H , followed b y the formation of K R e H 9

2

metathesis reaction between B a R e H a n d K S 0 . 9

2

4


9

Na ReH 2

9

9

b y the

25.

371

Ternary Hydrides of Some Rarer Pt Metah

MOYER E T AL.

Magnesium-Nickel-Hydrogen

System

R e i l l y a n d W i s w a l l (21 ) reported the synthesis of M g N i H by reacting the M g N i intermetallic c o m p o u n d w i t h hydrogen at 300 psi and 325°C, according to the f o l l o w i n g c h e m i c a l equation: 2

4

2

Mg Ni(s) + 2 H M N i H ( s ) 2

2

g 2

4

T h e ternary h y d r i d e was f o r m e d also at a reduced pressure a n d temperature of


200 psi a n d 200° C , respectively, after several cycles of h y d r i d i n g and d e c o m position.

M g N i H , a rust-colored solid w i t h a nonmetallic luster, reacted 2

4

sluggishly w i t h water but more vigorously w i t h nitric a c i d solution, g i v i n g off hydrogen.

Mg NiH 2

appeared to be unreactive to air u p o n short exposure.

4

T h e x-ray diffraction powder pattern for M g N i H was indexed on the basis 2

4

of a tetragonal crystal system w i t h unit cell dimensions of α = 6.464

and c =

7.033 A . T h e measured density was 2.57 g / c m , compatible w i t h four f o r m u l a 3

units of M g N i H 2

4

per unit cell.

Calcium-Silver-Hydrogen

System

A new ternary h y d r i d e of C a A g H was f o r m e d by either h y d r i d i n g the i n termetallic C a A g alloy at 5 7 5 ° - 6 0 0 ° C for 16-18 hr or reacting C a H and silver in a 1:2 molar ratio at 6 0 0 ° - 6 5 0 ° C i n a hydrogen atmosphere for 16 hr (22). T h e x-ray powder d i f f r a c t i o n pattern for C a A g H was indexed orthorhombic w i t h unit c e l l dimensions of α = 5.45 , b = 5.19 , and c = 9.86 . T h e density for C a A g H was 6.10 g / c m and was compatible w i t h four f o r m u l a units per unit cell. A comparison of the magnetic susceptibility of the C a A g intermetallic a n d C a A g H showed a shift f r o m a net positive or paramagnetic susceptibility i n the former to a net negative or diamagnetic susceptibility i n the latter. It has been speculated that electrons f r o m the hydrogen fill u p holes i n the conduction b a n d i n the C a A g that are responsible for the spin paramagnetism a n d thus suppress the susceptibility (22). 2

2

2

2

3

2

2

2

2

Ca-M-Hand

Sr-M-HSystems

Where M=

Group VIIIB Metal

S r P d H , S r P d H , a n d C a 3 P d H were reported by Stanitski a n d T a n a k a (23). S r P d H a n d S r P d H were f o r m e d by reacting stoichiometric mixtures of S r H a n d p a l l a d i u m for 10 hr at 7 6 0 ° C a n d 600 T o r r H for S r P d H and at 8 0 5 ° C a n d 625 T o r r H for S r P d H . Both ternary hydrides were black, crys talline, nonvolatile solids and were reactive to water or acidic solutions evolving hydrogen. S r P d H also was formed by hydrogénation of the S r P d intermetallic alloy. X - r a y powder diffraction analysis showed that the metal atoms i n S r P d H were arranged i n a cubic M g C u , Laves-phase array w i t h the unit cell length of 7.97 A. C a P d H was f o r m e d by a solid state reaction between C a H a n d p a l l a d i u m at 850° C i n H at 625 T o r r . T h e x-ray powder pattern for C a P d H 2

2

4

2

2

2

4

4

2

2

2

2

2

4

2

2

2

2

3

2

4

2

2


3

2

4

372


was indexed body-centered c u b i c w i t h a = 5.22 A . Ca Pd H 3

2

S r P d H , S r P D H , and 2

2

4

were either diamagnetic or weakly paramagnetic.

4

T h e ternary hydrides C a I r H , S r I r H , C a R h H , S r R h H , C a R u H , and 2

5

2

5

2

5

2

5

2

6

S r R u H were f o r m e d b y reacting the alkaline earth b i n a r y h y d r i d e w i t h the 2

6

p l a t i n u m group metal (24).

H e r e , the conditions were a temperature of 800°C

i n a p p r o x i m a t e l y 1 a t m H for about 12 hr. 2

L i k e the c a l c i u m - p a l l a d i u m a n d

s t r o n t i u m - p a l l a d i u m systems, these hydrides were nonvolatile and reacted w i t h water or acidic solutions, with the evolution of hydrogen.

Structural studies were


c a r r i e d out b y x-ray d i f f r a c t i o n a n d neutron diffraction analysis.

T h e x-ray

diffraction powder pattern for each of the six was indexed on the basis of a face-centered cubic (24), and the respective c e l l dimensions are g i v e n i n T a b l e I. Structural studies showed that the metal atoms were arranged i n a fluorite-type lattice consistent w i t h the space group F m 3 m , wherein the alkaline earth atoms were occupying the fourfold sites and the rarer platinum metals were occupying the eightfold sites. D e u t e r i u m sites for S r I r D a n d S r R u D were located f r o m neutron d i f 2

5

2

6

fraction studies, a n d the positions that gave the best fit (24) are s u m m a r i z e d i n T a b l e II. W i t h these coordinates, bond distances also were determined and are shown i n T a b l e III. T h e transition elements were viewed as six coordinate w i t h respect to d e u t e r i u m , where the atomic ratios were D : R u = 6 for S r R u D 6 a n d 2

D : I r = 5 plus one r a n d o m vacancy for S r I r D . 2

T a b l e I. Hydride Ca Sr Ca Sr Ca Sr a

b

5

5

2

2

5

5

2 2

T e r n a r y H y d r i d e P h y s i c a l Properties Cell Dimension

Color

IrH IrH RhH RhH RuH RuH

2

2

6

6

5

0

Black Black Black Black L i g h t Green L i g h t Green

7.29 7.62 7.24 7.60 7.24 7.60

Density, Exp.

g/cc Calc.

4.80 5.46 3.40 4.20 3.32 4.25

4.85 5.56 3.31 4.24 3.31 4.24

b

Cubic crystal system. Calculation based on four formula units per unit cell.

T a b l e II. Atom Sr Ir, R u D

S t r u c t u r a l Parameters for S ^ I r D s a n d S ^ R u D g (Space G r o u p Fm?>m) Position

Multiplicity

0

± (V , V , V ) (0,0,0) ±(V ,0,0) ±(0,V ,0) ±(0,0,V ) 4

4

4

8 4

4

4

24

4

9

Plus face centering, i.e., (0, V2, V2) and permutations should be added to each atomic position.


25.

T a b l e III.

B o n d Distances (in A) for the S r M D 2

M-D Sr-D Sr-M


Table IV.

ρ (ohm-cm)

Ir Rh Ru Ca Sr

6.1 4.7 10 4.6 25

Χ 10" Χ 10" X 10" Χ 10" Χ 10"

x

Structure

Ir

Ru

1.70 2.70 3.30

1.69 2.69 3.29

E l e c t r i c a l Resistivity at R o o m

Metal

a

373


MOYER E T AL.

Temperature

Ternary Hydride

a

Ca Ca Ca Sr Sr Sr

6 6 6 6

IrH RhH RuH IrH RhH RuH

2

2

6

2 2

p(ohm-cm) >10 -10 > 10 >10 -10 >10 7

5

2

5

2

6

6

6

5

5

7

6

Ref. 41.

A l l of the above ternary hydrides w i t h i r i d i u m , r h o d i u m , a n d r u t h e n i u m as the second metal showed weak temperature-independent paramagnetism or d i a m a g n e t i s m between 77° a n d 300°K (24).

T h e electrical resistivities of the

ternaries showed a sharp increase f r o m those of the i n d i v i d u a l metallic constit uents, as is presented i n T a b l e I V . These trends toward appreciably higher resistivities i n the ternary h y d r i d e suggest that hydrogénation has m o d i f i e d the electron population of the conduction bands of the metals. Eu-M-Hand

Yb-M-H

Systems Where M = Ru

T h e results on the alkaline e a r t h - g r o u p V I I I B ternary h y d r i d e systems suggested that systems where the alkaline earth is replaced b y e u r o p i u m or y t t e r b i u m w o u l d be worthy of study for several reasons. First of all, the structural similarities between E u H , Y b H , and C a H , S r H , and B a H (all orthorhombic) and between L i E u H a n d L i S r H (both perovskite) suggested that the rare earth metals m i g h t substitute at alkaline-earth metal sites. Secondly, the distinctive magnetic character of the two rare earth metals, e u r o p i u m and ytterbium, w i t h well-defined atomic moments arising f r o m relatively w e l l shielded 4 / electrons seemed to offer a w a y to study valence states f r o m data obtained b y magnetic susceptibility measurements. I n particular, the tendencies of these rare earth metals to f o r m both di-valent a n d tri-valent compounds raised the question as to how hydrogénation w o u l d affect these preferences. Finally, there was interest i n further investigating the shift i n electrical conductivity that already had been i d e n t i f i e d i n the a l k a l i n e e a r t h - r a r e r p l a t i n u m m e t a l - h y d r o g e n systems a n d w h i c h might offer evidence concerning the k i n d of electron exchange participated i n b y the hydrogens. T h e remainder of this article w i l l be concerned w i t h the 2

3

2

2

2

2

3


374



background, experimental techniques, and interpretation of results obtained on investigations c a r r i e d out so far i n the laboratory of the senior author of this chapter. T h e r e has been some previous work both on b i n a r y hydrides of e u r o p i u m a n d y t t e r b i u m a n d on b i n a r y alloys of e u r o p i u m and y t t e r b i u m w i t h p l a t i n u m group metals, w h i c h should be mentioned as a prelude to any consideration of the e u r o p i u m or ytterbium ternary hydride systems. T h e hydrides of e u r o p i u m a n d y t t e r b i u m are distinctive i n comparison w i t h the other lanthanide-series hydrides i n that it has not been possible to prepare any hydrides higher than the d i h y d r i d e at 1 a t m H (25). F u r t h e r m o r e , the E u H a n d Y b H have the orthor h o m b i c structure like the alkaline earth dihydrides, i n contrast to the cubic fluorite structure that is favored by the other lanthanide dihydrides. E u H is ferromagnetic w i t h a C u r i e temperature of about 25°K; above this temperature, its susceptibility can be fitted to a W e i s s - C u r i e law which yields an effective Bohr magneton n u m b e r quite close to that expected for E u (26). Y b H has been reported as being weakly paramagnetic w i t h an order of magnitude w h i c h is felt to reflect the theoretically zero-atomic moment for Yb " " (27). There is evidence of a n increase i n magnetic susceptibility for Y b H (28). T h e electrical resistivity of Y b H (29) has been shown to be of the order of m a g n i t u d e of 1 0 o h m c m , w h i c h is some 12 orders of magnitude greater than pure y t t e r b i u m metal (30). There are no values reported for the electrical resistivity of E u H , although it is presumably an insulator (26). 2

2

2

2

2 +

2

2

1

2 5 5

7

2

2

T h e question as to the electronic configuration of the hydrogen i n E u H and Y b H is still open. T h e magnetic studies by W a l l a c e et al. (26, 27) and the conductivity studies on Y b H by H e c k m a n and H i l l s (29) have been interpreted as f a v o r i n g an anionic or H ~ m o d e l for the hydrogen. Môssbauer studies by M u s t a c h i on both of these hydrides also y i e l d e d results that support the anionic m o d e l (31 ). H o w e v e r , there is a p r o b l e m w i t h the inference w h e n t r y i n g to explain the relatively h i g h C u r i e temperature (25°K) i n E u H . A c c o r d i n g to theories of cooperative magnetic behavior, the exchange effects necessary to p r o d u c e ferromagnetism require the conduction electrons of the metals; any r e m o v a l of these electrons i n h y d r i d e formation might be expected to suppress the ferromagnetism. Explaining the ferromagnetism while retaining the anionic model requires the more speculative arguments of either direct exchange between europium ions or an indirect routing of exchange via the H ~ ions (26,31 ). There are other lanthanides where the experimental evidence appears to favor a protonic m o d e l . Schreiber a n d Cotts (32) a n d K o p p a n d Schreiber (33) concluded f r o m N M R data on l a n t h a n u m - h y d r o g e n and c e r i u m - h y d r o g e n that these systems were described better by the protonic model. 2

2

2

2

T h e properties of some rare-earth binary alloys w i t h p l a t i n u m group metals are also important i n v i e w of the role they can play i n the c h a i n of p r e p a r i n g ternary hydrides. M a n y of the alloys of the series R - M , where R is a rare earth element a n d M is a G r o u p V I I I B metal, have been investigated structurally and magnetically. T h e alloys w i t h i r i d i u m a l l have cubic structures, whereas those


25.

375


MOYER ET AL.

w i t h r u t h e n i u m and o s m i u m are hexagonal as long as the rare earth is heavier than n e o d y m i u m .

T h e cubic structures are of the C 1 5 - t y p e Laves phase w h i l e

the hexagonal structures have the C 1 4 - t y p e Laves phase (34).

T h e alloys that

were studied magnetically (35) were ferromagnetic, w i t h C u r i e temperatures v a r y i n g systematically f r o m close to zero to 90° Κ and then back to zero as the rare earth metal progressed f r o m c e r i u m to l u t e t i u m . T h e alloys specifically included:

Celr , Prlr , PrOs , PrRu , N d l r , NdOs , N d R u , Smlr , SmOs , 2

2

2

2

2

2

2

2

2

Eulr , Gdlr , GdOs , GdRu , Tblr , TbOs , Dylr , DyOs , HoIr , HoOs , Erlr , 2

2

2

2

2

E r O s , T m l r , Y b l r , and L u R u . Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 17, 2017 | http://pubs.acs.org Publication Date: June 1, 1978 | doi: 10.1021/ba-1978-0167.ch025

2

2

2

2

2

2

2

2

2

2

T h e ferromagnetism was attributed to the

exchange interaction between conduction electrons and the spin of the 4/-shell electrons.

E u l r was reported as h a v i n g a large (77° K ) C u r i e temperature and 2

an extremely small saturation moment.

However, later work suggested that the

ferromagnetism m a y have been caused by the presence of E u O as an i m p u r i t y (36).

Some more recent results on E u l r w i l l be discussed later i n connection 2

w i t h attempts to hydrogenate it. Experimental Synthesis. E u r o p i u m and y t t e r b i u m metals were p u r i f i e d by v a c u u m distillation at 800° C . T a n k hydrogen was p u r i f i e d by passing the gas through a heated p a l l a d i u m tube filter, M o d e l H - l - D H , purchased f r o m Mattney Bishop, Inc. T h e usual synthesis route first was to prepare europium or ytterbium hydride b y heating the metals i n approximately 1 a t m H at 500° C . T e r n a r y hydrides were then prepared b y heating a compressed pellet containing a homogenous m i x t u r e of powders of e u r o p i u m or y t t e r b i u m h y d r i d e a n d the rarer p l a t i n u m metal at 800° C for approximately 18 hr and i n approximately 1 a t m H . Metals were h a n d l e d i n a glove bag i n a protective atmosphere of argon; the hydrides were handled i n a nitrogen atmosphere. T h e E u l r alloy was prepared by direct c o m b i n a t i o n of the metals. E u r o p i u m chips, Vs i n . on edge were placed i n a U in.-diameter cavity of a die. I r i d i u m metal powder, —325 mesh a n d 99.9% pure, was s p r i n k l e d over the rare earth element, a n d the m i x t u r e was compressed at 5000 psi. T h e compressed pellet was placed i n a m o l y b d e n u m boat, w h i c h then was transferred to a quartz sleeve, followed b y insertion into a quartz reaction tube. T h e tube was attached to a glass vacuum line and evacuated. Argon was added to approximately 1 atm; a n d the compressed pellet was heated to 900° C and held at the temperature for 14 hr. T h e product was air quenched to room temperature. T h e product was crushed i n an agate ball m i l l , compressed into a pellet again, and reheated i n the same manner as before. H y d r o g e n A n a l y s i s . T h e t h e r m a l decomposition technique was used to determine the hydrogen elemental composition. T h e sample was heated i n vacuo to 9 2 5 ° C and was m a i n t a i n e d at that temperature until a l l evolved gas was transferred b y w a y of a Toepler p u m p to a calibrated gas buret. X - R a y D i f f r a c t i o n A n a l y s i s . X - r a y powder diffraction data for i n d e x i n g were obtained w i t h a G e n e r a l E l e c t r i c X R D - 6 diffractometer. Samples were sealed i n glass capillaries (0.5 m m o.d.) and exposed to nickel-filtered C u K a r a diation. K C l or i r i d i u m was used as an internal standard. X - r a y powder d i f fraction intensity data were obtained with a General Electric X R D - 5 unit. Here, 2

2

2

l



376


the samples were m i x e d w i t h a protective coating of petroleum jelly, smeared on a glass slide, a n d exposed to n i c k e l - f i l t e r e d C u K a radiation. Intensity data were obtained b y measuring the area under the peaks on the chart paper w i t h a planimeter. Magnetic Susceptibility Measurements. M a g n e t i c susceptibilities were measured b y the F a r a d a y method a n d were accurate to ± 2 % . Samples, usually as powders, were placed i n a c y l i n d r i c a l T e f l o n boat h a v i n g an internal v o l u m e of 0.30 cc. Measurements were m a d e at 2963, 4357, 5724, 7077, a n d 8243 G , a n d at temperatures 7 7 ° - 2 9 5 ° K . It was possible to correct for ferromagnetic i m p u r i t i e s f r o m any f i e l d dependent effects. Electrical Resistivity Measurements. Electrical resistances were measured by the voltage-current method. T h e powder sample was compressed into a pellet w i t h a diameter of V i n . at 5000 psi. T h e pellet was placed oetween twoTbrass electrodes, a n d the electrical resistance of trie sample was d e t e r m i n e d f r o m the measurements of the current through the sample and the potential across the sample. Differential Thermal Analysis. H i g h temperature differential t h e r m a l analyses were obtained w i t h a D u p o n t M o d e l 1200 instrument. Samples were heated f r o m room temperature to 950° C at a rate of 2 0 ° C / m i n i n a slow stream of hydrogen. M o l y b d e n u m cups were used to hold the sample a n d a l u m i n a reference. T h e instrument was calibrated w i t h s o d i u m c h l o r i d e (mp 800° C ) . Ir Analysis. Ir spectra of E u R u H a n d Y b R u H were made w i t h a B e c k m a n Ir-12 spectrophotometer. T h e samples were scanned as K B r discs from 4000 to 200 c m " . 4

2

6

2

6

1

Results and Discussion Europium-Ruthenium-Hydrogen and Ytterbium-Ruthenium-Hydrogen Systems. E u R u H (37) a n d Y b R u H (38) were f o r m e d b y heating the re spective binary rare earth d i h y d r i d e and r u t h e n i u m i n a molar ratio of 2:1. T h e pellet c o n t a i n i n g the homogeneous m i x t u r e expanded substantially d u r i n g the reaction, accompanied by an absorption of approximately one mole of hydrogen per mole of r u t h e n i u m . E u R u H was a b r i c k red crystalline solid; Y b R u H was black. B o t h reacted to acidic solutions b y g i v i n g off hydrogen a n d p r e c i p itating ruthenium, and both were unreactive to the atmosphere for brief periods of time. Structural analyses b y x-ray diffraction techniques showed that as far as the arrangement of the metals were concerned, E u R u H was isostructural w i t h S r R u H w i t h α = 7.566 A, and Y b R u H was isostructural w i t h C a R u H e w i t h α = 7.248 A. 2

6

2

2

6

6

2

2

2

6

2

6

6

6

2

T h e magnetic susceptibility studies supported a +2 oxidation state for e u r o p i u m i n E u R u H and for y t t e r b i u m i n Y b R u H . F i g u r e 1 is a plot of the reciprocal of x , the corrected magnetic susceptibility per g-atom of e u r o p i u m vs. T , the absolute temperature of the E u R u H sample. A straight line fits the experimental points f r o m 85° to 296°K. T h e W e i s s - C u r i e law x = C /(T - Θ) was fitted b y x = 7 . 5 8 / Γ - 43. T h e constant C = 7.58 corre sponded to μ {( = 7.82 μ . T h i s value agreed w i t h E u h a v i n g a theoretical magnetic m o m e n t of 7.94 μβ. T h e r u t h e n i u m was believed to be i n the +2 ox idation state and was not contributing paramagnetically to the bulk susceptibility. 2

6

2

6

A

2

6

A

A

A

e

Β

A

2 +



25.

377


M O Y E R E T AL.

Figure 1.

Graph of 1/XA (emu/g-atom)~ EuzRuHs

l

vs. Τ (°K) for

T h e value of the Weiss constant 0 was 43 ± 1°K a n d suggested that E u R u H 2

becomes ferromagnetic at some temperature below 77°K.

6

T h e magnetic sus

ceptibility for Y b s R u H e appeared to be consistent w i t h di-valent ytterbium, w h i c h theoretically has zero atomic m o m e n t .

T h e small p a r a m a g n e t i s m observed

e x p e r i m e n t a l l y was assigned to Yb C>3 i m p u r i t y . 2

T h e m a g n i t u d e of the electrical resistivity as w e l l as its behavior w i t h t e m perature is shown i n T a b l e V . ρ = ροβ

Δ £

T h e data i n T a b l e V were fitted to the equation

/ * , where the activation energies Δ Ε were 0.15 e V for E u R u H a n d 2

τ

2

0.18 e V for Y b R u H . 2

Table V .

E l e c t r i c a l Resistivity

p(ohm-cm)

Τ(°Κ)

Yb RuH ρ (ohm-cm)

293 200 145 77

3.06 2.27 1.09 6.52

EU RUHQ

2

2

T(°K) 294 209 167 77

6

T h e hydrogénation process appears to have p r o d u c e d

6

2.5 1.2 4.1 4.0

ΙΟ ΙΟ Χ ΙΟ Χ ΙΟ

Χ

5

Χ

6 6 9

6

ΙΟ ΙΟ Χ ΙΟ Χ ΙΟ Χ

4

Χ

5


6 8

378


ternary hydrides w i t h semiconducting properties f r o m the constituent m e t a l l i c - t y p e electrical conductors. A profile of the differential thermal analysis of E u R u H is shown i n F i g u r e 2. T w o endotherms were observed upon heating the sample: an intense d i p at 9 0 3 ° C and weaker d i p at 7 9 4 ° C . U p o n cooling, two exotherms were found at 817° a n d 7 8 8 ° C . T h e 9 0 3 ° C endotherm was almost certainly caused b y the t h e r m a l decomposition of E u R u H . T h e endotherm at 7 9 4 ° C was assigned to the decomposition of E u H , a n d the exotherm at 7 8 8 ° C was believed to be caused b y the formation of E u H . T h e exotherm at 8 1 7 ° C was assigned c a u tiously to the formation of a h y d r i d e by a route involving a reaction between the intermetallic c o m p o u n d of e u r o p i u m or r u t h e n i u m or b y the c h e m i c a l c o m b i nation of e u r o p i u m , r u t h e n i u m , a n d hydrogen. 2

2

6

6

2


2

P r e l i m i n a r y interpretation of the i r spectra for E u R u H g and Y b R u H e suggested that there were absorptions that c o u l d be assigned to the r u t h e n i u m hydrogen stretching and bending vibrations. T h e results of the ir data are found in Table V I . 2

2

C h a t t a n d H a y ter (39) reported the results of ir spectra of several six-coordinate hydrido complexes of ruthenium i n the +2 oxidation state. They reported that h y d r i d o complexes that have one hydrogen show a band between 1750 and 1980 c m attributable to ruthenium-hydrogen stretch. A shift i n the stretching frequency of m o r e than 350 c m lower resulted w h e n a second hydrogen was placed i n the position trans to the first. F o r example, the absorption b a n d observed at 1976 c m for i r a n s - [ R u H I j o - C H ( P E t ) ) ] was assigned to the r u thenium-hydrogen stretching frequency, and the band at 1617 c m was assigned to the r u t h e n i u m - h y d r o g e n s t r e t c h i n g f r e q u e n c y for and the absorption bands located between 600-500 c m were assigned to r u t h e n i u m - h y d r o g e n b e n d i n g v i b r a t i o n (6R _H). U

- 1

U

E u r o p i u m - I r i d i u m - H y d r o g e n a n d Y t t e r b i u m - I r i d i u m - H y d r o g e n Systems. W h e n E u H or Y b H was heated w i t h i r i d i u m at 800° C i n approximately 1 a t m H , the intermetallic compounds E u l r or Y b l r , containing very little hydrogen, were produced. These products w i l l be referred to i n the discussion as E u I r H a n d Y b I r H . In the case of the e u r o p i u m - i r i d i u m system, χ was d e t e r m i n e d to be between 0.1 and 0.2. In contrast to the e u r o p i u m - a n d y t t e r b i u m - r u t h e n i u m ternary hydrides, the reaction of E u H or Y b H w i t h i r i d i u m failed to show the pellet e x p a n d i n g w h e n heated, and there was considerable hydrogen evolution. T h e x-ray diffraction patterns for both the E u I r H a n d Y b I r H showed a fee structure w i t h unit cell dimensions of a = 7.571 a n d a = 7.456 A , respectively. Structure factor analysis of the above products indicated that the m e t a l atoms i n both compounds were arranged i n a cubic C 1 5 - t y p e C u M g Laves phase. These findings are to be c o m p a r e d w i t h the w e l l - k n o w n Laves phase of E u l r and Y b l r (40) w i t h respective unit cell dimensions of 7.566 and 7.477 . As a check E u l r was prepared by heating the respective elements at 900° C i n an argon atmosphere. Results of the x-ray diffraction patterns showed fee structure with a = 7.570 A , but there was strong evidence from the patterns that the actual composition should more properly be described as a Laves phase deficient i n i r i d i u m , close to E u l r i 5. F u r t h e r m o r e , a finely d i v i d e d powder sample of the E u l r alloy i n a hydrogen atmosphere was heated slowly to 500° C over a period of 30 hr, held at 500° C for approximately 18 hr, and cooled to a p proximately 100° C over a period of 8 hr. N o hydrogen absorption, as noted by m a n o m e t r i c measurements, was observed. It has been observed recently that w h e n E u H was c o m b i n e d w i t h i r i d i u m i n a 2:1 molar ratio and heated to 6 5 0 ° - 7 0 0 ° C i n approximately 1 a t m H , a new ternary h y d r i d e was f o r m e d a c c o m p a n i e d by an absorption of hydrogen. T h e new ternary h y d r i d e phase was indexed fee and predicted to be isostructural w i t h S r I r H s . T h e upper limit of the reaction temperature is critical. T h e i r i d i u m - d e f i c i e n t Laves phase m e n t i o n e d above w i l l f o r m , accompanied by the evolution of hydrogen, should the reaction temperature approach 800° C . 2

2

2

2

2

2

2

x

2

x

x

2

2

2

x

2

2

2

2

2

2

2

2

T h e magnetic a n d electrical properties of E u l r and E u I r H were investi gated to see if any differences i n these properties could be detected between the 2

2

x


380


two materials. Over the temperature range from 7 7 ° to 2 9 5 ° K , the molar susceptibilities x of both materials appeared to be paramagnetic, with little difference between them. However, the magnitudes were such that the presence of even a few percent of E u O would be sufficient to render any quantitative in terpretation of these data subject to considerable uncertainty, a point which has been made previously by Bozorth et al. (35,36) in discussing their results on Eulr . The resistivity measurements indicated that both preparations were metallic conductors of the same order of magnitude. M


2

Literature Cited 1. Jaubert, G. F., French Pat. 327,878 (1902). 2. Jaubert, G. F., British Pat. 25,215 (1907). 3. Farber, E., "Chymia," Vol. 8, H. M. Leicester, Ed., p. 165, University of Pennsylvania, Philadelphia, 1962. 4. Newkirk, H. W., "A Literature Study of Metallic Ternary and Quaternary Hydrides," UCRL-51244, Rev. 1, Lawrence Livermore Laboratory, University of California, Livermore, 1975. 5. Van Mal, H. H., "Stability of Ternary Hydrides and Some Applications," Philips Res. Rep. Suppl. (1976) 1. 6. Messer, C. E., Eastman, J. C., Mers, R. G., Maeland, A. J., Inorg. Chem. (1964) 3, 776. 7. Messer, C. E., Hardcastle, K., Inorg. Chem. (1964) 3, 1327. 8. Greedan, J. E., J. Cryst. Growth (1970) 6, 119. 9. Ashby, E. C., Kovar, R., Arnott, R., J. Am. Chem. Soc. (1970) 92, 2182. 10. Farr, I. D., Inorg. Nucl. Chem. (1960) 14, 202. 11. Lundberg, L. B., Cromer, D. T., Magee, C. B., Inorg. Chem. (1972) 11, 400. 12. Graefe, A. F., Robeson, R. K., J. Inorg. Nucl. Chem. (1967) 29, 2917. 13. Floss, J. G., Grosse, Α. V., J. Inorg. Nucl. Chem. (1960) 16, 37. 14. Ginsberg, A. P., Miller, J. M., Cavanaugh, J. R., Dailey, B. P., Nature (1960) 185, 528 15. Ginsberg, A. P., Miller, J. M., Koubek, E., Am. Chem. Soc. (1961) 83, 4909. 16. Abrahams, S. C., Ginsberg, A. P., Knox, K., Inorg. Chem. (1964) 3, 558. 17. Knox, K., Ginsberg, A. P., Inorg. Chem. (1964) 3, 555. 18. Ibid (1962) 1, 945. 19. Ginsberg, A. P., Inorg. Chem. (1964) 3, 567. 20. Ginsberg, A. P., Sprinkle, C. R., Inorg. Chem. (1969) 8, 2212. 21. Reilly, J. J., Wiswall, R. H., Inorg. Chem. (1968) 7, 2254. 22. Mendelsohn, M. H., Tanaka, J., Lindsay, R., Moyer, R. O., Jr., Inorg. Chem. (1975) 14, 2910. 23. Stanitski, C., Tanaka, J., J. Solid State Chem. (1972) 4, 331. 24. Moyer, R. O., Jr., Stanitski, C., Tanaka, J., Kay, M., Kleinberg, R., J. Solid State Chem. (1971)3, 541. 25. Mueller, W. M., "Metal Hydrides," W. M. Mueller, J. P. Blackledge, G. C. Libowitz, Eds., p. 384ff, Academic, New York, 1968. 26. Zanowick, R. L., Wallace, W. E., Phys. Rev. (1962) 126, 537. 27. Wallace, W. E., Kuhota, Y., Zanowick, R. L., "Non Stoichiometric Compounds," ADV. C H E M . SER. (1963) 39, 122ff. 28. Hardcastle, Κ. I., Warf, J. C., Inorg. Chem. (1966) 5, 1728. 29. Heckman, R. C., Hills, C. R., Bull. Am. Phys. Soc. (1965) 10, 126. 30. Kayser, F. X., Soderquist, S. D., Scr. Metall. (1969) 3, 259. 31. Mustachi, Α., J. Phys. Chem. Solids (1975) 35, 1447. 32. Schreiber, D. S., Cotts, R. M., Phys. Rev. (1963) 131, 1118. 33. Kopp, J. P., Schreiber, D. S., J. Appl. Phys. (1967) 38, 1373.



25.

MOYER ET AL.


381

34. Compton, V. B., Matthias, B. T., Acta Crystallogr. (1959) 12, 651. 35. Bozorth, R. M., Matthias, B. T., Suhl, H., Corenzuit, E., Davis, D. D., Phys. Rev. (1959) 115, 1595. 36. Matthias, B. T., Bozorth, R. M., Van Vleck, J. H., Phys. Rev. Lett. (1961) 1,160. 37. Thompson, J. S., Moyer, R. O., Jr., Lindsay, R., Inorg. Chem. (1975) 14, 1866. 38. Lindsay, R., Moyer, R. O., Jr., Thompson, J. S., Kuhn, D. Α., Inorg. Chem. (1976) 15, 3050. 39. Chatt, J., Hayter, G., J. Chem. Soc. (1961) 2605. 40. Elliott, R. P., Proc. Rare Earth Res., 4th, NewYork,1965, L. Eyring, Ed., p. 224, Gordon and Breach. 41. E. W. Washburn, Ed., "International Critical Tables of Numerical Data, Physics, Chemistry, and Technology," p. 104, 1st ed., Vol. 1, McGraw-Hill, New York, 1926. RECEIVED August 1, 1977.


Transition Metal Hydrides - American Chemical Society

Recommend Documents