Inorganic Compounds with Unusual Properties

11

Non-Stoichiometric Liquid Enclosure

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Compounds ("Liquid Clathrates") JERRY L. ATWOOD Department of Chemistry, University of Alabama, University, Ala. 35486 JIM D. ATWOOD School of Chemical Sciences, University of Illinois, Urbana, Ill. 61801

Compounds of the general formulation M[Al (CH ) X]— where M = alkali metal, tetraalkylammonium ion and X = N -, SCN , SeCN , Cl , Br , I—react in a visually dramatic fashion with small aromatic molecules to form non-stoichiometric liquid complexes. In the most favorable situation, as many as 16 benzene molecules are trapped per anionic unit. Because of similarity to the well known solid-state clathrates, the designation "liquid clathrate" is used for the new substances. The term is not meant to imply order as in the solid state, but to convey the method of interaction of M[Al (CH ) X] with aromatic molecules. The liquid clathrate may consist of either roughly spherical or layerlike domains; the latter is supported by the x-ray crystallographically determined structure of K[CH Se{Al(CH ) } ] . 2C H . 2

-

-

-

-

3 6

-

3

2

3 6

3

6

3 3

3

6

he interactions of o r g a n o m e t a l l i c m o l e c u l e s w i t h s m a l l h y d r o c a r b o n substrates h a v e b e e n s t u d i e d extensively b o t h i n s o l u t i o n a n d i n t h e s o l i d state.

I n t h e latter, t h e interactions a r e necessarily q u i t e strong,

a n d t h e y m a y b e d i v i d e d i n t o t w o extreme categories.

T h e r e are m o l e -

cules w h i c h i n v o l v e a s t r o n g d i r e c t i o n a l b o n d b e t w e e n the m e t a l i o n a n d the a r o m a t i c m o i e t y [e.g., i n

Cr(C H )2 G

6

(1, 2) o r i n t h e A g C 1 0

4

· aro-

m a t i c systems (3)1, a n d t h e r e a r e arrays f o r w h i c h there is n o specific i n t e r a c t i o n b e t w e e n t h e m e t a l a t o m itself a n d t h e a r o m a t i c center t h e case p r e s e n t e d b y s i m p l e m o l e c u l e s o f s o l v a t i o n (4, 5 ) ] .

[e.g.,

O n the other

h a n d , t h e d i v e r s i t y o f systems r e p o r t e d f o r the l i q u i d state is so great as to d e f y s u m m a t i o n , b u t some o f the most i m p o r t a n t h a v e i n v o l v e d subtle 112 King; Inorganic Compounds with Unusual Properties Advances in Chemistry; American Chemical Society: Washington, DC, 1976.

11.

113

Liquid Clathrates

ATWOOD A N D ATWOOD

i n t e r p r e t a t i o n s of d e t a i l e d n u c l e a r m a g n e t i c r e s o n a n c e (6, 7,

( N M R ) studies

8).

T h e class of substances w e refer to as " l i q u i d c l a t h r a t e s " e x h i b i t s a n e w t y p e of s t r o n g o r g a n o m e t a l l i c - a r o m a t i c i n v o l v e m e n t

(9,

10,

11).

H o w e v e r , b e f o r e this b e h a v i o r is d e s c r i b e d i n d e t a i l , i t is necessary

to

r e v i e w t h e o r i g i n a n d c h a r a c t e r i z a t i o n of t h e p a r e n t m o l e c u l e s .


Preparation

of

M[A^R X] 6

Ziegler a n d co-workers

first

(12)

r e p o r t e d i n 1960 t h a t a l u m i n u m

a l k y l s react w i t h a l k a l i m e t a l h a l i d e s to f o r m e i t h e r 1:1 or 2 : 1 AIR, + 2A1R (Reactions 1 and 2 ) .

3

+

complexes

M X -> M [ A 1 R » X ]

(1)

M X —> M [ A 1 R X ]

(2)

2

6

T h e s e substances w e r e i n i t i a l l y of interest b e c a u s e

t h e y p r o v i d e d a neat i n o r g a n i c s t u d y of t h e r e l a t i v e i m p o r t a n c e of t h e lattice energies of M X a n d M [ A 1 R X ] or M [ A 1 R X ] . T h u s , L e h m k u h l 3

(13)

2

6

c o n c l u d e d t h a t c o m p l e x a t i o n occurs m o s t r e a d i l y w h e n t h e i o n i c

r a d i u s of t h e a l k a l i m e t a l is l a r g e , t h e a l k y l c h a i n is short, a n d the c o m p l e x i o n is s m a l l . A l t h o u g h t h e l o g i c a l extension of the p r e p a r a t i v e m e t h o d to i n c l u d e a l k a l i m e t a l p s e u d o h a l i d e s w a s m e n t i o n e d i n the o r i g i n a l p a p e r (12),

no

w e l l d e f i n e d complexes of this sort w e r e n o t e d u n t i l the 1971 reports b y o u r g r o u p ( 14) a n d s u b s e q u e n t l y b y D e h n i c k e et al.

Anionic

Structure

of

(15).

M[A/ R X] 2

6

I n 1963, A l l e g r a a n d P e r e g o 2

first

(16)

h a l i d e c o m p l e x , t h a t of K [ A l ( C H 2

r >

) F]. r )

r e p o r t e d s t r u c t u r e of a 2 : 1 T h e y f o u n d t h a t the a n i o n

exhibited a completely linear A l - F - A l linkage, a n d they postulated both sp h y b r i d i z a t i o n of the

fluorine

atom a n d d orbital participation b y the

a l u m i n u m a t o m i n o r d e r to e x p l a i n the o b s e r v e d b o n d lengths a n d angles. O u r g r o u p has f o u n d p r e c i s e l y the s a m e g e o m e t r y a b o u t the

fluorine

atom i n Κ [ A l ( C H ) F ] · C H 2

3

6

6

6

(Structure

s i t u a t i o n m u s t b e e n v i s i o n e d f o r the C l " , B r ' , a n d Γ b r i d g e d A l t h o u g h the 2:1 complexes

l)

( 5 ) , b u t a different complexes.

of these ions w e r e n o t s t u d i e d b y

x-ray

c r y s t a l l o g r a p h y , s i m p l e h y b r i d i z a t i o n a r g u m e n t s suggest t h a t t h e c h l o r i n e , b r o m i n e , a n d i o d i n e atoms w o u l d use essentially ρ orbitals i n a b r i d g i n g situation (Structure 2).

Structures s u c h as t h a t of the r e c e n t l y d e t e r

m i n e d b r o m o n i u m y l i d e ( S t r u c t u r e 3 ) (17)

provide structural verification

of this i d e a .

King; Inorganic Compounds with Unusual Properties Advances in Chemistry; American Chemical Society: Washington, DC, 1976.

114

INORGANIC

COMPOUNDS

WITH

UNUSUAL

PROPERTIES

θ X

R A1 3

F

R A1

AIR3

X 1 Downloaded by UNIV OF CALIFORNIA SAN DIEGO on April 13, 2016 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/ba-1976-0150.ch011

A1R

3

=

Cl-, Br-

3

I~; a ~

90'

2

F o r t h e 2:1 p s e u d o h a l i d e c o m p l e x e s , t w o cases m a y b e differentiated w i t h reference to [ A L R e S C N ] " . the s o l i d state for R = — C H

3

S t r u c t u r e 4 appears to b e f a v o r e d i n from detailed I R and R a m a n

spectral

studies ( 18) a n d b y a n a l o g y to t h e s t r u c t u r e of K [ A l 2 ( C H ) N ] (9, J O ) . 3

e

3

6


11.

Liquid

ATWOOD A N D ATWOOD

115

Clathrates

H o w e v e r , s y n t h e t i c w o r k n o w i n d i c a t e s t h a t S t r u c t u r e 5 is d o m i n a n t a t h i g h t e m p e r a t u r e s ( 1 9 ) a n d for R = — C H 2

5

or higher a l k y l chain length

(20). D i r e c t s t r u c t u r a l e v i d e n c e is p r o v i d e d b y t h e x - r a y d i f f r a c t i o n s t u d y of K [ A 1 ( C H ) N ] ( 9 , 10) 2

3

6

i n w h i c h (as w a s i n d i c a t e d p r e v i o u s l y ) t h e

3

a z i d e i o n has a s i n g l e n i t r o g e n a t o m b r i d g e ( S t r u c t u r e 6 ) . A n i n t e r e s t i n g s i d e l i g h t is t h e i n f o r m a t i o n r e v e a l e d a b o u t t h e m e t h y l g r o u p c o n f o r m a t i o n ; t h e r e are t w o a n i o n i c p o s s i b i l i t i e s w h i c h h a v e C and C

point symmetries.


8

2 v

V i e w e d d o w n the nitrogen atom chain they

a p p e a r as:

W e l l e r a n d D e h n i c k e (18, that

the

anions

in

3

[ A 1 ( C H ) S C N ] a r e of C 2

3

u n i t of

4

2

3

6

6

and

3

K [ A 1 ( C H ) N ] , there 2

3

6

[ A 1 ( C H ) N ] ~ i o n s : one of C 2

3

in

[N(CH ) ]3

4

s y m m e t r y . H o w e v e r , i n the c r y s t a l l o g r a p h i c

2v

6

asymmetric

d e t e r m i n e d f r o m s p e c t r o s c o p i c studies

21)

[N(CH ) ] [A1 (CH ) N ]

are

3

two

nonequivalent

s y m m e t r y a n d o n e of C

2v

3

8

symmetry.

T h e b o n d distances a n d angles i n b o t h f o r m s are q u i t e s i m i l a r , a n d t h e existence of b o t h types is i n d i c a t i v e of t h e closeness i n o v e r a l l e n e r g y of the t w o configurations i n s o l u t i o n . Definition

of Liquid

Clathrate

Behavior

T h e t e r m " l i q u i d c l a t h r a t e " is u s e d to d e s i g n a t e t h a t g r o u p of n o n s t o i c h i o m e t r i c c o m p o u n d s w h i c h f o r m u p o n the i n t e r a c t i o n of a r o m a t i c m o l e c u l e s w i t h c e r t a i n M [ A 1 ( C H ) X ] moitiés. W i t h M — a l k a l i m e t a l 2

ion and X =

3

6

N " , S C N " , or S e C N " , M [ A l ( C H ) X ] is a n a i r - s e n s i t i v e 3

2

solid, whereas w i t h M =

3

e

tetraalkylammonium ion and X =

C l " , B r " , or T ,

M [ A 1 ( C H ) X ] is a n a i r - s e n s i t i v e l i q u i d . I n b o t h cases, i n t e r a c t i o n w i t h 2

3

6

t h e a p p r o p r i a t e a r o m a t i c substance p r o d u c e s a l i q u i d w h i c h is i m m i s c i b l e w i t h excess a r o m a t i c .

T h e aromatic molecules

i n the l i q u i d clathrate

a p p e a r to b e t r a p p e d m u c h as t h e y w o u l d b e i n a solid-state c l a t h r a t e ; t h e y c a n b e f r e e d b y l o w e r i n g t h e t e m p e r a t u r e a n d thus b e r e c l a i m e d u n c h a n g e d . T h e s e observations m a y b e s u m m a r i z e d b y t h e e q u i l i b r i u m

M[Al (CH )eX] + 2

8

high temp. η aromatic ^ M [ A 1 ( C H ) X ] · η aromatic low temp. liquid clathrate 2

3

6


(3)

116

INORGANIC

COMPOUNDS

Proposed Shape Theory of Liquid Clathrate

WITH

UNUSUAL PROPERTIES

Formation

I n f o r m a t i o n a b o u t t h e n a t u r e of l i q u i d clathrates m a y b e d e r i v e d b y t a b u l a t i n g those h a l i d e s a n d p s e u d o h a l i d e s that p r o m o t e t h e effect ( T a b l e I).

A l l t h e anions w h i c h m a y b e u s e d to f o r m a l i q u i d c l a t h r a t e a r e

b e l i e v e d to h a v e a n a n g u l a r g e o m e t r y (CH ) A1


3

3

>

A1(CH )

3

3

7 geometry

3

}

(CH ) A1 3

(Structure 7 ) , whereas a linear A1(CH )

3

3

8

( S t r u c t u r e 8 ) is c h a r a c t e r i s t i c of those anions w h i c h d o n o t

f o r m l i q u i d clathrates. T h e a n g u l a r s t r u c t u r e has t w o n o t e w o r t h y

fea-

t u r e s : t h e a n i o n has a n a p p r e c i a b l e d i p o l e m o m e n t , a n d there is a definite s e p a r a t i o n of o r g a n i c a n d i n o r g a n i c regions. T h u s , t h e negative c h a r g e is l a r g e l y l o c a l i z e d o n t h e v e r y accessible i n o r g a n i c e n d of the a n i o n , w h i l e the r a t h e r massive o r g a n i c r e g i o n is q u i t e f a r a w a y . W e r e p o r t e d p r e v i o u s l y ( I I ) that anions w i t h this geometry w i l l react w i t h m o l e c u l e s s u c h as b e n z e n e or toluene to f o r m l i q u i d complexes w h i c h c o n t a i n 1.5-13.0 a r o m a t i c m o l e c u l e s p e r a n i o n i c unit. Table I. Classification of Halide and Pseudohalide Ions in [ A l ( C H 3 ) X ] " as to the Formation of LiquidClathrates with Benzene 2

6

Does Form Liquid

Clathrate

Does Not Form Liquid

ClBrISCNSeCNN N0 -

Clathrate

F C N -

3

3

T h e n a t u r e of the i n t e r a c t i o n has b e e n r e l a t e d to t h e shape of the a n i o n i n M [ A 1 ( C H ) X ] ; i t w a s p r o p o s e d ( 1 0 , 11) t h a t a cage o r l a y e r 2

3

6

l i k e structure of o r i e n t e d anions is set u p w i t h c o u n t e r ions a n d a r o m a t i c molecules trapped inside. Constitution

of Liquid

Clathrates

T h e N M R spectra of a l l l i q u i d clathrates h a v e one f e a t u r e i n c o m m o n : t h e entire s p e c t r u m is s h i f t e d 0.2-0.5 p p m d o w n f i e l d r e l a t i v e to t h e p u r e a r o m a t i c substance.

H o w e v e r , this is t h o u g h t t o b e a b u l k


11.

Liquid

ATWOOD A N D ATWOOD

117

Clathrates

d i a m a g n e t i c effect, since i n e v e r y case t h e l i q u i d c l a t h r a t e is m o r e d e n s e t h a n the a r o m a t i c m o i e t y . F o r e a c h i n d i v i d u a l M [ A 1 ( C H ) X ] · a r o m a t i c , there is a m a x i m u m 2

3

6

a r o m a t i c / a n i o n r a t i o . T h e t a b u l a t i o n of l i q u i d c l a t h r a t e d a t a i n T a b l e I I illustrates the f o l l o w i n g (11):

(a)

the l a r g e r the c a t i o n , t h e greater t h e

n u m b e r of a r o m a t i c m o l e c u l e s i n the c l a t h r a t e ; ( b )

the more

electro

n e g a t i v e the h a l i d e i o n , t h e greater the n u m b e r o f a r o m a t i c m o l e c u l e s i n


Table I I .

Compositions of Various L i q u i d Clathrates Al-CH Proton Chemical Shift" 3

Compound

Aromatic

K[A1 (CH ) N ] Rb[AI (CH ) N l Cs[Al (CH ) N ] K[AU(CH,).NO,] Ce[Al,(CH,),NOi] [N(C H ) ][A1 (CH ) N0 ] [N(CH ) ][A1 (CH ) C1] [N(CH ) l[Al (CH ) I] [N(C H ) ][A1 (CH )J] [N(C H ) ][A1 (CH ) I] [N(C H ) ][A1 (CH ) I] [N(C H„) 1[A1 (CH )J] K[A1 (CH ) SCN] K[A1 (CH ) N ] Rb[Al (CH ) N ] Cs[Al (CH ) N ] [N(C H ) ][A1 (CH ) N0 ] [N(CH ) )[A1 (CH )6C1] [N(CH ) )[Al (CH ) Br] [N(CH ) ][A1 (CH ) I] [N(C H ) ][A1 (CH ) I] [N(C H ) ][A1 (CH )J] [N(C H ) )[Al (CH ) Br] [N(C H ) ][A1 (CH ) I] [N(C H„) ][A1 (CH ) I] [N(C H )(CH ) ][Al (CH ) I] [N(C H ) ][A1 (CH ) I] [N(C H ) ][A1 (CH ) I] [N(C H ) ][A1 (CH )J] [N(C Hn)4][Al (CH ) I] Cs[Al (CH ) N ] [N(C H ) ][Al (CH )J] [N(C H„) ][A1 (CH ) I] [Ν(Ο Η ) ][Α1 (ΟΗ ) Ι] 2

3

6

2

3

3

2

e

3

2

6

3

6

3

4

2

4

3

2

3

4

2

3

2

6

7

4

2

4

9

4

2

3

3

3

6

3

6

2

5

3

6

3

2

4

5

3

7

3

4

9

9

2

3

2

3

2

4

4

6

3

6

3

2

3

6

2

3

6

4

2

6

3

3

3

6

2

2

5

4

2

3

6

3

7

4

2

3

6

4

9

4

2

2

5

3

n

6

δ

η

4

6

3

e

ethylbenzene

3

5

2

3

6

2

4

5

6

6

3

4

4

3

2

4

2

toluene

3

6

4

4

3

3

3

3

3

2

6

2

2

2

6

3

4

2

3

e

2

3

6

6

3

4

5

benzene

s

3

e

3

2

p-xylene

3

4

2

3

6

4

2

3

6

m-xylene mesitylene

Maximum Ar/An Ratio" 5.8 6.1 7.4 7.0 12.0 9.8 8.1 6.5 7.3 9.0 9.9 13.0 2.5 3.8 5.7 6.3 6.2 5.6 5.5 5.0 6.0 6.4 9.3 7.0 11.0 8.4 4.6 5.0 5.9 11.0 4.3 7.0 6.0 3.7

7.78 7.78 7.71 7.64 7.63 7.69 7.67 7.52 7.45 7.43 7.42 7.41 7.86 7.77 7.77 7.67 7.64 7.62 7.53 7.42 7.42 7.39 7.49 7.40 7.36 7.30 7.42 7.49 7.48 7.47 7.57 7.32 ~7.26 7.10

The A r / A n ratio is denned as the number of aromatic molecules per anionic unit in the liquid clathrate. The ppm relative to the aromatic resonance in the liquid clathrate. a

6


118

INORGANIC

COMPOUNDS WITH

UNUSUAL PROPERTIES

t h e c l a t h r a t e ; a n d ( c ) t h e l a r g e r the a r o m a t i c m o l e c u l e s , the s m a l l e r the n u m b e r of a r o m a t i c m o l e c u l e s i n the l i q u i d c l a t h r a t e . P o i n t s a a n d c a r e m o s t v i v i d l y d e m o n s t r a t e d i n t h e d a t a f o r the t e t r a a l k y l a m m o n i u m i o d i d e


series d e p i c t e d i n F i g u r e 1.

—ι Methyl

— ι

I n-Propyl

Ethyl

1—

n-Butyl

n-Pentyl

Figure 1. Maximum aromatic/anion ratio liquid clathrates of the form [NfalkytyiHAl^CHJçI]-aromatic. Ο = benzene, X = toluene, and Φ = ethylbenzene. F i g u r e 1 also illustrates one i n t e r e s t i n g a n o m a l y . T h e l a r g e n u m b e r of e t h y l b e n z e n e m o l e c u l e s associated w i t h [ N ( C H n ) ] [ A l ( C H ) c I ] 5

4

2

3

may

s i g n a l the a p p r o a c h of the e n d of l i q u i d c l a t h r a t e b e h a v i o r f o r l a r g e r t e t r a a l k y l a m m o n i u m ions.

O n e c o u l d e x p e c t t h a t f o r the t e t r a h e x y l -

ammonium iodide-ethylbenzene

or the tetrapentylammonium i o d i d e -

p r o p y l b e n z e n e c l a t h r a t e , the a r o m a t i c / a n i o n r a t i o m i g h t b e so great as t o g i v e solutions w i t h n o l i q u i d l a y e r i n g (i.e., t h e y are m i s c i b l e w i t h p u r e solvent). Liquid Clathrates

Based on the Nitrate

Ion

T h e g r o u p of l i q u i d clathrates i n T a b l e I I w h i c h are n o t b a s e d o n h a i l d e - o r p s e u d o h a h d e - c o n t a i n i n g anions differs f r o m the others i n t w o


11.

ATWOOD

w ays.

AND

Liquid

ATWOOD

119

Cfothrates

F i r s t , the a d d i t i o n of the slightest excess of t r i m e t h y l a l u m i n u m

r

( b e y o n d t h e n o r m a l 2:1 s t o i c h i o m e t r y ) changes the c o l o r of the n i t r a t e c o n t a i n i n g l i q u i d c l a t h r a t e f r o m colorless to y e l l o w . P r e s u m a b l y , t h i s is c a u s e d b y s h i f t i n g t h e energy of a n e l e c t r o n i c t r a n s i t i o n b y c o o r d i n a t i o n of the a d d i t i o n a l t r i m e t h y l a l u m i n u m m o l e c u l e . Second,

the

tetraethylammonium

nitrate/tri ( n-propyl ) aluminum

l i q u i d c l a t h r a t e is t h e first c l e a r l y defined l i q u i d c a t h r a t e of a n a l u m i n u m a l k y l other t h a n t r i m e t h y l a l u m i n u m . T h e i n a b i l i t y of l o n g e r c h a i n AIR3


to f o r m l i q u i d clathrates was p r e v i o u s l y b e l i e v e d to b e a t t r i b u t a b l e to t h e size r e q u i r e m e n t of t h e a l k y l groups.

T h u s , for R

is i n a l l p r o b a b i l i t y m u c h greater t h a n 90° (see or Γ

complexes,

- C H , the angle a 3

S t r u c t u r e 2) for C l " , B r " ,

w h i l e the essential a n g u l a r g e o m e t r y

d e s t r o y e d for t h e p s e u d o h a l i d e complexes

could w e l l be

( S t r u c t u r e 9 ). F o r the n i t r a t e

i o n , h o w e v e r , the steric r e q u i r e m e n t s are m u c h less severe (see 10),

Structure

a n d the necessary shape of the a n i o n is p r e s e r v e d . R A1

AIRs

3

RsAl

\

Ν N=N=N—AIR3 θ

Ο 10

9

Reactions of Liquid

Clathrates

T h e i s o l a t e d l i q u i d c l a t h r a t e undergoes t w o possible reactions

(Re

actions 4 a n d 5 ) . M [ A 1 ( C H ) X ] w i t h M = t e t r a a l k y l a m m o n i u m i o n is 2

3

6

M[Al (CH )eX] + 2

M [ A 1 ( C H ) X ] · η aromatic 2

3

M[Al(CHs)»X] + a l i q u i d for a l l c o m p o u n d s

η aromatic

(4)

η aromatic

(5)

τ±

6

for these substances.

3

A1(CH ) 3

3

+

r e p o r t e d so f a r . R e a c t i o n 4 is u n i m p o r t a n t

All M[A1(CH ) X] 3

3

compounds

are solids.

All

K [ A 1 ( C H ) N ] · η a r o m a t i c systems are u n s t a b l e w i t h respect to c o n 2

3

6

3

v e r s i o n b y R e a c t i o n 4 at r o o m t e m p e r a t u r e , as are t h e K [ A 1 ( C H ) N 0 ] · 2

3

η a r o m a t i c a n d the C s [ A l ( C H ) N 0 ] · η a r o m a t i c systems. 2

3

6

3

6

3

O n the

other h a n d , C s [ A l ( C H ) N ] · η a r o m a t i c undergoes R e a c t i o n 5 s p o n 2

t a n e o u s l y (22).

3

6

3

T h e n a t u r e of the a r o m a t i c g r o u p is also i m p o r t a n t ; f o r

example, [ N ( C H ) ] [ A 1 ( C H ) I ] 3

4

2

3

6

c a n n o t b e p r o d u c e d i n the presence

of e t h y l b e n z e n e at r o o m t e m p e r a t u r e because of R e a c t i o n 5.

Therefore,

just as the f o r m a t i o n of M [ A l R X ] is g o v e r n e d p r e d o m i n a n t l y b y a series 2

e


120

INORGANIC

COMPOUNDS WITH UNUSUAL

of lattice e n e r g y considerations (13),

PROPERTIES

so also is the s t a b i l i t y of

M[A1 2

( C H ) X ] · η aromatic. 3

e

T h e r e are a f e w reactions of l i q u i d clathrates w h i c h are b a s e d o n the d e c o m p o s i t i o n of M [ A l ( C H 2

system (23)

) X ] . T h e most t h o r o u g h l y i n v e s t i g a t e d

3

6

i n v o l v e s t h e t h e r m o l y s i s or p h o t o l y s i s of M [ A l ( C H ) N ] 2

3

e

3

(Reaction 6). 180°C M[Al (CH ) N,] 2

3

> M[A1(CH,) 1 +

e

N A1(CH )

4

3

3

(6)

2


3000 A A p a r t i c u l a r l y i m p o r t a n t series of reactions c u r r e n t l y u n d e r i n v e s t i g a t i o n is the s u b s t i t u t i o n of f o r e i g n m o l e c u l e s rate.

i n t o the l i q u i d

clath

F o r e x a m p l e , the m a x i m u m a r o m a t i c / a n i o n b e n z e n e c l a t h r a t e of

[N(CH ) ][Al (CH ) I]—[(CH ) ][A1 (CH ) I] 3

4

2

3

e

3

4

2

3

6

· 6.4C H —substi 6

G

tutes toluene s l o w l y ( w h e n p l a c e d i n contact w i t h toluene ) at r o o m t e m p e r a t u r e . T h e rate is s u c h that, after t w o h o u r s , t h e c o m p o s i t i o n of the c l a t h r a t e is [ N ( C H ) ] [ A 1 ( C H ) I ] · 5 . 4 C H 3

4

2

3

6

6

6

· 0.7C H CH . 6

5

If, h o w

3

ever, the b e n z e n e l i q u i d c l a t h r a t e is h e a t e d w i t h t o l u e n e i n a sealed t u b e at 80 ° C for 24 hours, the c o m p o s i t i o n of the c l a t h r a t e appears to d i r e c t l y p r o p o r t i o n a l to the b e n z e n e / t o l u e n e

( F o r the s o l u t i o n r e f e r r e d to a b o v e , the c o m p o s i t i o n w a s [A1 (CH ) I] · 2.2C H 2

3

6

6

6

be

r a t i o i n the sealed t u b e . [N(CH ) ]3

4

· 3.7C H CH . ) 6

r )

3

It is also p o s s i b l e to substitute n o n - a r o m a t i c m o l e c u l e s i n t o t h e l i q u i d clathrates. So far w e h a v e s t u d i e d t r i m e t h y l a l u m i n u m , c y c l o h e x a n e , a n d ferrocene. A l t h o u g h the details of these experiments are not yet a v a i l a b l e , t h e g e n e r a l t r e n d is a l i m i t e d s u b s t i t u t i o n of the f o r e i g n m o l e c u l e s

to

gether w i t h the e x p u l s i o n of a r e l a t e d v o l u m e of a r o m a t i c m o l e c u l e s .

It

s h o u l d b e n o t e d t h a t i n a l l cases the l i q u i d c l a t h r a t e is i m m i s c i b l e w i t h t h e substituent, b u t exchange

c a n be effected

either t h e r m a l l y o r

by

mechanical agitation. IR Spectroscopic Studies of Liquid

Clathrates

B e n z e n e - c o n t a i n i n g l i q u i d clathrates w e r e chosen f o r these studies b e c a u s e of t h e i r h i g h s y m m e t r y a n d t h e s i m p l i c i t y of the I R s p e c t r u m . T h e b e n z e n e p o r t i o n s of t h e spectra of a l l l i q u i d clathrates w e r e q u i t e s i m i l a r , b u t there w e r e t w o significant differences b e n z e n e a n d the neat b e n z e n e (24):

between

the

guest

the c o m b i n a t i o n b a n d s at 1818 a n d

1962 c m " w e r e b r o a d e n e d , a n d a v e r y w e a k p e a k a p p e a r e d at 990 c m " . 1

1

T h e d a t a i n T a b l e I I I r e v e a l t h a t t h e b r o a d e n i n g of the I R b a n d s at 1818 a n d 1962 c m " is a m e a s u r e of the extent of i n t e r a c t i o n of the c a t i o n 1

w i t h the benzene molecules.

T h e smaller R b

+

and C s

+

cations, i n f a c t ,

h a v e a s p l i t t i n g of t h e degenerate m o d e s whereas the l a r g e r a m m o n i u m


11.

ATWOOD

AND

Liquid

ATWOOD

Table III.

121

Clathrates

I R D a t a f o r Selected L i q u i d C l a t h r a t e s Band Width at Half Height, cmr

1

2

3

6

3

6

Cs[Al (CH ) N ]-7.4C H Downloaded by UNIV OF CALIFORNIA SAN DIEGO on April 13, 2016 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/ba-1976-0150.ch011

2

3

6

3

2

e

3

6

e

6

6

i

4

9

4

2

1 1

6

n

3

4

6

e

t

4

2

3

/19601» 11974/ /19601» \1972J 24 25 25 22 18

0.029 0.448 0.065

1

/18161 11836/ /18151» \1833J 28 28 27 25 24

e

IN ( C H , ) ][A1 (CH ) I] · 6 . 5 C H , [N(C,H,)«][Al,(CH,),I].7.3C.H [N(C H ) ][Al (CH ) I].9.7CeH [N(C,H ) ][Al (CH,),I]-11.0CH [N(C H ) ][Al (CH ) I].13.0C H 4

A: at B: at A/B 990 1035 cmr Ratio cmr

1

Rb[Al (CH ) N ]-6.1C H

e

6

e 6

Absorbance

At 1962 cmr

At 1818 cmr

Clathrate

a

1

1

0.036 0.650 0.055 0.011 c 0.014 0.020 0.014

0.245 c 0.271 0.407 0.234

0.045 C 0.052 0.049 0.060

From Ref. 11. Split into distinct peaks with maxima at wave numbers given in brackets. The absorbance at 990 c m " is obscured by a strong absorbance at 995 c m " that is caused by the N(C2H )4 groups. a

b

c

1

6

1

+

ions o n l y b r o a d e n the peaks. W i t h i n the t e t r a a l k y l a m m o n i u m series, t h e t r e n d is also m i r r o r e d , a n d the e x p e c t e d r e d u c t i o n i n b r o a d e n i n g w i t h a n increased a r o m a t i c / a n i o n ratio can be observed for the tetra-n-pentyla m m o n i u m clathrates. T h e I R s p e c t r u m of b e n z e n e has b e e n t h o r o u g h l y s t u d i e d (24). a b s o r p t i o n at 1818 c m ' is a s s i g n e d as a c o m b i n a t i o n of E

+

mentals w h i c h has E ~ s y m m e t r y .

1

1

u

u

The

+ E " funda g

T h e b a n d at 1962 c m " is assigned as

a c o m b i n a t i o n of the f u n d a m e n t a l s of s y m m e t r y E

+

u

b a n d s thus h a v e t h e E * f u n d a m e n t a l i n c o m m o n . u

+ B

2g

= E ~. u

Both

F u r t h e r m o r e , t h e y are

b o t h degenerate a n d c a n b e b r o a d e n e d b y a p a r t i a l l i f t i n g of the d e g e n eracy. T h e Eu f u n d a m e n t a l is s y m m e t r y f o r b i d d e n , a n d i t is n o t o b s e r v e d w h e r e i t w a s p r e d i c t e d , at 9 7 0 - 9 8 5 c m ' , i n t h e neat b e n z e n e 1

spectrum.

H o w e v e r , a v e r y w e a k b a n d w a s o b s e r v e d i n a l l s p e c t r a of the clathrates at 990 c m " . S i n c e i t appears i n s u c h a d i v e r s i t y of samples, i t m u s t b e 1

assigned e i t h e r to the guest b e n z e n e o r to the t r i m e t h y l a l u m i n u m u n i t s . T h e correctness i n a s s i g n i n g this p e a k to the b e n z e n e is reflected b y t h e a b s o r b a n c e ratios w i t h the p e a k at 1035 c m " Eu

f u n d a m e n t a l of b e n z e n e )

(24).

1

( w h i c h is assigned to the

T h e s e ratios (see

Table III)

are

almost i d e n t i c a l for w i d e l y v a r y i n g m o l e ratios of b e n z e n e a n d t r i m e t h y l aluminum. T h e Eu m o d e is i l l u s t r a t e d as:

_j_

ο

ο +


122

INORGANIC

COMPOUNDS WITH

UNUSUAL

PROPERTIES

T h e fact that this is the o n l y m o d e affected b y the f o r m a t i o n of t h e l i q u i d c l a t h r a t e indicates t h a t the i n t e r a c t i o n is l o c a l i z e d o v e r the c a r b o n - c a r b o n b o n d s r a t h e r t h a n b e i n g s y m m e t r i c a l l y c e n t e r e d i n t h e π system. Solid State Clues to Liquid

Clathrate

Behavior

T e m p e r a t u r e is a l l i m p o r t a n t to the existence of l i q u i d clathrates. K [ A 1 ( C H ) N ] · b e n z e n e is r e a s o n a b l y stable ( R e a c t i o n 4 ) 2

3

6

ingly unstable


at 2 5 ° C

3

a n d c o m p l e t e l y stable at 4 0 ° C . (Reaction 4)

C s [ A l o ( C H ) N 0 ] · b e n z e n e is e x c e e d 3

6

3

at 2 5 ° C b u t c o m p l e t e l y

stable at

80°C.

K [ A L ( C H ) N ] · p - x y l e n e does not exist at 25 ° C , b u t i t is stable at 3

130°C.

G

3

I t does not seem u n r e a s o n a b l e that the p r o p e r c o m b i n a t i o n

of

c a t i o n , a n i o n , a n d guest m i g h t f o r m a l i q u i d c l a t h r a t e at s l i g h t l y e l e v a t e d t e m p e r a t u r e s , b u t at r o o m t e m p e r a t u r e it w o u l d f o r m a s o l i d w i t h a s t r u c t u r e s i m i l a r to that of the l i q u i d c l a t h r a t e . W e n o w h a v e w h a t m a y b e a n e x a m p l e of this i n the c r y s t a l s t r u c t u r e of K [ C H S e { A l ( C H ) } ] · 3

3

3

3

2CeH6. The

thermal decomposition

of

the

benzene

liquid

K [ A l ( C H ) S e C N ] p r o d u c e s a n u m b e r of p r o d u c t s 2

3

K[Al (CH,) SeCN] · nC H 2

e

6

3

of We

-*

6

K[CH Se{Al(CH ) } ] 3

clathrate

(Reaction 7).

6

3

3

· 2C H 6

+

6

K[A1 (CH ) CN] + 2

3

6

. . .

(7)

e x a m i n e d the s t r u c t u r e of the m e t h y l s e l e n i d e ; for a n excellent set of x - r a y d a t a , the c o n v e n t i o n a l a g r e e m e n t

i n d e x , R, is 0.092 f o r t h e

{ A 1 ( C H ) } ] p o r t i o n of the m o l e c u l e . 3

3

q u i t e n o r m a l (see

K[CH Se3

A l l b o n d lengths a n d angles are

3

Table I V ) .

Table I V .

Important Bond Lengths and Angles for K[CH Se{Al(CH ) } ] · 2C H 3

Bond

Bond Length, A

Se-All Se-A12 Se-A13 Se-C(m) All-Cll A11-C12 A11-C13

2.596(4) 2.570(4) 2.566(4) 1.93(4) 1.96(2) 2.03(2) 1.98(2)

3

3

3

G

6

Bond

Bond Length, A

Bonds

Bond Angle, °

A12-C21 AI2-C22 A12-C23 A13-C31 A13-C32 A13-C33

2.00(2) 1.96(2) 2.01(2) 1.96(2) 1.99(2) 1.99(2)

Cfm)-Se-All C(m)-Se-A12 C(m)-Se-A13 All-Se-A12 All-Se-A13 A12-Se-A13

104.0(5) 103.9(4) 102.6(5) 115.5(4) 114.5(5) 114.2(4)

T h e a m a z i n g f e a t u r e of the s t r u c t u r e is that, a l t h o u g h t h e R f a c t o r i n d i c a t e s t h a t the p r o b l e m is essentially s o l v e d , t h e b e n z e n e

molecules

( w h i c h c o m p r i s e s o m e 3 5 % of the t o t a l e l e c t r o n d e n s i t y ) h a v e n o t b e e n included.

M o r e o v e r , i t is not possible to l o c a t e a c c u r a t e l y a n d to refine


11.

Liquid

ATWOOD A N D ATWOOD

123

Clathrates

the p o s i t i o n a l p a r a m e t e r s of the b e n z e n e c a r b o n atoms.

I n a l l attempts

to d o so, the t e m p e r a t u r e factors h a v e b l o w n u p ( Β ~ 30 A ) . A l l these 2

observations are c o r r e l a t e d w h e n one realizes t h a t t h e b e n z e n e m o l e c u l e s are b e h a v i n g essentially as a l i q u i d ( t h e r e b y c o n t r i b u t i n g n o t h i n g to t h e b u l k of the x - r a y d a t a ) w h i l e the K [ C H S e { A l ( C H ) 3 } 3 ] u n i t s b e h a v e 3

3

n o r m a l l y a n d d o m i n a t e the x - r a y d i f f r a c t i o n p a t t e r n .

(We

believe

that

h i g h t h e r m a l m o t i o n better accounts for the c r y s t a l l o g r a p h i c d a t a t h a n does d i s o r d e r .

O n a difference

F o u r i e r m a p , v e r y w e a k peaks c a n

be


seen i n g o o d positions for a n o r d e r e d s i x - m e m b e r e d r i n g . )

Figure 2. Unit cell packing diagram for K[CH Se{Al(CH ) } -] · 2C H 3

3 3 3

6

6

C a r e f u l e x a m i n a t i o n of t h e u n i t c e l l p a c k i n g i l l u s t r a t i o n ( F i g u r e 2 ) , t o g e t h e r w i t h c r u d e p l a c e m e n t of the b e n z e n e m o l e c u l e s , affords a m i c r o s c o p i c p i c t u r e of the c r y s t a l l i n e s o l i d i n w h i c h there are l a y e r s of s o l i d m a t e r i a l a l t e r n a t i n g w i t h layers of l i q u i d ( S t r u c t u r e 11 ).

( T h e r e are t w o

e

m vT7

4L· \X7

4L· vU

4L· vx/

4L· \js

sj?

Λ

4L· vi/

vf

Kj?

^\

/τ\ vT7

ST\

4L· vi/

4L· \^

4L· vu

4L· vT

4L· vy

4L· vx/

4L· vj/

4L· vT/

4L· vT7

4L· vx/

4L· vT?

4L· vX»

^\

11


vX7

124

INORGANIC

COMPOUNDS WITH

UNUSUAL

PROPERTIES

c r y s t a l l o g r a p h i c a l l y i n d e p e n d e n t p o t a s s i u m ions i n t h e a s y m m e t r i c u n i t ; one is associated w i t h t h e s o l i d l a y e r , the other w i t h the l i q u i d l a y e r . ) C a r e m u s t b e t a k e n that the t e r m ' l i q u i d " is n o t m i s i n t e r p r e t e d .

The

l a y e r is l i q u i d i n t h a t the t h e r m a l m o t i o n of the b e n z e n e m o l e c u l e s is v e r y h i g h , b u t i t is c e r t a i n l y s o l i d i n t h a t the b e n z e n e m o l e c u l e s h a v e n o t r u e t r a n s l a t i o n f r e e d o m because of the p r e s e n c e of t h e p o t a s s i u m ions

(see


S t r u c t u r e 12 for a top v i e w of six u n i t cells of the l i q u i d l a y e r ) .

4 4 X

X

\ y 12 C a r e f u l i n s p e c t i o n of F i g u r e 2 reveals t h a t t h e s t r u c t u r e is t h a t of a reverse c l a t h r a t e : t h e a r o m a t i c m o l e c u l e s are associated w i t h the o r g a n i c regions of the anions. K [ C H S e { A l ( C H ) 3 } 3 ] * 2 C H 3

6

3

6

m a y w e l l present

l i q u i d c l a t h r a t e f o r m a t i o n at a n e l e v a t e d t e m p e r a t u r e , for the a n i o n does h a v e the p r o p e r shape ( S t r u c t u r e 1 3 ) .

H o w e v e r , this has n o t b e e n v e r i -

A1(CH ) 3

(CH ) A1 3

3

A1(CH,)

J

3

8

I e CH 3

13 fied b e c a u s e of the difficulty i n p r e p a r i n g a p u r e s a m p l e of sufficient size. A t present i t is n o t p o s s i b l e to assess the r e l e v a n c e of solid-state structures to l i q u i d c l a t h r a t e b e h a v i o r , b u t w e f e e l that this is a n i m p o r t a n t area f o r future investigation. Conclusions C o m p o u n d s of the t y p e M [ A 1 ( C H ) X ] r e a c t w i t h s m a l l a r o m a t i c 2

3

6

m o l e c u l e s to f o r m n o n s t o i c h i o m e t r i c l i q u i d c o m p l e x e s for those cases i n w h i c h the a n i o n s t r u c t u r e has b o t h a s e p a r a t i o n of o r g a n i c a n d i n o r g a n i c areas a n d a n a p p r e c i a b l e d i p o l e m o m e n t . the

anion

of

a

substance

which

F o r e x a m p l e , the s t r u c t u r e of

exhibits

this

type

of

behavior,

K [ A 1 ( C H ) N ] ( 1 0 ) , was f o u n d to b e : 2

3

6

3


11.

Liquid

ATWOOD A N D ATWOOD

Y/V Al

125

Chthrates

\/

Al

\ /

II


Ν T h e h q u i d c o m p l e x e s h a v e m a n y of t h e p r o p e r t i e s a s c r i b e d to compounds,

enclosure

a n d t h e t e r m l i q u i d c l a t h r a t e seems to b e a n a p p r o p r i a t e

designation. S i n c e t h e I R s p e c t r u m of the guest b e n z e n e is o n l y s l i g h t l y p e r t u r b e d f r o m t h a t of neat b e n z e n e ,

the a r o m a t i c m o l e c u l e s

must interact only

w e a k l y w i t h the cations i n t h e h q u i d clathrate. T h e s t r u c t u r e of the l i q u i d c l a t h r a t e m a y r e a s o n a b l y consist of e i t h e r r o u g h l y s p h e r i c a l or l a y e r - l i k e d o m a i n s . T h e s e alternatives m a y b e r e p r e sented i n t w o d i m e n s i o n s as Structures 14 a n d 15 r e s p e c t i v e l y . A t present,

14

15

f r o m a c o n s i d e r a t i o n of the p r o p e r t i e s of a r a n g e of h q u i d clathrates, i t is b e l i e v e d t h a t the l a y e r - l i k e s t r u c t u r e ( S t r u c t u r e 1 5 ) is the m o r e l i k e l y . A reverse l a y e r e d solid-state s t r u c t u r e is s h o w n f o r K [ C H S e [ A l ( C H ) 3 } 3 ] 3

3

• 2CeHe. Experimental P r e p a r a t i o n s . T h e t w o different w a y s b y w h i c h t h e l i q u i d clathrates m a y b e p r e p a r e d are best i l l u s t r a t e d b y reference to t h e K [ A l ( C H 3 ) N ] c o m p l e x . B y t h e m e t h o d d e s c r i b e d p r e v i o u s l y ( J O ) , 0.010 m o l e A 1 ( C H ) 3 w a s a d d e d to 0.005 m o l e K N i n N a t m o s p h e r e d r y box. T h e m i x t u r e w a s t h e n sealed i n a b o m b t u b e , h e a t e d to 80° C , r e t u r n e d to the d r y b o x , a n d o p e n e d ; a n o t h e r 0.005 m o l e A 1 ( C H ) w a s a d d e d to the p o w d e r e d contents. A f t e r t h r e e cycles of g r i n d i n g , a d d i n g A 1 ( C H ) 3 , a n d h e a t i n g , 2

e

3

3

3

2

3

3

3


126

INORGANIC

COMPOUNDS

WITH

UNUSUAL

PROPERTIES

the w h i t e c r y s t a l l i n e p r o d u c t w a s d r i e d u n d e r v a c u u m . A t y p i c a l analysis g a v e : c a l c d for K [ A l o ( C H ) « N ] : A l 23.97, C 31.99, H 8.05; f o u n d : A l 23.16, C 29.21, H 7.20. A d d i t i o n of b e n z e n e ( - 0 . 1 0 m o l e ) f o l l o w e d b y h e a t i n g 1 h r at 6 0 ° C a f f o r d e d the l i q u i d c l a t h r a t e K [ A 1 ( C H ) N ] · 5.8CGH6. A d e c i d e d l y i m p r o v e d m e t h o d for p r o d u c i n g the c o m p o u n d s i n v o l v e s s i m p l y a d d i n g 0.005 m o l e K N a n d 0.010 m o l e A 1 ( C H ) to —0.10 m o l e C H i n the d r y box. A l i q u i d c l a t h r a t e i d e n t i c a l i n c o m p o s i t i o n to the one p r e p a r e d b y the p r e v i o u s m e t h o d w a s o b t a i n e d i n 1 h o u r . A l l h q u i d clathrates r e p o r t e d here w e r e s y n t h e s i z e d this w a y . It s h o u l d be n o t e d that the f o r m a t i o n of the l i q u i d c l a t h r a t e is a v i s u a l l y d r a m a t i c event. A s the r e a c t i o n p r o c e e d s , a s e p a r a t i o n of t w o l i q u i d layers ( l i q u i d c l a t h r a t e a n d excess a r o m a t i c ) b e c o m e s o b v i o u s ; u p o n s h a k i n g , the layers r e s e m b l e o i l a n d w a t e r . A n a l y s i s . T h e l i q u i d clathrates w e r e a n a l y z e d b y t h e i n t e g r a t i o n of N M R spectra recorded on a P e r k i n - E l m e r R 2 0 - B instrument. T h e aro m a t i c s t o i c h i o m e t r i c s i n T a b l e I I are i n most cases t h e average of three p r e p a r a t i o n s a n d i n t e g r a t i o n s ; a r e a l i s t i c s t a n d a r d d e v i a t i o n w o u l d be ± 0 . 2 m o l e c u l e s . T h e c h e m i c a l shifts are a c c u r a t e to better t h a n 0.02 p p m . T h e l i q u i d clathrates, a l t h o u g h w a t e r a n d o x y g e n sensitive, are m u c h less r e a c t i v e t h a n the p u r e p a r e n t o r g a n o m e t a l l i c c o m p o u n d s . N o n e of the azides was f o u n d to present a n e x p l o s i o n h a z a r d . I R D a t a . T h e I R s p e c t r a ( i n the 6 0 0 - 3 0 0 0 c m " r e g i o n ) w e r e t a k e n o n neat samples i n 0.025-mm N a C l cells i n the d o u b l e b e a m m o d e w i t h a i r as reference. T h e s p e c t r a w e r e r u n o n a B e c k m a n I R - 7 i n s t r u m e n t w i t h a scan rate of 80 c m ' V r n i n a n d 25 c m / i n . A l l h a l f - w i d t h d a t a w e r e t a k e n w ith a scale e x p a n s i o n of 10 c m " V i n . at a scan r a t e of 20 c m / r n i n . A l l l i q u i d clathrate spectra were analyzed b y direct comparison w i t h the s p e c t r u m of b e n z e n e t a k e n u n d e r i d e n t i c a l c o n d i t i o n s . X - r a y Diffraction Data. L a t t i c e parameters for K [ C H S e { A l ( C H ) } ] · 2 C « H w e r e d e t e r m i n e d f r o m a least-squares refinement of the a n g u l a r settings of 12 reflections a c c u r a t e l y c e n t e r e d o n a n E n r a f N o n i u s C A D - 4 diffractometer. T h e y are a = 1 0 . 1 4 4 ( 4 ) , b — 1 0 . 1 5 6 ( 4 ) , a n d c = 17.165(6) A , a n d « = 75.90(4), /? = 80.58(4), a n d γ = 60.72(4)°. T h e c r y s t a l system is t r i c l i n i c , a n d the space g r o u p is P I . D a t a w e r e c o l l e c t e d o n the diffractometer b y a c o l l e c t i o n a n d r e d u c t i o n process ( 2 5 ) . 3

3

2

3


6

3

3

6

3

3

6

1

_ 1

r

- 1

3

3

3

3

G

T h e structure was solved b y the Patterson method, a n d refined b y a n i s o t r o p i c least-squares t e c h n i q u e s . F o r 2114 o b s e r v e d reflections, the final R values w e r e : Π

Λ

=

Σ|*Ό| -

\F \ / Σ ^ |

R

2

=

{Sw(|Fo| -

C

0

=

0.086

|F |) /Sw!Fo| } c

2

2

K 2

=

0.092

T a b l e s of p o s i t i o n a l a n d t h e r m a l p a r a m e t e r s a n d of structure f a c t o r a m p l i t u d e s are a v a i l a b l e u p o n request. Acknowledgment W e t h a n k p a s t students S. K . Seale a n d W . R . N e w b e r r y for t h e i r c o n s u l t a t i o n d u r i n g the e a r l y phases of this r e s e a r c h a n d present students


11.

ATWOOD A N D ATWOOD

Liquid

Clathrates

127

R . T . C a r l i n , K . D . C r i s s i n g e r , a n d Κ. E . Stone f o r t h e i r o n - g o i n g efforts i n this area.


Literature Cited 1. Bailey, M. F., Dahl, L. F., Inorg. Chem. (1965) 4, 1299. 2. Ibid. (1965) 4, 1314. 3. Rodesiler, P. F., Griffith, E. A. H., Amma, E. L., J. Am. Chem. Soc. (1972) 94, 761. 4. Kobayashi, Y., Iitaka, Y., Yamazaki, H., Acta Crystallogr. Sect. B (1972) 28, 899. 5. Atwood, J. L., Newberry, W. R., J. Organomet. Chem. (1974) 66, 15. 6. Williams, K.C.,Brown, T. L., J. Am. Chem. Soc. (1966) 88, 5460. 7. Schaschel, E., Day, M.C.,J.Am. Chem. Soc. (1968) 90, 503. 8. Jeffery, Ε. Α., Mole, T., Aust. J. Chem. (1969) 22, 1129. 9. Atwood, J. L., Newberry, W. R., J. Organomet. Chem. (1972) 42, C77. 10. Ibid. (1974) 65, 145. 11. Atwood, J. L., Atwood, J. D., unpublished data. 12. Ziegler, K., Koster, R., Lehmkuhl, H., Reinert, K., Ann. (1960) 629, 33. 13. Lehmkuhl, H., Angew. Chem. Int. Ed. Engl. (1964) 3, 107. 14. Atwood, J. L., Milton, P. Α., Seale, S. K., J. Organomet. Chem. (1971) 28, C29. 15. Weller, F., Wilson, I. L., Dehnicke, K., J. Organomet. Chem. (1971) 30, Cl. 16. Allegra, G., Perego, G., Acta Crystallogr. (1963) 16, 185. 17. Atwood, J. L., Sheppard, W. A. Acta Crystallogr. Sect. B, in press, 1975. 18. Weller, F., Dehnicke, K., J. Organomet. Chem. (1972) 36, 23. 19. Seale, S. K., Atwood, J. L., J. Organomet. Chem. (1974) 73, 27. 20. Atwood, J. L., Bowles, L. K., unpublished data. 21. Weller, F., Dehnicke, K., J. Organomet. Chem. (1972) 35, 237. 22. Atwood, J. L., Newberry, W. R., J. Organomet. Chem. (1975) 87, 1. 23. Atwood, J. L., Hrncir, D. C., J. Organomet. Chem. (1973) 61, 43. 24. Bailey, C. R., Ingold, C. K., Poole, H. G., Wilson, C. L., J. Chem. Soc. (1946) 222. 25. Atwood, J. L., Smith, K. D.,J.Am. Chem. Soc. (1973) 95, 1488. RECEIVED January 24, 1975. Work partially supported by National Science Foundation grant NSF-GP-24852.


Inorganic Compounds with Unusual Properties

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