Soluble Silicates - American Chemical Society

19 Tetrabutylammonium H y d r o g e n S i l i c a t e : Synthesis, C h e m i c a l , T h e r m a l , and Crystallographic

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on December 12, 2016 | http://pubs.acs.org Publication Date: June 1, 1982 | doi: 10.1021/bk-1982-0194.ch019

Properties H. GERKE, H. GIES, and F. LIEBAU Mineralogisches Institut der Universität, D-2300 Kiel, Federal Republic of Germany A new crystalline highly acid tetrabutylammonium silicate (1) and several of its derivatives have been synthesized from aqueous solutions. (1) is face-centered cubic with a = 28.605(6)Å, p(exp) = 1.448(5) g cm ; the approximate unit cell content is [N(C H ) ] H [Si O ] · H O. presence of polydentate aminesH N(CH CH NH) Η,n= 1, 2,3 (en, dien, trien) the hydrate water is partly (with en) or completely(with dien and trien) re placed by these amines. The en-containing phase is cubic with a = 28.715(3)Å, p(exp) = 1.446(5) g cm ; the approximate cell content is[N(C H ) ] H [Si O ] ·84HO·36en.Synthesusing [P(C H ) ]OH instead of[N(C H ) ]OHin the presence of en produced the corresponding cubic tetrabutylphosphonium hydrogen silicate. o

-3

144

4

9 4 24

144

168

In

420

the

2

2

2

2

n

-3

o

4

168

420

4

9 4

9 4 24

144

2

4

9 4

Within recent years a fair knowledge of the influence of temperature and in particular of cation properties such as valence, electronegativity and size on the constitution as well as on the conformation of silicate anions has been obtained (\_, 2). For instance, cations of low electronegativity favour topologically linear and highly stretched silicate anions. A decrease of cation valence has a very similar effect. In comparison, the influence of cation size, temperature and pressure on the structure of silicate anions is much weaker. Therefore, in order to study the influence of cation size, it is essential to vary the cation radius as much as possible while keeping the other parameters as constant as possible. Unfortunately, for monovalent monoatomic cations the radius varies only between 0.59& for tetrahedrally coordinated L i and 1.88a for 12-coordinated Cs , for divalent monoatomic cations be+

+

0097-6156/82/0194-0305$06.00/0 © 1982 American Chemical Society Falcone; Soluble Silicates ACS Symposium Series; American Chemical Society: Washington, DC, 1982.

306

SOLUBLE

SILICATES

+

tween 0. f o r 4-coordinated Be^ and 1.61& f o r 12-coordinated Ba (Shannon - P r e w i t t r a d i i ) . In order to i n c r e a s e the range of c a t i o n s i z e i t i s p o s s i b l e to r e p l a c e the monoatomic c a t i o n s by polyatomic i n o r g a n i c com plexes or by organic c a t i o n s . For i n s t a n c e , s i l i c a t e s c o n t a i n i n g 2 +

the r a r e double r i n g anions ^ S i ^ O ,

[

£ ig 2o[P s

0

an(

*

have been obtained by u s i n g ethylenediamine ( e n ) r "12+ Γ Π2+ Γ "12+ complexes such as I Co ( e n ) ^ J , l N i ( e n ) ^ J and | C u ( e n ) j C 3 , 4^ Si

0 _~]

1 0

9


2

5) or | | N ( C H ) " J 3

+

and [jN(CH -CH OH) "]

4

2

2

4

+

(6, ]_, 8) as c a t i o n s .

To study the i n f l u e n c e of c a t i o n s i z e i n more d e t a i l we s t a r t e d a program to synthesize s i l i c a t e s of organic c a t i o n s . Here we r e p o r t the f i r s t r e s u l t s of these s t u d i e s . Syntheses Tetrabutylammonium hydrogen s i l i c a t e hydrate has been syn t h e s i z e d from aqueous s o l u t i o n s of t e t r a a l k y l o r t h o s i l i c a t e s and tetrabutylammonium hydroxide. In a t y p i c a l experiment S i ( 0 C H ^ ) 4

or Si(OC H,-) 2

i s added at room temperature

4

to a 10 percent aque

ous s o l u t i o n of n-^NiC^H^^JoH under continuous a g i t a t i o n . Hydro l y s i s of the t e t r a a l k y l o r t h o s i l i c a t e according to the equation Si(0R)

4

+ 4 H0 2

—>

Si(0H)

4

+ 4

ROH

leads to a homogeneous s o l u t i o n of s i l i c i c a c i d . Such s o l u t i o n s with a r a t i o S i 0 : £ N R j 0 H of about 3 : 1 are subsequently con centrated i n vacuum a t room temperature by evaporating the a l c o h o l and p a r t of the water w i t h i n a few minutes. From such concen t r a t e d s o l u t i o n s a new phase c r y s t a l l i z e d slowly a f t e r about one week at room temperature and normal pressure. 2

4

Crystallographic properties S i n g l e c r y s t a l s with 0.2 mm maximum diameter have been ob t a i n e d . The o p t i c a l l y i s o t r o p i c c r y s t a l s are terminated by the c r y s t a l forms {.100 J* (cube), {,110;} (rhombdodecahedron), and { . l l l j (octahedron) (Figure 1). Quite o f t e n c r y s t a l s are intergrown and t h e i r faces are convex (Figure 2). The l a t t i c e constant determined from s i n g l e c r y s t a l X-ray diagrams i s a = 28.605(6)S. From the systematic e x t i n c t i o n s of Q

r e f l e c t i o n s a face-centered cubic c e l l i s i n f e r r e d . With a mix ture of bromobenzene and tetradecan the d e n s i t y was found to be -3 1.448(5) g cm . X-ray powder d i f f r a c t i o n data are presented i n Table 1.

Falcone; Soluble Silicates ACS Symposium Series; American Chemical Society: Washington, DC, 1982.


Figure 1.

Single crystals of tetrabutylammonium

hydrogen silicate

hydrate.


o

r

1

>

Η

w

ο w

VO


Figure 2.

Intergrown

crystals of tetrabutylammonium faces.

hydrogen

silicate

hydrate

exhibiting

convex


19.

GERKE

ET AL.


Table I .

Tetrabutylammonium

Silicate

309

X-ray powder d i f f r a c t i o n data of tetrabutylammonium hy drogen s i l i c a t e hydrate ( C u K ^ , \ = 1.541 88).

m

I/I,

hkl

d[S]

I/I,

hkl

14.47

90

200

3.2079

50

840

10.22

85

220

3.0582

20

664

8.322

10

222

3.0079

15

931

7.190

35

400

2.8139

20

10.2.0,

5.859

8

422

2.5355

5

880

4.783

12

600, 442

2.5061

10

11.3.1,

971 882 866

862

4.328

50

622

2.4960

9

10.4.4,

4.137

10

444

2.4597

5

10.6.0,

3.985

7

640

2.4244

2

10.6.2

25

642

2.3890

7

12.0.0,

884

553, 731

2.3037

10

11.5.3,

975

2.2389

2

12.4.2,

886

3.8355

3.7385 100 3.5870

5

800

3.4810

95

820

3.3772

15

822, 660

3.3119

20

751,

3.2903

15

662

10.8.0 2.1925

5

13.1.1, 11.7.1 11.5.5,

555 2.0534

8

993

13.5.1, 11.7.5


S O L U B L E SILICATES

310

The c r y s t a l s are hydrophobic, i n s o l u b l e i n water, acetone, d i e t h y l e t h e r , toluene and trichloromethane, and s o l u b l e i n metha n o l , d i l u t e d a c i d s and bases.


Chemical composition With chemical analyses the t o t a l amount of Si,C,N and H and the oxygen content i n excess of S i 0 ~ have been determined. The atomic r a t i o s observed are presented i n Table I I . They are i n good agreement w i t h atomic r a t i o s c a l c u l a t e d f o r the chemical composi tion [0.5 N ( C H ) " ] 0 · 7 . 1 4 S i 0 4

9

4

2

2

· 8.83 H 0.

(1)

2

Table I I . Comparison between observed atomic r a t i o s and those calculated for 0 . 5 [ N ( C H > j 0 · 7 . 1 4 S i 0 · 8 . 8 3 H 0 (calc. 1) 9

4

and f o r [ N ( C H ) ] 4

9

4

2 4

4

2

2

H ^ S i ^ O ^ ]

excess 0

Si

2

. 144 H 0 (calc. 2 ) 2

C

Ν

Η

observed

7.14

9.33

16

1.053

54.92

calc. 1

7.14

9.33

16

1.000

53.64

calc. 2

7.00

9.50

16

1.000

54.00

The s l i g h t excess observed f o r Ν and Η over those c a l c u l a t e d from chemical composition ( 1 ) i s perhaps due to some replacement of 2 ^ N ( C H ) ^ j by 2 N ( C H > + 2 H + H 0, the t r i b u t y l a m i n e being 4

9

4

+

+

4

9

3

2

formed by decomposition of tetrabutylammonium i o n s . T i t r a t i o n of an aqueous suspension of the m a t e r i a l a g a i n s t O.ln HCl and O.ln NaOH i n d i c a t e s four d i f f e r e n t r e a c t i o n s A, B, C and D (Figure 3 ) . The sharp step i n the t i t r a t i o n curve at = 6 i s due to the n e u t r a l i z a t i o n of the S i - 0 groups that are equiva l e n t to the number o f j^N(C^H^)^J c a t i o n s of the s i l i c a t e . At +

lower Pg values (region A of F i g u r e 3) the s o l i d c r y s t a l s are d i s solved o b v i o u s l y by h y d r o l y s i s of S i - 0 - S i bonds. In the b a s i c r e gion C a c i d hydrogen atoms of the s i l a n o l groups Si-OH r e a c t w i t h OH" i o n s . At s t i l l h i g h e r p^ v a l u e s (region D) S i - O - S i bonds are h y d r o l i z e d by hydroxyl groups. The amount of s i l a n o l groups determined from the amount of base used i n r e g i o n C i s i n agreement w i t h the chemical formula [ • « W j o . M O

H

1.72o[

S i

2° ] ' ' · 5

6

1

3

H

2°>



19.

GERKE ET

AL.

Tetrabutylammonium

Silicate

311

PH

1

2

ml 0.1 n NaOH ml 0,1 n HCl Figure 3. Titration curve for tetrabutylammonium hydrogen silicate hydrate in aqueous suspension. Key: ®, SiOSi + H 0 ±^ SiOH + HOSi; (g) SiO~ + H* ±; SiOH; ©, SiOH + OH' ±^ SiO~ + H 0; and ®, SiOSi + OH' ±; SiO~ + HOSi. 2

2


SOLUBLE SILICATES

312

which i s r e c a l c u l a t e d from the chemical composition (1). Taking i n t o account the l a t t i c e c o n s t a n t s and the d e n s i t y of the c r y s t a l s a c e l l cantent of [N(C H ) ] 4

is

9

calculated.

4

2

4

This

Soluble Silicates - American Chemical Society

Recommend Documents