Materials for Nonlinear Optics - American Chemical Society

Chapter 35

Clathrasils New Materials for Nonlinear Optical Applications Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on September 19, 2013 | http://pubs.acs.org Publication Date: March 11, 1991 | doi: 10.1021/bk-1991-0455.ch035

1,2,3

1,2,3

1,2,4

Hee Κ. Chae , Walter G. Klemperer , David A. Payne , Carlos T. A. Suchicital , Douglas R. Wake , and Scott R. Wilson 1,2,4

2

3

1

2

Beckman Institute for Advanced Science and Technology, Materials Research Laboratory, School of Chemical Sciences, and Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801 3

4

Hydrothermal methods were developed for the growth of large, 3 mm -sized crystals of pyridine dodecasil-3C (Py-D3C) from a pyridine - S i O - H F - H O system at 190°C. The crystals were acentric at ambient temperature and were weak second harmonic generators. Phase transformations were observed by differential scanning calorimetry to commence at 161 and -46 °C on cooling. The crystal structure of the ambient temperature tetragonal or pseudotetragonal 17SiO ·C H N phase was determined using single crystal X-ray diffraction techniques [ a = 13.6620(5) Å, c = 19.5669(7) Å, Ζ = 4, space group I42d -D12]. The domain structure of this phase was studied using optical microscopy, and domain configurations were manipulated by heat treatment. Scanning electron micrographs strongly suggested that the boundaries of these domains were associated with growth twin boundaries. 2

2

2

5

5

2 d

Clathrasils are host/guest complexes comprised of covalent guest molecules entrapped within cages formed by a silica host framework (1, 2). Like all zeolitic materials, clathrasils have enormous potential as advanced optical and electronic materials whose composite character permits synthetic manipulation of both the molecular structure of the guest species and the extended structure of the host framework (3, 4). Like other zeolites, however, clathrasils also suffer severe handicaps as advanced materials due to a reluctance to form large single crystals and a tendency to form stoichiometrically and structurally defective crystals (5 -10). In the course of our investigations of clathrasils as optical and electronic materials, we have discovered that certain clathrasils having the M T N framework structure ( Π -13) are acentric at ambient temperature. They thus are second harmonic generators and possibly useful nonlinear optical materials. We have succeeded in growing large, 3 mm-sized crystals of the clathrasil pyridine dodecasil-3C, 17Si02·C5H5N, and solved the crystal structure of its ambient temperature, tetragonal phase. The availability of large single crystals has also enabled us to study and manipulate domain structures in the tetragonal phase.

0097-6156/91/0455-0528$06.00/0 © 1991 American Chemical Society

In Materials for Nonlinear Optics; Marder, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1991.

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Experimental Section General Analytical Techniques. Elemental analyses were carried out in the University of Illinois School of Chemical Sciences Microanalytical Laboratory. Solid state C and Si N M R spectra were recorded on a General Electric GN-300 W B spectrometer. C and S i NMR chemical shifts were referenced internally to [(CH3)3Si]4Si, TTMS. A Du Pont 1090 thermal analyzer was used for thermal analyses. Hot and cold stage optical microscopy studies used a Leitz 1350 microscope stage. Scanning electron microscopy was carried out in a JEOL JSM35C microscope. Crystal surfaces were coated with sputtered gold prior to examination. Powder X-ray diffraction patterns were acquired on a Rigaku D / M A X diffractometer using CuK radiation. 1 3

2 9

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on September 19, 2013 | http://pubs.acs.org Publication Date: March 11, 1991 | doi: 10.1021/bk-1991-0455.ch035

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α

Starting Materials and Reagents. Fumed silica (Cab-O-Sil, grade EH-5, Cabot Corporation) and aqueous hydrofluoric acid (reagent grade, 49 wt%, Fisher) were used without further purification. Pyridine (reagent grade, Fisher) was dried over sodium hydroxide and freshly distilled prior to use. Fused quartz glass tubing (8 mm ID, 1mm thickness) was purchased from G.M. Associates Incorporated. Preparation of Pyridine Dodecasil-3C. A 2.2 M aqueous H F solution was prepared by dilution of 8.84 mL of 49 wt% H F solution with 108 mL of deionized water. A 1.0 M aqueous pyridinium bifluoride solution was prepared by adding 8.7 mL of pyridine to 100 mL of the 2.2 M HF solution at 0 °C. Fumed silica (90 mg, 1.5xl0" moles) and 0.90 mL ( l . l x l O moles) of pyridine were added to 1.5 mL of the 1.0 M pyridinium bifluoride solution, and the resulting mixture was stirred for 2 h to obtain a p H 6, turbid solution. A 12 cm long fused quartz tube was filled to about 1/3 capacity with this solution, the solution was degassed by three freeze-pump-thaw cycles, and the tube was sealed under vacuum with the solution frozen at liquid nitrogen temperature. The reaction tube was placed in a convection oven at 190 °C for three weeks, during which a considerable amount of the quartz tube was etched away. The tube was then opened, the reaction solution was decanted, and the crystalline product was washed with deionized water and acetone. After air drying for 12 h the Py-D3C crystals were chipped away from the quartz glass wall with an awl to yield 620 mg of product (5.6xl0" moles). Anal. Calcd for I 7 S 1 O 2 C 5 H 5 N : C, 5.46; H , 0.46; N , 1.27; Si, 43.38. Found: C, 5.33; H , 0.62; N , 1.21; Si, 43.36. C C P M A S N M R (TTMS): δ 119.4 (s, meta-C K N), δ 131.3 (s, /?ara-C H N), δ 147.0 (s, ortho-C5H5N). S i C P M A S NMR (TTMS): δ -107.2 (s,Ti), δ -114.3 (s,T ), δ -119.5 (s, T ) , δ -119.9 (s, T3), δ -120.4 (s, T ) . 3

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1 3

5

5

5

5

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2

3

3

Single Crystal X-ray Diffraction Study of Pyridine Dodecasil-3C. Pyridine dodecasil-3C, I 7 S 1 O 2 C 5 H 5 N , crystallized in the tetragonal crystal system with a = 13.6620(5) Å, c = 19.5669(7) Å, V = 3652.2(5) Å and p lc = 2.001 g/cm for Ζ = 4. A transparent, colorless, tabular crystal, sliced from the (1 1 0) face of a large crystal, was bound by the following faces at distances (mm) given from the crystal center: (1 1 0), 0.09; (-1 -1 0), 0.09; (0 1 1), 0.34; (1 0 -1), 0.34; (1 0 1), 0.35; (0 1 -1), 0.35; and (0 0 -1), 0.45. The large crystal volume was required to enable other (nondiffraction) experiments on the same sample. Systematic conditions suggested space group I4jmd οτβ2d; the latter was confirmed by refinement. A total of 4551 diffraction data (2Θ < 70° for +h+k+l: h+k+l = 2n) were measured at 26 °Con a Syntex P 2 i diffractometer using graphite monochromated M o radiation [λ(Κα) = 0.71073 A]. These data were corrected for anomalous dispersion, absorption (maximum and minimum numerical transmission factors, 0.891 and 0.579), Lorentz and polarization effects, and then merged (Ri = 0.027) resulting in 2186 unique data. The structure was solved by direct methods (14); the five silicon atom positions were 3

3

ca


MATERIALS FOR NONLINEAR OPTICS: CHEMICAL PERSPECTIVES

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deduced from an Ε-map. Subsequent difference Fourier syntheses revealed positions for ten oxygen atoms. One of these atoms, O3, was disordered in two positions along the unique 2-fold axis. Anisotropic least-squares refinement (15) of the host molecule using 2132 observed [I < 2.58 σ(Ι)] data converged at R = 0.052 and R = 0.090. Contributions from an "idealized" guest pyridine molecule (no hydrogen atoms) disordered about the Ά symmetry axis within the hexadecahedral cage gave final agreement factors R = 0.039 and R = 0.072. The final difference Fourier map (range 0.70 < e/Â < 0.52) located maximum residual electron density in the vicinity of atom O7. The final analysis of variance between observed and calculated structure factors showed a slight dependence on sine (0). w

w


3

Second Harmonic Generation Measurements. X measurements were carried out with a flashlamp-pumped Y A G laser. Clathrasil crystal grains were segregated by grain size and measured against similarly prepared ground quartz. A photomultiplier tube gated synchronously with the laser detected the second harmonic remaining after filtering of the transmitted beam. 2

Results and Discussion Synthesis and Characterization. Large (3 mm) single crystals of pyridine dodecasil3C (Py-D3C) were obtained by treating fumed silica with an aqueous solution of pyridine and hydrofluoric acid in an evacuated, sealed quartz tube for 500 h at 190 °C. The precise reaction conditions, detailed above in the experimental section, were derived from procedures originally developed by Liebau, Gerke, and Gies (16, 17). The crystals had the truncated octahedral habit shown in Figure 1. Comparison of the X-ray diffraction pattern shown in Figure 2 with published data served to identify the tetragonal M T N structural framwork (7, 10). The formulation HSiC^CsHsN was established by elemental analysis (see above), and chemical homogeneity was evaluated by * C and S i CPMAS N M R spectroscopy (see Figure 3). Analytical data indicated that, within the accuracy of measurement, all hexadecahedral cages in the M T N framework were occupied by pyridine molecules. The C N M R spectrum revealed the presence of only pyridine (18) and no degradation products as guest molecules, and the S i N M R spectrum displayed only resonances assignable to the tetragonal M T N framework (10.19-22). 3

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Phase Transformations. Differential scanning calorimetry of Py-D3C (Figure 4) established the existence of three phases in the -75°C to +200°C temperature range. A transformation from the ambient temperature tetragonal phase to a higher temperature cubic phase (see 10,20) started at +164 °C, with an energy change of 1.6 J/g. The reverse transformation began at +161 °C, with a thermal hysteresis of 8 °C between peak temperatures. Low temperature differential scanning calorimetry showed a lower temperature endothermic transformation from the ambient temperature phase to a low temperature phase commencing at -46 °C, with an energy change of 4.2J/g. The reverse transformation began at -43 °C with a thermal hysteresis of 6 °C between peak temperatures. The phase transformation behavior of Py-D3C was far simpler than that reported for tetrahydrofuran/N2- and tetrahydrofuran/Xe-D3C in reference 10. We attribute this difference in part to impurities in the samples employed, samples that contained methanol and ethylenediamine according to C CPMAS N M R spectroscopy. We have observed that use of Si(OCH3)4 as a silica source or ethylenediamine as a catalyst in clathrasil synthesis introduces defects that can alter phase transition temperatures by as much as 30 °C and/or introduce new phase transformations. 1 3



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Figure 1. Optical micrograph of an as-grown crystal of Py-D3C exhibiting a characteristic truncated octahedral shape. Domains are apparent in transmitted cross-polarized light.


531


Py-D3C


25° C

20

40 ΖΘ (degrees)

1Λ 7.88 12.88 15.16 15.84 18.14 18.38 19.96 22.50 23.70 23.92 25.96 27.26 27.62 28.64 29.26 30.24 33.00 33.48 34.70 35.66 36.84 37.84 38.12 39.38 39.62 40.34

60

I/Id 11.21 6.87 5.84 5.59 4.89 4.82 4.44 3.95 3.75 3.72 3.43 3.27 3.23 3.08 3.05 2.95 2.71 2.67 2.58 2.52 2.44 2.38 2.36 2.29 2.27 2.23

5 17 72 91 20 38 35 47 47 100 46 69 11 9 15 9 5 5 5 12 3 5 9 10 15 9

Figure 2. X-ray powder diffraction pattern of Py-D3C.


ClathrasUs

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Py-D3C 25°C


TTMS

^Ca

ι

HC,

ο

ι

.C H C

Cb

Cc

C

0

1 ι ι ι I ι ι ι I ι ι ι I ι ι ι I ι ι ι I ι ι ι I ι ι ι I ι ι ιJ_LJ.

160

120

80 8( C)

40

0

1 3

Py-D3C ocop

8( Si) 29

1 3

Figure 3. Solid state C (top) and spinning N M R spectra of Py-D3C.

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Si (bottom) cross-polarized magic angle


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2.0,

~L5

1 Py-D3C 2deg/min 29.2 mg

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159°C

I

8.0

ι

I ι I 160 170 Temperature (°C)

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Py-D3C 2deg/min 29.2 mg

^6.0

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σ Χ

-47°C Λ

2.0h Cooling -60

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-43°C

Ε |4.0|

Heating

161°C

Cooling

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/ V 167°C

/ \

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-\

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Λ

ο 1.0

τ

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164°C

I Χ

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7 \J

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Heating

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-41°C

-46°C ι

I ι 1 -50 -40 Temperature (°C)

-30

Figure 4. Differential scanning calorimetry curves for Py-D3C.


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Clathrastts

The phase transformations of Py-D3C were also monitored by N M R spectroscopy. Distinct S i N M R spectra were observed for all three phases as reported in references 10 and 20. H N M R spectra of deuterated Py-D3C samples showed rapid isotropic rotation of the guest molecules in the ambient and high temperature phases but restricted rotation in the low temperature phase. The domain structures of the three Py-D3C phases described above were observed by optical microscopy in cross-polarized light. The photomicrograph of an as-synthesized crystal shown in Figure 1 was taken at ambient temperature. Here, parallel arrays of domains were aligned along the principal axes of the pseudo-cubic crystal and intersected with other domain arrays at 60 angles. When thin sections (see Figure 5) were heated to just above 167 °C, these domains disappeared, but reappeared in their original configurations upon cooling below 159 °C. This "memory effect" could be eliminated, however, by quickly heating the crystal to 700 °C and cooling it to below 159 °C to obtain a new domain configuration. According to thermogravimetric analysis and C NMR spectroscopy, this heat treatment does not involve significant loss of pyridine guest molecules. Cold stage microscopy was used to monitor the low temperature Py-D3C phase transformation. Here again, a memory effect was observed: the parallel domain arrays in the ambient temperature phase were lost upon cooling below -47 °C but returned in their original configurations upon reheating above the transformation temperature. 2 9


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0

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Crystal Structure of Tetragonal Py-D3C. The M T N framework structure Q i ) , also known as the ZSM-39 (12), dodecasil-3C (6.13), CF-4 (7), and holdstite (23) structure, is topologically well-defined and known to contain both pentagonal dodecahedral and hexadecahedral cages. The detailed crystal structure of the ambient temperature phase remains undetermined, however, due to disorder problems. A l l single crystal studies to date have yielded a cubic structure in which averaged oxygen atom positions are determined. Given the large size and high purity of the Py-D3C crystals obtained in the present study, however, it was possible to excise a section from a quadrilateral crystal face (see Figure 1) whose domains were not randomly oriented to yield an averaged, cubic structure. Instead, a tetragonal structure was observed where the unique unit cell axis is oriented along the diagonal of a quadrilateral crystal face, Le,., parallel to one of the three cubic axes of the truncated cuboctahedral crystal. The results of the single crystal X-ray diffraction study described in the Experimental Section are summarized in Table I. The structures obtained for the dodecahedral and hexadecahedral cages are shown in Figures 6a and 6b, respectively, and a cutaway spacefilling view of the pyridine environment is shown in Figure 6c. The hexadecahedral cage showed 5 symmetry, and the pyridine guest molecule was disordered over four symmetry-equivalent locations, only one of which is shown in Figure 6b. The ten unique oxygen atoms converged with temperature factors unusually higher than adjacent silicon atom coefficients. This has been attributed to static or dynamic disorder of the host framework (6) and, in fact, the present structural model resolved two statistically disordered sites for atom O3. In Figure 6, the coordinates of these two sites have been averaged and oxygen atom O3 is marked with an asterisk. Alternatively, these oxygen atom temperature factors may represent a twinned orthorhombic structure such that the tetragonal unit cell is the average of two orthorhombic cells. Crystal Growth Mechanism. In order to further investigate the possibility of crystallographic twinning in Py-D3C, a crystal was isolated during the early stages of its growth and examined by scanning electron microscopy. As shown in Figure 7, the surface of an incompletely developed quadrilateral face is composed of rectangular growth steps oriented normal to the cubic axes of the crystal. Since the orientation of



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Figure 5. Optical micrograph of a thin section of a Py-D3C crystal in crosspolarized light. Regions A-D show in detail the parallel domain arrays. Table I. Atomic Coordinates for Non-Hydrogen Atoms in Crystalline 17Si02-C H N 5

Atom Type Sin SÎT2 SiT3a SiT3b SiT3c

Oi 02 03A 03B

b

C

o o o Oz Og o> 4

5

6

O10

Ni c c

d

2

3

C4 C5

Q> -0.0441

x/a 0.5 0.31931(6) -0.21392(6) -0.01353(6) 0.18446(6) -0.1836(5) -0.1945(4) 0.0 0.0 0.0739(2) -0.1125(2) -0.4113(3) -0.0197(4) -0.2313(2) -0.2596(3) -0.2879(2) 0.0089(19) 0.0382 0.0172 -0.0377 -0.0692 0.5811

a

5

Fractional Coordinates z/c y/b 0.0 0.5 0.09160(3) 0.50859(6) 0.05777(4) 0.68790(6) -0.00438(4) 0.61527(6) 0.05793(4) 0.68522(6) 0.125 0.25 0.125 0.75 -0.0115(7) 0.5 0.0096(8) 0.5 0.6688(2) 0.0344(2) 0.6418(3) 0.0342(2) 0.4618(2) 0.0457(2) 0.6527(4) -0.0805(1) 0.4184(2) 0.0735(2) 0.7551(3) 0.0003(2) 0.0757(2) 0.6022(2) 0.2132(13) 0.5880(30) 0.5032 0.1842 0.4114 0.2106 0.2706 0.4070 0.3020 0.4931 0.2713 2

a

U(eq) 0.0161(6) 0.0137(4) 0.0132(4) 0.0146(4) 0.0140(4) 0.045(3) 0.040(3) 0.027(6) 0.034(6) 0.035(2) 0.039(2) 0.036(2) 0.056(3) 0.039(2) 0.040(2) 0.036(2) 0.092(4)

c

1/3 trace of the U (ij) tensor (Â ). h site "A" occupancy 0.28(1). site "B" occupancy 0.22(1). isotropic group thermal parameter and "ideal" geometry imposed on pyridine. d


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Figure 6. Selected fragments of the tetragonal Py-D3C structure : (a) ball and stick model of the pentagonal dodecahedral cage, (b) ball and stick model of the hexadecahedral cage with a clathrated pyridine molecule, and (c) spacefilling cutaway view of the pyridine guest molecule and its oxygen environment. In (a) and (b), silicon atoms are represented by small filled circles and oxygen atoms by larger open circles, and silicon atoms are labeled by their numerical subscripts (see Table I). In (b), all the atoms in the pyridine molecule are represented by shaded spheres. The sphere radii in (c) are van der Waals radii.


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Figure 7. S E M photomicrographs of a quadrilateral face of a Py-D3C crystal in an early stage of growth. Arrows indicate a growth step.


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these steps matches that of the domains observed by optical microscopy, a simple explanation of the "memory effect" noted above is in hand if the domain boundaries coincide with growth twin boundaries. The existence of orthorhombic growth twins would also support the interpretation of crystallographic disorder in the tetragonal crystal structure as twinning of an orthorhombic structure. Preliminary Property Measurements. Preliminary measurements of second harmonic generating activity on powder samples of Py-D3C, segregated by grain diameter, determined that JC^for the material is 1/85 ± 20% that of quartz. These measurements also indicated a coherence length at least as long as that of quartz. Acknowledgments The authors gratefully acknowledge support from the U.S. Department of Energy, Division of Materials Science, under contract DE-AC02-76ER01198, and central facilities of the Materials Research Laboratory of the University of Illinois, which is supported by the U.S. Department of Energy. We are also grateful to Drs. F. Liebau and H. Gies for helpful advice. Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.

Liebau, F. Structural Chemistry of Silicates: Springer-Verlag: Berlin, 1985; p 159, pp 240-243. Gies, H. Nachr. Chem. Tech. Lab. 1985, 33, 387-391. Ozin, G.A.; Kuperman, Α.; Stein, A. Angew. Chem. Int. Ed. Engl. 1989, 28, 359-376. Stucky, G.D.; Mac Dougall, J.E. Science. 1990, 247, 669-678. Groenen, E.J.J.; Alma, N.C.M.; Bastein, A.G.T.M.; Hays, G.R.; Huis, R.; Kortbeek, A.G.T.G. J. Chem. Soc.. Chem. Commun. 1983, 1360-1362. Gies, H. Z. Kristallogr. 1984, 167, 73-82. Long, Y.; He, H.; Zheng, P.; Wu, G.; Wang, B. J. Inclusion Phen. 1987, 5, 355-362. Dewaele, N.; Vanhaele, Y.; Bodart, P.; Gabelica, Z.; Nagy, J.B. Acta Chim. Hung, 1987, 124, 93-108. Dewaele, N.; Gabelica, Z.; Bodart, P.; Nagy, J.B.; Giordano, G.; Derouane, E.G. Stud. Surf. Sci. Catal. 1988, 37, 65-73. Ripmeester, J.A.; Desando, M.A.; Handa, Y.P.; Tse, J.S. J. Chem. Soc. Chem. Commun. 1988, 608-610. Meier, W.M.; Olson, D.H. Atlas of Zeolite Structure Types: Butterworths: London, 1987; p 104-105. Schlenker, J.L.; Dwyer, F.G.; Jenkins, E.E.; Rohrbaugh, W.J.; Kokotailo, G.T.; Meier, W.M. Nature 1981, 294, 340-342. Gies, H.; Liebau, F.; Gerke, H. Angew. Chem. Int. Ed. Engl. 1982, 21, 206-207. Sheldrick, G.M. In Crystallographic Computing 3 ; Sheldrick, G.M.; Kruger, C.; Goddard, R., Eds.; Oxford University: London, 1985; SHELXS-86, pp 175-189. Sheldrick, G.M. : SHELXS-76, a program for crystal structure determination, University Chemical Laboratory, Cambridge, England, 1976. Gerke, H.; Gies, H.; Liebau, F. Ger. Offen. DE 3 128 988, 1983. Gerke, H.; Gies, H.; Liebau, F. Ger. Offen. DE 3 201 752, 1983. Pugmire, R.J.; Grant, D.M. J. Am. Chem. Soc. 1968, 90, 697-706. Kokotailo, G.T.; Fyfe, C.A.; Gobbi, G.C.; Kennedy, G.J.; DeSchutter, C.T. J. Chem. Soc.. Chem. Commun. 1984, 1208-1210.


540 20. 21. 22. 23.

MATERIALS FOR NONLINEAR OPTICS: CHEMICAL PERSPECTIVES Strobl, H.; Fyfe, C.A.; Kokotailo, G.T.; Pasztor, C.T.; Bibby, D.M. J. Am. Chem. Soc. 1987, 109, 4733-4734. Fyfe, C.A.; Gies, H.; Feng, Y. J. Chem. Soc., Chem. Commun. 1989, 1240-1242. Fyfe, C.A.; Gies, H.; Feng, Y. J. Am. Chem. Soc. 1989, 111, 7702-7707. Smith, J.V.; Blackwell, C.S. Nature 1983, 303, 223-225. July 2, 1990


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