Optical memories would use organics Scientists at Battelle Memorial Institute's Columbus, Ohio, laboratories are working to perfect an organic "memory plane" that would form the heart of an optical memory system for computers. Their project, headed by chemist Richard A. Nathan and optics expert Carl M. Verber, is part of a National Aeronautics and Space Administration program to develop data storage systems that are more compact and reliable than are currently available electrical and magnetic memory systems. The Battelle approach is based on the fact that some organic materials— stilbene and related compounds, for example—can be changed from the cis to trans configuration (and vice versa) by irradiation with laser light of certain frequencies. The isomers have different indexes of refraction, and the difference can be used to create a phase hologram. The system would work something like this: Blue laser light would be directed through a page composer (an array of 10,000 tiny shutters that are opened or closed as directed by the incoming data signals) onto a l-sq.-mm. area of a 1-mm.-thick film made of the cis isomer. Where the light was not blocked by the shutters, the cis isomer would be changed to the trans isomer; the resulting hologram would contain all the bits of information, corresponding to the arrangement of the page composer. By slightly shifting the angle of the incident laser light between exposures, additional holograms —up to about 100—could be superimposed in the same area. To recover the data, a beam of red laser light (which doesn't trigger the isomeric shift) would be projected at the proper angle through the holographic image onto an array of 10,000 photodiodes that would reconvert the data to electrical signals. Also, the hologram could be erased by irradiating it with green laser light, which changes trans isomer back to cis. Single-crystal inorganic materials such as lithium niobate also are being studied for possible use in optical memories. But Dr. Nathan and Dr. Verber believe that organic materials offer distinct advantages. For one thing, it is relatively easy to make a film of organic material roughly the area of a sheet of typing paper and 1 mm. thick, but extremely difficult to grow a single crystal with the same dimensions. Also, Dr. Nathan notes, it is apparently possible to superimpose no more than six or seven holograms on a given area of the inorganic material, because of the nature of the material itself. In contrast the present maximum of 100 holograms per sq. mm. (for the organic memory plane) is a limitation on the system's optics, not on the material.
The Battelle scientists now are building a prototype device. They estimate that a finished commercial item could be in production in two years, given the demand. They point out that they are working primarily on the memory plane itself; other NASA subcontractors are developing the page composer and other elements of the system.
ENERGY CRISIS SPECIAL Tape Cassettes
Metal atom chemistry scores major gains Unusual zero-valent organometallic compounds have been synthesized by three groups of scientists working independently of one another. Bis(cyclooctadiene)iron has been made at England's Bristol University. From England, too, comes bis(benzene)titanium, made at Oxford University. And tris(butadiene)tungsten and its molybdenum analog were discovered at Pennsylvania State University. As Bristol's Dr. Peter L. Timms puts it, the three events coming in quick succession point to the rapid emergence of metal atom chemistry as a powerful synthetic technique. Apart from the importance of the discoveries from the fundamental chemistry aspect, the new compounds hold promise for industrial chemical applications. They have the potential for strong catalytic activity and might prove useful in olefin polymerizations. Already, Oxford's Dr. Malcolm L. H. Green has shown that bis(arene)titanium compounds catalyze the oligomerization of butadiene rapidly and smoothly. The three groups used the same basic method for making the compounds. Atoms of the metals, generated in a low-pressure environment (about 10~ 4 torr), interact with organic compounds at low temperature. However, specifics of the experimental procedures differ. Dr. Timms and his coworker Dr. Robert Mackenzie at Bristol University, whose work received support from the U.K. Science Research Council, electrically heat a pellet of iron in an alumina-lined molybdenum crucible to about 1500° C. The crucible is at the end of a probe extending into a 2-liter glass flask cooled to -120° C. In the flask is a 10% solution of cyclooctadiene in methylcyclohexane. During the run, the flask rotates in the cooling bath at about 40 r.p.m. As iron atoms are generated, they migrate to the flask wall where they come into contact with the thin film of organic reactant solution. The green-colored bis(cyclooctadiene)iron that is formed dissolves in the methylcyclohexane solvent. At the end of the experiment, Dr. Timms and Dr. Mackenzie add nitrogen or some other inert gas to the flask and purify the product by recrystallization from pen-
Hear Government Experts Discuss: •
Oil supplies
•
Gas supplies
•
Coal supplies
• An audio symposium complete with charts and tables
PLUS
Hear Scientists Discuss: •
Nuclear power-fission & fusion
•
coal gasification
•
desulfurized coal
•
converting wastes to energy
You get 7 cassettes—nearly 5 hours of tape—plus charts and tables for only $35!
Send $35 to ENERGY SPECIAL American Chemical Society 1155 16th Street N.W. Washington, D.C. 20036 Dept. AP
April 29, 1974 C&EN
23
SCIENCE MILESTONES - on TAPE
from c&EN
•
Bristol University's Dr. Timms (left) and Dr. Mackenzie in their laboratory
Vitamin B-12—Total Synthesis Listen to Dr. R. B. Woodward describe his dramatic work
D Vitamin B-12—Biological Aspects International experts discuss biochemistry, biosynthesis, and mechanism of action
-other Science Symposia on Tape also available from ACS—
D The Energy Crisis Outlook for oil, gas, coal • Fuels for the Future—Hydrogen Experts discuss solutions to the energy crisis D Nutrition & Public Policy— Food Quality Govt., industry officials spell it out D Chemical Engineering In Medicine —at the frontier of chemical engineering D Drugs Affecting Learning & Memory A hot topic in drug research D New Solid Waste Disposal Processes New processes set to go commercial • Chemistry of the Moon-I Dr. Urey, top experts reveal findings
ABOVE INCLUDE VISUAL MATERIALS ACS NonMembers members Cassettes only $ 14.00 $ 17.00 10% DISCOUNT if payment accompanies order Name Address Order from: American Chemical Society 1155 16th Street. N.W. Washington, DC. 20036 ATTN: A. Poulos
24
C&EN April 29, 1974
I
tane. The compound, recovered in yields of 60 to 70%, is so reactive that it spontaneously ignites in air. Nuclear magnetic resonance and infrared analyses of bis(cyclooctadiene)iron closely match those of the known corresponding nickel compound. The iron compound is more reactive, Dr. Timms points out, because it has only 16 electrons around the metal whereas the nickel compound has 18. Because of the lower number of electrons involved in the iron derivative, there are open sites for coordination that should make it an interesting candidate as a polymerization catalyst, he says. Dr. Timms hopes that by replacing the cyclooctadiene moiety with phosphine ligands he can prepare a more stable iron complex while retaining the same overall molecular geometry. Such a material, he believes, might play a role similar to that of nickel triethylphosphite, which Du Pont uses in the commercial production of 1,4-hexadiene, a synthetic rubber component, from ethylene and butadiene. At Oxford, Dr. Green and Dennis Young of the inorganic chemistry laboratory use an electron beam gun supplied by G. V. Planer, Ltd., of Sunbury-on-Thames, near London, to vaporize such highly refractory metals as titanium and molybdenum. The technique has led to the discovery of bis(benzene)titanium, which Dr. Green claims is "the first unambiguously classifiable zero-valent titanium organic sandwich compound made to date." It is so highly reactive that it is unlikely that it can be made by the more conventional techniques for making bisarene metal coordination sandwich compounds, Dr. Green believes, since species present in these reaction mixtures would tend to decompose it. Working under a grant from the American Chemical Society-administered Petroleum Research Fund, Dr. Green and Mr. Young use a 5-liter round-bottom glass flask that rotates in a liquid nitrogen cooling bath. At the base of a probe extending into the flask is a water-cooled copper hearth on which a pellet of titanium rests. Pressure within the flask is maintained at about 10~ 4 torr. A stream of electrons emitted when a molybdenum filament is heated by an applied potential between 4 and 5 kv. is directed
onto the titanium, vaporizing it and generating atoms. These atoms travel to the wall of the flask where they interact with a thin film of benzene that is continuously introduced into the flask through a nozzle inlet. The ensuing cocondensation reaction results in the formation of orange-colored bis(benzene)titanium crystals. Since the ligand inlet is well separated from the metal atom source, the cryogenic pumping reduces contact of the ligand vapor with the electron beam gun, which requires a fairly clean environment to work properly. Apart from being "academically interesting compounds," as Dr. Green puts it, bisarenetitanium coordination compounds hold industrial promise because of their highly reactive catalytic ability. Moreover, he finds that it isn't necessary to isolate the compounds. For example, in an extension of the method, he and Mr. Young have replaced the benzene with a dispersion of butadiene in toluene which contains a catalytic quantity of diethylaluminum chloride. When the titanium atoms reach this mixture, there is an almost complete conversion of the butadiene to cis, trans, trans- 1,5,9-cyclooctatriene. This is used as an intermediate in the commercial production of nylon 12. Penn State's Dr. Philip S. Skell, Dr. Edwin M. Van Dam and Dr. Michael P. Silvon have reacted atomic tungsten and molybdenum with butadiene to form zero-valent tris(butadiene)tungsten and tris(butadiene)molybdenum— adducts that, they say, "appear to be unique in the literature of organometallic compounds." Atoms of the metals are produced by passing an electric current through tungsten and molybdenum wires heated to just below their melting points in a high vacuum (about 10~ 4 torr). Cocondensation with the butadiene occurs at liquid nitrogen temperature. Both the tungsten and molybdenum adducts of trisbutadiene are white hexagonal crystals. They are stable in air, which is unusual because most known zero-valent metal compounds are very sensitive to oxidation. The achievement of the Penn State workers is important because of the highly refractory nature of tungsten. It is likely that their method can be extended with equal success to other refractory metals.
