Structure of Water Soluble Silicates with Complex Cations - American

21 Structure of W a t e r Soluble Silicates w i t h C o m p l e x Cations

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YU. I. SMOLIN Institute of Silicate Chemistry of the USSR Acad. Sci., Leningrad, USSR The results of X-ray determinations of the crystal structures of silicates with complex cations are discussed. Watersoluble single crystals of silicates with Ni(en) , Cu(en) , Co(en) , N(CH ) and N(C H ) cations have been studied. It is shown that i n all structures determined the s i l i c a t e anions have the form of double trigonal and tetragonal rings of the [Si O ] , [Si O ] and [Si O (OH) ] -6 compositions. The reasons of s t a b i l i t y of these anions i n aqueous solutions are discussed. 3

2

2

3

3 4

5 4

-6

6

8

18

15

-8

8

20

2

among a small group of silicates that can be obtained from aqueous solutions at room temperature and normal pressure are silicates with complex c a t i ons. Silicates with chelate complexes of transition metals were f i r s t obtained by V. Molchanov and N . P r i khid ko at the Institute of Silicate Chemistry (1^)· Silicates with alkylaramonium cations were praparea i n aqueous solutions by S. G l i x e l l i and T. Krokowski (2) and D. Hoebbel and W. Wieker (3)· ~ The characterization of the structure of these compounds i s of considerable interest for the crystal chemistry of s i l i c a t e s . In most of the s i l i c a t e structures the silicon-oxygen anion i s joined to cations by sufficiently strong bonds. Because of this the size of cation plays the decisive role i n the determination of the structure type due to the great capab i l i t y of the configuration of the silicon-oxygen anion to adapt i t s e l f to cationic polyhedra. These f

0097-6156/82/0194-0329$06.00/0 © 1982 American Chemical Society Falcone; Soluble Silicates ACS Symposium Series; American Chemical Society: Washington, DC, 1982.


330

SOLUBLE

SILICATES

ideas were confirmed by many determinations of the s i l i c a t e structures* In t h e i r s t r u c t u r e the s i l i c a t e s with complex cations represent a rare exception among a great num ber of s i l i c a t e s t r u c t u r e s * The presence of large q u a n t i t i e s of water i n these compounds permits one t o assume that a n i o n i c - c a t i o n i c i n t e r a c t i o n s occur with p a r t i c i p a t i o n of water molecules v i a a system of hyd rogen bonds. I t i s known that water molecules can adapt themselves w e l l to e i t h e r s t r u c t u r a l c o n f i g u r a t i o n therefore i n the compounds studied the s i z e and the form of the c a t i o n cannot influence considerably the geometry of the s i l i c o n - o x y g e n anion* Severe con d i t i o n s determining t h i s geometry i n usual s i l i c a t e s t r u c t u r e s may be s i g n i f i c a n t l y softened here* I t could be expected therefore that the s i l i c o n - o x y g e n r a d i c a l s i n s i l i c a t e s with complex cations possess unusual c o n f i g u r a t i o n . These considerations prompted a study of the s t r u c t u r e of these compounds by methods of X-ray s t r u c t u r a l a n a l y s i s . In recent years s i l i c a t e s with complex cations found a l s o important p r a c t i c a l a p p l i cation. C e l l parameters and i n t e n s i t y data f o r a l l c r y s t a l s were obtained with a counter d i f f r a c t o m e t e r using MkK monochromatic r a d i a t i o n . The s t r u c t u r e s were determined by three-dimensional Patterson and e l e c t r o n d e n s i t y syntheses and r e f i n e d by l e a s t squa res method with i s o t r o p i c temperature f a c t o r s f o r the s i l i c a t e with chelate complexes and with a n i s o t r o p i c temperature f a c t o r s f o r a l l others. Table I shows the compositions and c r y s t a l l o g r a phic data f o r the compounds s t u d i e d . ( I t should be noted that the exact formulae of some of these compo unds were unknown before since using chemical a n a l y s i s only e s t a b l i s h e d that the S i / 0 r a t i o i n these s i l i cates was equal to 2 : 5 ) . The formulae given are based on the X-ray s t r u c t u r a l a n a l y s i s . The c r y s t a l s t r u c t u r e of the s i l i c a t e N i ( e n K was determined using c r y s t a l s obtained during t h e ^ i n t e r a c t i o n of ethylenediamine s o l u t i o n of n i c k e l hyd roxide with a s o l u t i o n of s i l i c a i n ethylenediamine. In a i r the c r y s t a l s weather therefore they must be protected during the experiment. The s t r u c t u r e scheme i s given i n Figure 1 where the Z-coordinates of atoms are shown i n hundred f r a c t i o n s of the p e r i o d . ^ r The s i l i c a t e anion [SigO^c [] has the formal charge 6. I t can be seen from -^Figure 2 that i n the studied s t r u c t u r e corresponding by a n a l y s i s to the

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


2

2

2 P 2

8

Si 0

2 0

2

3

5

4

4

3

8

6

3

2 0

8

1 5

2

2

3

11.13(1) 97.97(8)

13.91(1) 96.12(8)

110.80(9)

15.62(1)

90

20.48(1)

15.62(1)

10.77(1) 106.03(5)

11.06(1) 102.30(8)

17.23(1) 94.66(8)

22.52(2) 99.89(8) 13.36(1) 84.03(8)

88.46(9)

15.98(1)

9.046(5) 90

13.89(1) 72.08(5)

15.185(5) 120

c(A)

119.69(9)

15.56(1)

14.565(5) 94.73(5)

110.30(5)

17.375(5) 90

b(A)

16..375 ( 5 ) 90

Β

«6< >

a (A)

C r y s t a l data

1/n

P1

2

-[si(CH ) ]

1 8

P1

8

8[N(C H ) ]'Si 0 -37H 0

3

(en) ] - S i 0 ( 0 H ) ° l 6 . 4 H 0

2 Q

PT

Ii:C

8

8[N(CH ) ] S i 0 * 6 4 . 8 H 0

2 iJCo

2

1 5

PT

11

8

4 (Ou (en) 1 - S i 0 ·38H 0

3

(en) 3- S i 0 P6

i:E

Space Group

" 26H 0

3 [Ni

Compound

Table I.


7.7

2100

4300 8.6

7.3

4030

1950 7.1

8.9

1990

980 9.2

F(hkl) R %


332 SOLUBLE SILICATES



21.

SMOLIN

Figure

2.

Water

Soluble

Silicates

with

Complex

Silicate anion [Si 0 ]' , the double trigonal permission, from Ref. 4.) 6

ls

6

Cations

ring.

(Reproduced,


with


334

SOLUBLE

SILICATES

formula of d i s i l i c a t e a new form of the s i l i c o n - o x y gen r a d i c a l not described e a r l i e r i s r e a l i z e d , the double t r i g o n a l r i n g s closed up around the t h r e e f o l d a x i s . The s i l i c o n atoms and the common oxygen atoms of the t r i g o n a l r i n g s formed by three s i l i c o n - o x y g e n tetrahedra l i e approximately i n one plane* Two r i n g s share common tops of the tetrahedra and form a double t r i g o n a l r i n g . As each tetrahedron has three common tops and one f r e e top, the Si/0 r a t i o w i l l be equal to 2:5, with the gross formula of the r i n g SigO^c. Figure 3 shows a l s o the chelate complex of ^ Ni (en)-2 which has a gauche-gauche c o n f i g u r a t i o n and Ill-conformation* The cations and the s i l i c a t e anions are attached to each other with a system of hydrogen bonds formed by the water molecules* Each terminal oxygen atom o f the r i n g i s bonded to three water molecules. The che l a t e complex i s included i n the system of hydrogen bonds through the HH -groups (4)· Figure 4 i s a schematic r e p r e s e n t a t i o n of the s t r u c t u r e of the s i l i c a t e s with the copper ethylenediamine complex* I t i s seen that the n u c l e i of che l a t e complexes - copper atoms - occupy p r i v a t e p o s i t i o n s at the centers o f symmetry at the beginning o f the coordinates and at the centers of a l l faces of the u n i t c e l l * The s i l i c a t e anion i s located i n the center of the c e l l and can be b e t t e r seen i n Figure 5* This anion i s composed o f two r i n g s , each b u i l t up of four silicon-oxygen tetrahedra. These two r i n g s share f o u r common tops y i e l d i n g the double tetragonal r i n g . Thus, i f the preceding s t r u c t u r e was found to contain the double t r i g o n a l r i n g , i n the given s t r u c t u r e the silicon-oxygen r a d i c a l i s r e a l i z e d o i n the form o f double tetragonal r i n g u S i 0 3~ . A s i m i l a r r a d i c a l was e a r l i e r described only f o r the s t r u c t u r e of ekanite. The ethylenediamine complexes with atoms comple t i n g the c o o r d i n a t i o n of the complex nucleus to the octahedron are shown i n Figure 6 . The coordination polyhedra of copper atoms have the form o f elongated tetragonal dipyramids. The n i t r o g e n atoms form an almost r e g u l a r square at the bases of the pyramids. The copper-nitrogen distance i s much s h o r t e r than that of the nucleus o f the complex - the tops of the dipyramids. Such a form of the coordination polyhedra of copper atoms can be explained by the p e c u l i a r i t i e s of the e l e c t r o n i c c o n f i g u r a t i o n o f the d i v a l e n t cop per atom and i s described i n many s t r u c t u r e determi nations. The water molecules are j o i n e d i n a three-dimen2

8

2 0


SMOLIN

Water

Soluble

Silicates

with

Complex

Cations


21.


335


336

SOLUBLE SILICATES

Figure 5.

Silicate anion [Si O ]' , the double tetragonal ring. permission, from Ref. 5.) 8

20

8

(Reproduced,


with

Water

Soluble

Silicates

with

Complex

Cations


SMOLIN

Figure 6.

Cu(en)

2

complex.

(Reproduced,

with permission,

from Ref.


5.)

SOLUBLE


338

SILICATES

s i o n a l network by a system of hydrogen bonds which includes the l i g a n d MHp groups and the terminal oxy gen r i n g s (15)· Figure 7 shows the s t r u c t u r e o f Co(en)~ s i l i c a t e . C r y s t a l s of t h i s compound u t i l i z e d f o r X-ray a n a l y s i s were obtained by D. Hoebbel and W. Wieker by the r e a c t i o n o f an aqueous s o l u t i o n of cobalt ethylenedia mine hydroxide with a s o l u t i o n of tetramethylsilane i n methanol ( 6 ) . The hydrogen atoms were a l s o l o c a l i z e d i n t h i s s t r u c t u r e which i s of great s i g n i f i c a n c e here as i t followed from the r e s u l t s obtained that the s i l i c o n oxygen anion, which was f i r s t represented i n the form of double r i n g I l S i 0 Π ~ and two a d d i t i o n a l Co(en)ο complexes wixh the +3 charge, are not compen sated ^ by charges. Figure 8 shows the silicon-oxygen anion which i n the given s t r u c t u r e a l s o c o n s i s t s of two r i n g s , each being b u i l t out o f f o u r s i l i c o n - o x y g e n tetrahedra. These r i n g s are j o i n e d by common tops i n a double t e t ragonal r i n g and hydrogen atoms are bonded to two f r e e oxygen atoms. Thus, the l o c a l i z a t i o n o f hydrogen atoms e s t a b l i s h e d the existence o f the a c i d i c s i l i cate anion S i 0 ( 0 H ) i n the c r y s t a l s t u d i e d . Each such r i n g forms hydrogen bonds with t r a n s l a t i o n a l - e q u i v a l e n t r i n g s along the c-axis thus b u i l d ing up i n f i n i t e columns composed of a c i d r a d i c a l s which are j o i n e d to each other by hydrogen bonds. The chelate complexes and water molecules are located between these columns and connect them both e l e c t r o s t a t i c a l l y and through the system o f hydrogen bonds· The chelate complex i s shown i n Figure 9. As the c r y s t a l i s centrosymmetric, d and 1 forms of op t i c a l l y a c t i v e Co(en)^ are present i n the s t r u c t u r e i n equal amounts. The•'atom o f cobalt i s i n an almost r e g u l a r octahedron composed of n i t r o g e n atoms. Each atom of chelate cycle i s located i n the tetrahedron two tops of which are occupied by the neighbouring atoms of the ethylenediamine r i n g and the two others by the hydrogen atoms. The c r y s t a l s t r u c t u r e of tetramethylammonium s i l i c a t e of the composition 8 Qtf(OH^)/J'Si^Op*64H O was then determined* The c r y s t a l s studied were obtained by D. Hoebbel and W. Wieker by a method i n which c o l l o i d a l s i l i c a was d i s s o l v e d i n an aqueous s o l u t i o n o f tetramethylammonium hydroxide ( 7 ) . The c r y s t a l l i z a t i o n was c a r r i e d out with a slow increase i n s o l u t i o n concentration. The s t r u c t u r e determination was made at a temperature of -100°C. The use of low-temperature d

8

8

1 8

2 0

2

p

u


SMOLIN

Water

Soluble

Silicates

with

Complex

Cations

339

Ï


21.

•5

I -κ»

τ I. Ο

I

•«S* ft* CO ·4ζ

s; ο

.1 I

I



340 SOLUBLE


SILICATES


21.

SMOLIN

Water

Soluble

Silicates

with

Complex

341

Cations

mechanics was necessary here, f i r s t l y , f o r preserva t i o n of the c r y s t a l which e a s i l y evaporates at room temperature and, secondly, f o r the g r e a t e r accuracy of s t r u c t u r e determination at the expense of a de crease of the amplitude of thermal v i b r a t i o n s of the c r y s t a l atoms. I t should be pointed out here that the methyl groups possess a high amplitude of thermal v i b r a t i o n s at room temperature. In Figure 10 the atoms are shown by e l l i p s o i d s of thermal v i b r a t i o n s . In t h i s s t r u c t u r e , l i k e the two above-mentioned s t r u c t u r e s , the s i l i c o n - o x y g e n tetrahedra, each joined by three tops to other t e t r a hedra, form a double tetragonal r i n g S i o 0 which i s b e t t e r seen i n Figure 11. The d i s t r i b u t i o n of cations around the large anion C S i o 0 J ~ should be considered as an i n t e r e s t i n g and S i g n i f i c a n t feature of t h i s s t r u c t u r e . In most inorganic s t r u c t u r e s the cations are a p p r o x i mately equally removed from anions. In a given case s i x of the eight tetramethylammonium groups surround the anion o c t a h e d r a l l y , the n i t r o g e n atom of each of these complexes being located on the s t r a i g h t l i n e passing through the anion center and the center of each t e t r a g o n a l r i n g of the S Î Q 0 group. These s i x tetramethyammonium complexes are j o i n e d d i r e c t l y to the anion thus forming the 6j^(OT-), > S i o 0 group with the formal charge -2. The two other cations are located between these groups and connect them with each other. Figure 12 shows the s t r u c t u r e of tetraethylammonium s i l i c a t e . The c r y s t a l s were obtained from s o l u t i o n prepared by d i s s o l u t i o n of p r e c i p i t a t e d s i l i c a i n an aqueous, approximately unimolar s o l u t i o n of tetraethylammonium hydroxide (8). As seen from Figure 12, the s i l i c o n - o x y g e n radical""is represented here by the double t r i g o n a l r i n g . In Figure 13 t h i s anion with the formal charge -6 i s shown s e p a r a t e l y . Like the s t r u c t u r e of tetramethylammonium s i l i c a t e , f i v e of the s i x cations surround the pentahedral anion and the remaining c a t i o n connects these groups with each other. The water molecules a l s o form here a t h r e e - d i mensional system of hydrogen bonds. I t seems reasonable to assume that s i m i l a r groups can a l s o e x i s t i n s o l u t i o n s of alkylammonium s i l i c a t e s and that such surrounding of the s i l i c a t e anion by complex cations protects i t from being de stroyed by water molecules* Studies of aqueous s o l u t i o n s of these s i l i c a t e s made by Hoebbel and Wieker (£) u s i n g paper chromato graphy show the existence of s i l i c a t e groupings main2 0

8

2 o

2 o

2 o u


SOLUBLE

SILICATES


342

Figure

10.

Projection c-axis.

of the 8[N(CH ) ] · Si O · 64.8H O structure along (Reproduced, with permission, from Ref. 7.) S 4

8

g0

s


the

Water


SMOLIN

Figure 11.

[Si O ]' 8

20

8

Soluble

Silicates

with

Complex

radical in the tetramethylammonium with permission, from Ref. 1.)

Cations

silicate.

(Reproduced,



SOLUBLE


SILICATES

Water

Soluble

Silicates

with

Complex

Cations


SMOLIN


SOLUBLE


346

SILICATES

l y of the same s t r u c t u r e as has been found i n the corresponding c r y s t a l s . T h i s f i n d i n g can be used f o r the synthesis of new compounds. The c r y s t a l s t r u c t u r e of a molecular c r y s t a l obtained from s o l u t i o n of t e t ramethylammonium s i l i c a t e by bonding of t r i m e t h y l s i l y l groups to the s i l i c o n - o x y g e n r a d i c a l s was d e t e r mined by us at a temperature of -110°C. The c r y s t a l s of t h i s compound are i n s o l u b l e i n water, transparent and stable i n a i r . Figure 14 shows the molecule of t h i s compound. As can be seen, i t has a nucleus r e p r e s e n t i n g the double tetragonal r i n g S i 0 p close i n s t r u c t u r e to the s i licon-oxygen r a d i c a l of the primary product - the tetramethylammonium s i l i c a t e . The trimethylammonium groups are bonded to the f r e e tops of the r i n g t e t r a hedra. I t i s obvious that the use of s i l i c a t e r a d i c a l s stable i n s o l u t i o n may serve as a way to the synthe s i s of several new compounds. In t h i s connection of s p e c i a l i n t e r e s t i s the work of E. F l a n i g e n et a l ( 1 0 ) who managed to o b t a i n a new z e o l i t e - t y p e form of s i l i c a under hydrothermal c o n d i t i o n from s o l u t i o n of c o l l o i d a l s i l i c a i n aqueous s o l u t i o n of t e t r a p r o p y l ammonium hydroxide. It can be expected that the use of s i l i c a t e s with complex cations and t h e i r s o l u t i o n s w i l l permit one to obtain i n the nearest future some compounds of great importance f o r chemical technology. 8

0


SMOLIN

Water Soluble Silicates with Complex Cations


21.

Figure 14.

Si O s

u

· [Si(CH,),]

s

molecule.

American Chemlcaf Society Library 1155 16th St. N. w. Falcone; Soluble Washington, 0.Silicates C. 20036 ACS Symposium Series; American Chemical Society: Washington, DC, 1982.

348

SOLUBLE SILICATES

Literature Cited 1. Prikhid'ko, N.E.; Molchanov, V.S. Dokl. Akad. Nauk SSSR 1952, 8 6 , 83-6. 2. Glixelli, S.; Krokowski, T. Roczn. Chem. 1937, 17, 309-16. 3 · Hoebbel, D.; Wieker, W. Z. anorg. allg. Chem.


1971, 384,

J.P.;

43-52.

4 · Smolin, Y u . I . Kristallografiya 1970, 15, 31-7. 5 · Smolin, Yu.I.; Shepelev, Yu.F.; Butikova, I.K. Kristallografiya 1972, 17, 15-21. 6. Smolin, Y u . I . , Shepelev, Y u . F . ; Pomes, R.; Hoebbel, D.; Wieker, W. Kristallografiya 1975, 2 0 , 917-24.

7.

Smolin, Y u . I . ; Shepelev, Yu.F.; Pomes, R.; Hoebbel, D.; Wieker, W. Kristallografiya 1979, 24,

8.

Hoebbel, D.; Garzo, G.; Engelhardt, G.; Ebert, R.; Lippmaa, E . ; A l l a , M. Z. anorg. a l l g . Chem. 1980,

38-44.

465,

15-33.

9. Wieker, W.; Hoebbel, D. Z. anorg. allg. Chem. 1969, 366, 139-51.

10. Flanigen, E.M.; Bennet, J.M.; Grose, R.W.; Cohen, Patton, R . L . ; Kirchner, R.M.; Smith, J.V. Nature 1978, 271, 512-16.

RECEIVED March

14, 1982.


Structure of Water Soluble Silicates with Complex Cations - American

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