Family Corner

Welcome to our preschool Family Corner. We publish this site several times per year in order to provide information on a variety of topics of interest to preschool parents. All content is written and maintained by the staff of the Belmont Public School Preschool and represents their experiences and favorite choices for gifts; activities; resources; and fun ideas. Click on the pictures for further information on that topic. Enjoy!
The Toy Shelf Link is a list of recommended preschool toys; games; or books staff found to support motor, sensory, language, and cognitive development in children. The Resources Link is a list of resources compiled by our staff that provide interesting, useful or fun ideas for parents of preschool children.
The Staff Tips Link contains ideas from staff members on how to deal with common seasonal concerns voiced by parents of preschoolers.
Two fun activities for the whole family. Season specific pleasures recommended to promote motor, language and social development in your preschool age child.
The Planes, Trains and Automobile Link contains tips on how to make those long family journeys more enjoyable. To contact us: Belmont Public School Preschool Program Ms. Peg Hamilton, Early Childhood Liaison Winn Brook School, 97 Waterhouse Rd., Belmont, Ma 02478 Telephone: 617-993-5695
The Toy Shelf Link is a good source of ideas for gift. Listed below are our staff choices for fun and educational games, books and toys for the preschoolers on your list. They are separated by developmental focus.
Sensory and Gross Motor Toys
Silly Putty Binney and Smith Koosh Ball Koosh Sit n Spin Playskool Playchute Pacific Play Tents Tent and Tunnel Pacific Play Tents Fun-Ride Scooter Hot Wheels Up and Down Roller Coaster Step 2 Splat Gak Splat Hasbro Floam Rose Art Mini-Trampoline

Constructional Toys

Tinker Toys Hasbro Lincoln Logs Knex Kids Knex Knex Marble Run Galt America Inc. Mega Blocks - Megablocks Large Legos Bristle Blocks 50 Piece Wooden Block Set - Brio Soft and Sturdy Deluxe Blocks Step 2
Games for Fine Motor Coordination
(Perceptual Skills) Perfection Milton Bradley Cootie Milton Bradley Hi Ho! Cheerio! Parker Brothers Sequence for Kids Jax Ltd. Mr. Mouth Milton Bradley Hungry Hungry Hippos Hasbro Twister Milton Bradley Race to the Roof Ravensburger Ice Cream Scoops Fisher Price Melissa and Doug Floor and Wooden Puzzles Ants in the Pants- Milton Bradley Dont Spill the Beans Milton Bradley Dont Break the Ice Milton Bradley Fishin Around Game- Milton Bradley I Spy Memory Game Briar Patch Memory Hasbro 130 Piece Wood Pattern Blocks Melissa and Doug

Fine Motor Coordination

(Prewriting and Bilateral Strengthening) Stacking Cups Shelcore MagnaDoodle Tyco Playdough Fun Factory Playskool Big Ten Bowling Set- STATS Magnetic Alphabet Desk Fun Years Magnetic Numbers and Letters Preskool Lite Brite Cube Hasbro Model Magic Crayola Crayola Trace n Draw Projector Crayola Wood Block Melissa and Doug Deluxe Large Standing Easel Melissa and Doug Lacing Beads in a Box Melissa and Doug
* This list was partially compiled by a prior list developed by Ingrid H. Smith, OTR
Here are just some of the reasons why reading picture books with your preschooler is so important:
Books help to develop rhyming skills, and learning to recognize rhyming words helps children learn to read
Read nursery rhymes or other verses Encourage your child to fill in the last rhyming word of a verse (the pictures can give your child a clue about the rhyming word)
Books help to teach children the meaning of words
Encourage your child to talk about the pictures and the story Try to point out the meanings of words using the pictures You can relate new words to words that your child already knows (such as relating the word huge to the word big) You can also teach your child various concepts including colors, sizes, shapes, quantities, and same versus different
Books help to develop sequencing skills, which is the process for children to begin telling their own stories
As you read the story, encourage your child to talk about each event, even if it is just a word or two You can show how two events are connected in a cause and effect sequence After the story, encourage your child to recall events from the story, use the picture to help

Books help to develop storytelling skills
Encourage your child to tell parts of the story (if it is a familiar book) Help your child to make predictions about what will happen next Ask questions while reading, such as who, where, what, how, and when
Books are also wonderful tools to practice articulation (pronunciation of sounds) as well as develop fluency of speech (smooth and uninterrupted pattern of speaking)
Here are just a few suggestions of picture books for Preschoolers: The Mitten (Jan Brett) Goodnight Moon (Margaret Wise Brown) The Runaway Bunny (Margaret Wise Brown) The Grouchy Ladybug (Eric Carle) The Very Busy Spider (Eric Carle) The Very Hungry Caterpillar (Eric Carle) The Very Noisy Cricket (Eric Carle) Jamberry (Bruce Degen) Hey Diddle Diddle and Other Mother Goose Rhymes (Tomie de Paola books)
The fall and winter seasons Staff Tips focus on three areas of parental concern during these busy days. Helping our children to enjoy large family gatherings; setting and maintaining a stress free bedtime routine; and providing active experiences through the winter months are the challenges we address. Hope we help!
Holidays, celebrations, and family gatherings are wonderful, exciting and stressful times for children. Routine is disrupted, bedtime is often later, children (and parents!) are tired and excited, and frequently feeling overwhelmed. You can help your child to enjoy festive occasions by planning in advance.
Prepare your child for the event a few days ahead of time:
Before the big event: 1. Mark the event on a calendar with a visual symbol and together count off the days. 2. Tell your child the Who-What-Where-How of the event (who will be there, what will happen, where it will take place, and how you will get there). Go over twice a day until the event.
3. Practice social responses so that you and your child are not put in an uncomfortable position under pressure (saying thank you for a gift; giving a hug; waving; saying hi.) Using dolls works really well to practice these routines.
4. If the gathering is at your home and other children will be present, talk to your child in advance about identifying toys that he is willing to share, and the toys he will put away or cover as not available.
The Day of the Gathering:
1. On the day of the event, put out a new toy or game for all the children to share, whether the event is at your home or you are traveling. 2. If you are going to someone elses home, bring a favorite and familiar DVD/video to help give your child a time to calm down or be quiet. 3. Avoid caffeine and high-sugar foods (including soda and fruit juices).
3. Avoid caffeine and high-sugar foods (including soda and fruit juices). 4. Keep to your regular routine as much as is humanly possible before, during, and after an exciting event. 5. Talk to your child ahead of time about a quiet place they can be if things get too noisy or busy. Bring a small bag of familiar books, coloring, or another quiet, soothing activity that your child can do without you to regroup. Try to intervene before a breakdown occurs and provide a quiet time. 6. If you can, take a few moments to step outside with your child, or go to a quiet room with them for hugs, rocking, or talking. This can do a lot to calm their system during the busy gathering, allowing them to tolerate more.

The important word in establishing a happy, calm transition to bed each night is routine. Once a child has experienced this routine many times, each piece of it further prepares and calms him for sleep (think of Pavlovs dog and the bell!). Parents can be ready to put a routine in place by doing the following: Start with the time you would like your child to be in bed with lights out, ready to sleep.
Then time how long it normally takes your child to accomplish each task in getting ready for bed, and subtract this time from bedtime. Add in a 5-10 minute transition signal (5 more minutes of play time. Then it is time for your bath). This will be the time you start the bedtime routine every night. With this strategy, you will avoid rushing your child and therefore getting him excited and less able to calm and go to sleep.
Give a verbal transition warning to your child five or ten minutes before he/she needs to begin getting ready for bed. Get full eye contact and acknowledgement from your child when you do this dont just call in from the other room while he is watching TV and says ok often kids are so absorbed in play or TV that they dont truly process what you say, and so when you come in five minutes later to turn off the TV you may get a strong reaction of outrage from your child to them it may be abrupt.
Many parents find it helpful to make a simple picture schedule for each step of the bedtime process (For example, bath, pajamas, brush teeth, 2 books, kiss, sleep). Pictures can be very powerful because even though your child may understand language well, pictures help him/her internalize the steps and usually take the struggle out of the routine. For example, if your child starts to play after brushing his teeth, you can say Harry, go check your schedule. Whats next? When he says 2 books you can say great job would you like to choose them or do you want me to?.
Give your child many choices within non-choices, as you would have done in the example above. Brushing teeth is not a choice, but which flavor of toothpaste he/she uses that night is a choice, etc.
Avoid exercise within two hours of bedtime. This is often hard for parents who have established a fun, interactive routine of wrestling, jumping etc. when they come home from work or right after dinner. If your child has trouble getting to sleep at an appropriate time at night, it would be better to save the active games for the mornings or weekends, and to substitute them with another quieter activity.
It is very important to continue to offer opportunities for active play and physical development during the cold months. Please find some tips for fun activities for children and adults!
DO Make activity a daily routine Dress for the weather Cover nose and face in the cold Leave cell phone OFF

DONT Exercise 2 hours before bedtime Over plan-remember the backyard! Overdo-several shorter activities are as good as one long bout.
Take a walk outside in the rain or snow and over those puddles or snow banks! Use opposite words like big, little, deep, shallow, wet, dry, cold, warm.
Take a Flashlight Safari through the neighborhood. Make a list of things to find. Be creative!
Encourage and join in snow play. Build snow forts; igloos; snowmen. Go sledding. Use spray bottles filled with colored water to decorate the snow. Let your child help with a kid sized snow shovel.
Encourage independent dressing-it builds self-esteem. You can also provide interesting dress-up clothes for play. Include zippers, snaps, buttons, pullovers. Use lots of different fabrics and sizes. Compare!
Indoor Activities Inside camping with real tents or blankets on tables. Musical chairs Exercise mats and video yoga Dancing Treasure hunts Obstacle Courses
The Planes, Trains, and Automobile Link provides staff tips for those long family trips. If the way to grandmas house involves cruising along in a car, soaring up in the sky or riding the rails, these planning tips will help parents and children to relax and enjoy the trip.
Traveling with children can be exciting as well as stressful for families. You know your own child. Sometimes planning ahead can make the trip smoother and calmer for all. Taking into consideration some tried and true tips may help for smooth sailing, railing or rolling along the road. Packing for your trip can help ease the way.
Use your childs back pack to pack a few small familiar toys and activities that they will enjoy. You will know which bag belongs to each child. Let them be involved in choosing what they bring but you control the amount and size of the collection. Keep a stash of small unfamiliar toys (happy meal toys, etc) with you. Introduce them one at a time as needed. The novelty of a new toy may help ease the time sitting. Ziploc bags are your friend! Use them to pack individual personal care kits that include toothpaste, toothbrush, comb/brush, band-aids, shampoo and soap. Use travel size. They will intrigue your child as well as make it easier to transport. Mark each bag with a name. Larger zip loc bags can be used for snacks, wet/ dirty clothing and snack trash. Bring a small photo brag book with favorite pictures for your child. Kids enjoy pictures. You can use this to preview the people that you are visiting as well as use the brag book for a visual schedule for upcoming events. Post-its and pencils/pens help create instant social stories. They also are fun to stick around the childs travel space without causing damage. Keep to your childs routine, especially sleep/wake cycles. Dont skip naps thinking a child will sleep on the trip. This may backfire with an overtired, irritable child. If traveling at night, complete the night time routine as much as possible. Bath, snack, story, etc. Consider having your child wear their comfortable pajamas and socks. Bring a favorite quilt or blanket and pillow. Preview music that you both can live with. For example, if you like James Taylor, let your child listen to it prior to your trip while traveling in the car. This may become music you both can live with. Dont forget to pack your childs old favorites and just grin and bear it. If your child can handle headphones, use a walkman/ mp3 player. Avoid high sugar and caffeinated drinks and snacks prior to your trip. Encourage your child to drink plenty of water all day. Bring disposable bottles of water and mark with names. Sport top water bottles can control the flow. Be aware of restrictions at airports. This will keep your child from becoming dehydrated. Stick with familiar snacks while on your trip. This is not the time to experiment with the new soy snack treats. A bright fluorescent piece of tape or sticker on the back of your childs coat or matching T shirts can help you easily locate them in a crowd. Keep a picture of your children in your wallet just in case you are separated from them. Allow extra time for your travel and let children get out and stretch and have a small play time out of the seat. Remember that your child is traveling with you. Have adult discussions with your partner when your child is not sharing your space. Sometimes children appear to be asleep, but are not. This will avoid your child misunderstanding information as well as sharing private conversations with people you are visiting. Remember they are kids! Think back to your best memories and worst memories of family travel. Share the funny ones with your child. Expect spills, restlessness and tears. It is all part of a childs day. Traveling

funny ones with your child. Expect spills, restlessness and tears. It is all part of a childs day. Traveling wont change this.
Try to keep yourself calm and this will be picked up by your child. Enjoy and keep it simple!

Happy travels!

The Resources Link is a list of resources compiled by our staff that provide interesting, useful or fun ideas for parents of preschool children. The links below include information on development; a resource for parent workshops on issues facing most families; a collection of activity sites that provide coloring pages; art activities; science and math activities and dot-dot worksheets. Finally, there are links leading to sites selling a variety of preschool materials. This is for information only and should not be considered a recommendation.
Useful Websites for Families of Preschoolers
General Child Development and Medical Issues:
www.cfw.tufts.edu/ (child and family web guide)
Parent Training Opportunities:
http://parentingresourceassociates.org/_wsn/page6.html
Pre-reading, literacy and writing activities:
www.starfall.com www.onemorestory.com www.abcteach.com www.activitypad.com/dot-to-dot-10.html

Sign Language:

ASL Browser Michigan State University: http://commtechlab.msu.edu/Sites/aslweb/browser.htm

Supplies and Materials:

www.difflearn.com www.Lakeshore.com
www.discountschoolsupply.com www.reallygoodstuff.com
The Family Activities chosen are fun for all ages and guaranteed to promote cognitive, motor, language and social development in your preschool age child. Our indoor activity is cooking. What could be better than baking a batch of cookies, smelling their wonderful aroma and then eating them? Step outdoors for our other activity and build a snowman! Dress your snowman in your own unique way. Watch it guard the family house at night. Measure the melting that a warm day brings. What happens to the snowman?
10. 9. 8. 7. 6. 5. 4. 3. 2. 1.

Planning a cooking activity allows your child to make decisions and to see, feel, touch and taste the final product. Gathering materials and ingredients promotes organizational skills Looking over the recipe gives you and your child an opportunity to identify familiar numbers, letters and words. Allowing your child to measure ingredients independently develops eye-hand coordination and fine motor control. Making a mess is half the fun! Mixing ingredients is a great opportunity to discuss changes in color, texture, and form. Stirring is one way your child can experience resistance and deep pressure. Working in the kitchen is a time to discuss general safety awareness. While your dish is cooking talk to your child about the steps you followed and the importance of waiting. Cooking is a functional, life-long skill that has real world implications for your preschooler. Theres nothing better than a home-cooked dish!
Teaching preschoolers to put on outerwear is a great way to promote independence, organization, and sequencing. Walking through snow develops physical endurance and strength. Touching snow is an opportunity for sensory exploration (cold vs. hot, light vs. heavy, smooth vs. rough). Creating round balls of snow is a way to expand your childs knowledge of shapes. Rolling the balls of snow promotes cooperation and teamwork among family members. Helping your child stack snowballs develops eye-hand coordination and problem solving. Giving the snowman a face is an opportunity to talk about the placement of specific facial features, as well as emotions. Choosing items to decorate your snowman allows your children to express themselves artistically. Discussing your work of art, is a chance to revisit the step-by-step process of making a snowman. Talk to your child using first.then.language. Its fun to spend time together as a family!

Perspective

Two-dimensional supramolecular chemistry with molecular Tinkertoys
Josef Michl* and Thomas F. Magnera
Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309-0215
or some time now (15), we have worked on the development of a molecular construction kit, analogous to the childrens Tinkertoy construction set, which permits the assembly of complicated objects from a limited set of rods, connectors, and other simple building elements. The idea is to do civil engineering with individual molecular components ranging in size from a few to several dozen. A somewhat related concept of molecular Lego, based on a different set of structural elements, was proposed (7) and developed (8) independently by Stoddard. Both belong to the wider category of modular chemistry, in which a small number of mid-sized rigid molecular structural elements are combined into complex structures (9). At the start of our project, a very limited selection of types and lengths of straight terminally functionalized molecular rods and connectors was available. We synthesized additional ones based on the oligomers of [1.1.1]propellane ([n]staffanes) (10) and on oligomeric 10-vertex and 12-vertex pcarboranes (11). Other laboratories produced polycubyls (12), oligomers of [2.2.2]propellane (13), additional oligomers of 12-vector carboranes (14), and many rods constructed from the more common pphenylene and acetylene subunits. A combination of several types of such structural elements permits one to achieve an accurate match to a desired rod length. A recent comprehensive review (15) makes it abundantly clear that after a decade of effort, considerable flexibility exists in the choice of molecular rod lengths and properties. After some initial experiments with point (4) connectors, which function by forming bonds from a central atom to the termini of several rods, we turned our attention to star (4) connectors, which function by forming a bond between each of several star arm termini to the terminus of a rod or of another star arm. Various suitable star connectors such as 1,3,5-trisethynylbenzene (16) and hexaethynylbenzene (17) were already known and our laboratory provided a few additional terminally functionalized trigonal (18) and tetragonal (19) structures of this type, as did others. Early on, we were faced with several decisions concerning the nature of the po-
rous objects to be built from our rods and connectors: (i) Should they be free-floating or attached to a surface? (ii) Should they be limited in size (zero-dimensional) or infinitely periodic in two or three dimensions? (iii) If periodic, should they be single giant covalent molecules, or should they be supramoleculari.e., formed from repeated units held together by weak intermolecular interactions? (iv) Most important, toward which purpose should their production be directed? Objective After producing some dumb-bell-shaped objects from our [n]staffanes for fun (20), we soon decided to discontinue work with free-floating structures. Surface-anchored structures, although harder to make and characterize, seemed more intriguing. A beautiful collection of free-floating porous polygonal and polyhedral molecules built from rods and connectors has since resulted from work at other laboratories (2126). Our initial decision concerning the size of the objects to be built was in favor of twodimensionally periodic structures. The engineering of nanoporous three-dimensional crystals from molecular constituents was already underway elsewhere (27) and has since made great strides (28, 29), whereas truly two-dimensional monolayer grids and networks built from molecular rods and connectors were unknown and developing a general method for their controlled production represented a challenge that did not appear to be addressed in any other laboratory. Later, we thought, it would be possible to use epitaxy to go into the third dimension in an aperiodic fashion, by adding several different layers on top of each other in register. The resulting designer solids would be quite distinct from ordinary three-dimensional crystals. We decided to make our two-dimensional structures as sturdy as possible, and given their extreme thinness, the choice of covalent rather than supramolecular structures seemed logical. It carried a significant penalty in that under most common conditions the formation of strong covalent bonds is irreversible. This fact prevents the correction of random errors in the synthesis and generates structures with high defect den-

sity. The two-dimensional synthesis would therefore be limited to the relatively few synthetic methods that form strong covalent bonds reversibly, or else random errors would have to be avoided by supramolecular preorganization of the reacting components performed under reversible conditions. Assuming we could make sturdy twodimensional grids of controlled structure, dimensions, and chemical functionalization, what would they be good for? Following up on earlier ideas (25) we are now concentrating on two options. A simple one is to use the grids as ultrathin separation barriers, more regular and thinner than those that have been described to date (30). A more challenging one is related to our interest in surface-mounted dipolar molecular rotors and propellers (31, 32): the grids could be used as scaffolds for the fabrication of regular planar arrays of interacting dipolar electrical rotors. Such arrays, assembled in a controlled fashion, would be quite interesting. They could be ferroelectric (hexagonal or trigonal grids) or antiferroelectric (square grids) (33), could support slowly propagating waves of rotational excitation (3436), and might exhibit other interesting dielectric and optical properties. General Considerations The way in which we decided to go about producing two-dimensional grids was by linear coupling of arm-ends of star-shaped monomers forced to adhere to a surface with their arms parallel to the surface (4, 5, 37). The coupler is brought by diffusion from a solution contacting the surface. A schematic representation of the intended synthesis is shown in Fig. 1. For this purpose, the arms themselves, or alternatively, tentacles attached to the connector especially for the purpose, have to contain chemical functionalities with a large affinity for a surface,
*To whom reprint requests should be addressed. E-mail: michl@eefus.colorado.edu.

Tinkertoy

is a trademark of Playskool, Inc., Pawtucket, RI, and designates a childrens toy construction set consisting of straight wooden sticks and other simple elements insertable into spool-like connectors. The assembly of triangular trinuclear metal cluster units into polyhedra and stacks has also been referred to as Tinker-Toy construction (6).
PNAS April 16, 2002 vol. 99 no. 8
www.pnas.orgcgidoi10.1073pnas.052016299
Fig. 1. Interfacial synthesis of two-dimensional square (a) and hexagonal (b) grids from star-shaped monomers. The freely oating monomers are rst adsorbed on a surface and then coupled into a grid.

pounds of the pyridine family (41) and those containing sulfur (42) seemed particularly promising as candidates for functionalities that would assure firm chemical bonding of our tentacles to the mercury surface. The use of a metal as one of the phases has other advantages. It facilitates in situ use of grazing incidence spectroscopy, and offers good control of adsorption by adjustment of the surface potential. This could be relevant for the ultimate removal of the grid from the surface on which it was synthesized. Another possibility is to sever the tentacles chemically after they have served their purpose, and we demonstrated this successfully with trigonal connectors adsorbed on gold (18). A Covalent Two-Dimensional Grid The very first cross-shaped monomer tested, the anionic lanthanum sandwich complex of tetrapyridylporphyrin that we prepared for the purpose (ref. 37; Fig. 2), adsorbed firmly on mercury under open circuit conditions and was not removed even by boiling organic solvents, which merely exchanged the counterion. This struck us as fortunate, because under identical conditions, tetrapyridylporphyrin itself did not adsorb firmly. We assumed that the difference is related to the presence of negative charge on the sandwich complex and that at a suitable imposed potential the latter would adsorb firmly as well. We proposed that the strong adsorption might be due to mercury ions binding the connectors and preorganizing them into a continuous network. Because in our apparatus the mercury was in contact with copper, it was also conceivable that the binding ions were copper. It was clear from IR spectra that the porphyrin rings of the
and their adhesion has to be essentially irreversible to avoid three-dimensional cross-linking in solution during the coupling step. Yet, the monomers have to be free to rotate and translate in the surface if they are to organize into a perfect grid. This condition suggested the use of a liquidliquid or airliquid interface. These interfaces also offer the advantages of no lasting imperfections such as steps and dislocations, and no permanent surface structure that would dictate a repeat periodthis was important because we were interested in general synthetic procedures applicable to all rod lengths and connector sizes. An additional advantage of liquidliquid and airliquid interfaces is the promise of permitting grids to be harvested by fishing with a metal grid of the kind used in electron microscopy, in addition to other methods of transfer applicable to both solid and liquid surfaces. Our main concern about using airliquid and, particularly, liquidliquid interfaces was that they are not as sharply defined on atomic scale as solidliquid interfaces, and might permit excessive vertical excursions of the interfacially adsorbed material, which would result in the formation of irregular multilayered three-dimensionally crosslinked structures. Two-dimensional covalent coupling of molecules organized in a LangmuirBlodgett (LB) film at an air water interface had been described and yielded sturdy insoluble films, but no evidence for two-dimensional order was detected (38). We did not want to encumber our monomers with long alkyl chains that might be necessary to force them to stay at an airwater interface. In the end, we decided to use mercury as the subphase and to rely on chemisorption rather than physisorption of the connectors to its well defined surface. Polarographers have investigated the adsorption of organic molecules in the mercurywater interface for many years (39), and firmly adhering monolayers of anions, including organic ones, such as oxalate (40), have been long known. Among uncharged species, comMichl and Magnera

Fig. 2. A quasilinear coupler (a, p-xylylene dibromide), a cross shaped monomer (b, lanthanum sandwich complex of tetrapyridylporphyrin), an idealized structure (c), and an STM image (d) of a square grid.
PNAS April 16, 2002 vol. 99 no. 8 4789

SPECIAL FEATURE

adsorbed lanthanum complex were parallel to the surface, suggesting that the four pyridine rings of the bottom deck of the sandwich acted as tentacles and were adsorbed on the surface, whereas those of the other would be available for linking. Treatment with p-xylylene dibromide as a quasilinear coupling agent yielded a product that still adhered well to mercury (43, 44). IR spectra showed that it contained the p-xylylene units and pyridinium rings as expected, and that the porphyrin rings remained parallel to the surface. For an examination of long-range order, we chose scanning tunneling microscopy (STM). Unfortunately, STM cannot be done in situ on liquid mercury (45, 46), and we decided to transfer the product to highly ordered pyrolytic graphite (HOPG) for imaging. This involved boiling in hydrochloric acid to remove all mercury oxide impurities, casting a very thin film of polystyrene over the surface, transferring the film to an HOPG surface, and dissolving the polystyrene. An examination by atomic force microscopy showed that the bottom surface of the polystyrene film that carried the grid was rough, and the transfer undoubtedly caused folding and mechanical damage. Nevertheless, the images (Fig. 2) revealed a series of product molecules in the form of flakes about nm across and 0.7 nm thick. Each flake was composed of squares of the anticipated size, arranged into a grid that was locally ordered to a surprising degree, although the overall order was poor and there were many defects. Two aspects of the result called for a closer examination. First, the IR spectra of the product were more intense than expected for a monolayer, and we were not

PERSPECTIVE

Fig. 3. Surface areas (a) for tetragonal connectors with ve tentacles (b) on mercuryacetonitrile interface determined from LB isotherms as a function of surface potential.
sure that the STM tip did not image merely the bottom layer of several. The presence of multilayers could be an artifact introduced by the transfer to HOPG, but it could also be an indication of problems with the initial coupling on mercury. A better transfer procedure was needed, and it seemed best to enlarge the size of the product molecules sufficiently to permit fishing with a metal net. Second, the local regularity within the grid was striking, considering that the coupling conditions were irreversible. We felt that this supported the tentative proposal (37) that mercury ions formed by oxidation of the elemental liquid weakly bind to pairs of pyridine nitrogen atoms, preorganizing the cross-shaped connectors into a supramolecular grid before the treatment with p-xylylene dibromide. The pyridine arms in the upper deck appear to be a little too long compared with the NHg2N distance, but a rotation of the upper deck relative to the lower deck should permit the p-xylylene unit to bridge them comfortably. There seemed to be no close precedent to such formation of a metal-ion-bound open grid on mercury, but the formation of compact insoluble layers was well known as mentioned above, and somewhat related metal-ion-bound supramolecular grid formation on a graphite electrode had been proposed (47). Both an increase in the size of the product molecules and an improvement in their regularity required an optimization and anneal-

ing of the supramolecular grid present before the coupling procedure. We therefore postponed further work on the covalent grid and the full publication of our results and decided to first examine the putative metalion-bound supramolecular grids in more detail. Cation-Bonded Supramolecular Two-Dimensional Grids We started by securing the collaboration of an electrochemist from an institution with a long tradition in polarography on mercury electrodes, Lubom Pospil from the Heyr s rovsky Institute in Prague, Czech Republic. The work done so far has used star-shaped molecules with tentacles containing one or more thioether sulfur atoms. Four-armed sandwich complexes of tetraarylcyclobutadienecyclopentadienylcobalt carrying five tentacles on the cyclopentadienyl deck (48; L. Pospil, N. Varaksa, T. F. Magnera, T. s Brotin, B. Noll & J. Michl, unpublished results) and three-armed benzene derivatives with three tentacles at the ends of the arms (N. Varaksa, L. Pospil, Z. Janousek, s B. Gruner, B. Wang, J. Pecka, R. Harrison, B. Noll, and J. Michl, unpublished results, and refs. 49 and 50) were all found to promote the anodic dissolution of mercury at relatively negative potentials, forming chemisorbed surface layers characterized by low electrode capacitance. At somewhat more negative potentials, capacitance in-
creased, suggesting that the solute was then merely physisorbed, and at much more negative potentials, it was the same as in a pure supporting electrolyte, showing no evidence for adsorption at all. Simple thioethers did not form such chemisorbed layers, suggesting that the presence of multiple thioether functionalities in a single molecule indeed led to network formation. As a first step in structural characterization of the chemisorbed layer, we decided to determine the surface area per redox center and per connector molecule. Their mutual relation would provide a convolution of information on the number of redox centers per molecule and on the number of electrons exchanged by each. In perfect monolayer grids, a tetratentacled connector would half-own four metal ions, and a trigonal one, three. Because each ion could exchange one (Hg) or two (Hg2 or Hg2) 2 electrons, two or four electrons could be exchanged per a tetragonal connector, and three halves or three per a trigonal one. A pentatentacled monomer would not be able to form a regular periodic grid, and would perhaps be less likely to use all of its thioether sulfur atoms for metal binding efficiently. Electrochemical techniques gave results that were of the right order of magnitude, but they were not entirely satisfactory because of practical limitations imposed by solubility and related factors. For an independent determination of the mercury surface area per connector molecule under controlled potential conditions at an interface with a liquid electrolyte, we built (50) a trough that modified an LB design developed for work on a mercuryair interface (51) by adding a conducting superphase (acetonitrile with a supporting electrolyte) and by employing the mercury pool as the working electrode in a threeelectrode electrochemical cell. This electrochemical LB trough turned out to be a very valuable tool. LB isotherms were obtained first for two pentatentacled molecules, one whose tentacles were short and contained a single thioether sulfur atom each, and another whose tentacles were long and contained two such sulfur atoms separated by two methylene groups (L. Pospil, N. Varaksa, s T. F. Magnera, T. Brotin, B. Noll & J. Michl, unpublished results). The former formed a firmly chemisorbed surface layer at potentials less negative than that of the mercury redox peak, in agreement with electrochemical capacitance measurements. The surface area per molecule corresponded well to tight packing of the larger of the two decks of the sandwich complex, the tetrasubstituted cyclobutadiene. At more negative potentials, where capacitance measurements suggest mere physisorption, the LB isotherms indicated nearly no resistance to compression, which apparently causes the adsorbed molecules to move into the superMichl and Magnera

4790 www.pnas.orgcgidoi10.1073pnas.052016299
phase. The LB results for the molecule with five tentacles containing two sulfur atoms apiece were more intriguing (Fig. 3). Here, compression met with significant resistance both at potentials less negative and those more negative than the mercury redox peak, but the extrapolated surface area per molecule was much larger (4.5 nm2) in the former region than in the latter (3.3 nm2). Again, this was in agreement with electrochemical data. It suggested first, that the adsorption can remain firm even when the mercury ions are reduced to elemental mercury, and second, that the tentacles then spread much less on the surface, permitting a tight packing of the upper decks. The mental image that we have of these molecules is that of five-legged daddy longlegs spider resting on its belly with legs stretched at less negative potentials and standing up at more negative potentials, but this is yet to be proven. Especially clear-cut results were obtained with trigonal connectors that contained one thioether sulfur atom in each of the three tentacles (N. Varaksa, L. Pospil, Z. Jas nousek, B. Gruner, B. Wang, J. Pecka, R. Harrison, B. Noll, and J. Michl, unpublished results, and refs. 49 and 50). At potentials more positive than 0.05 V, a value located in the rising part of the mercury oxidation wave (0.1 V), electrode capacitance is extraordinarily low and demonstrates the presence of a firmly adsorbed and highly organized surface layer. The LB isotherms measured in this region are potentialindependent and yield an area of about 6.3 nm2 per molecule. At potentials more negative than 0.1 V, where capacitance values correspond to physisorption, the LB isotherms show very little resistance and yield a zero area per moleculei.e., compression easily removes the physisorbed solute into bulk solution. The results of electrochemical measurements show that the bridging mercury cation is Hg2, or less likely Hg2, and 2 not Hg , as initial results indicated (49), n but we are still performing additional experiments. Further in situ characterization of the structure of the chemisorbed supramolecular grid is to be done by grazing incidence IR spectroscopy. Ex situ characterization by transfer to HOPG and STM imaging is presently being attempted. Until these results become available, we cannot feel confident about the structure of the grid. Nevertheless, it is reasonable to ask whether it is possible to propose a structure that is realistic and would fit the area per molecule deduced from the LB isotherms. If we assume a regular hexagonal grid without defects, the observed molecular surface area corresponds to a structure composed of hexagons with an 2.2-nm edge length between centers of benzene rings. This is entirely reasonable for the structure of the connector, considering the flexibility

Michl and Magnera

Fig. 4. Elementary unit of the hexagonal grid structure proposed for a mercuryion connected trigonal connectors chemisorbed on mercury acetonitrile interface.
of the tentacles. Molecular models suggested two likely conformations of the tentacle chain, differing strikingly in the orientation of the SHg2S or SHgHgS link relative to the edge of the hexagon. In one of these, the two are nearly parallel and in the other, nearly perpendicular. Optimization of the two geometries with the AM1 method yielded planar hexagonal structures with edge lengths of 2.7 and 1.9 nm, respectively. Pending further investigation, we propose the latter structure for the observed grid (ref. 50; Fig. 4), and attribute the difference between 2.2 and 1.9 nm to several factors: the uncertainty in the nature of the mercury ion (Hg2 was assumed in the modeling), errors in the modeling, which used a semiempirical Hamiltonian and neglected the presence of the mercury surface and of counterions, and imperfections in the grid, which undoubtedly reduce the density of surface packing. Our original optimism with regard to facile equilibration and annealing of the supramolecular grid simply by keeping the potential near 0.1 V may have been unfounded, because of an unexpected discovery of very remarkable substantial hysteresis in the oxidative formation and reductive removal of the grid. When the adsorbed monolayer is first formed at a potential more positive than 0.05 V and the potential is subsequently swept to more negative values, reduction of the mercury ions is observed at 0.1 V, but the adsorbed layer survives intact until the potential reaches 0.85 V. This is clear both from the capacitance curve and from the LB isotherms, both of which remain entirely unchanged until then. Yet, the monolayer does not form spontaneously from solution at these negative potentials. Its enormous metastability, presumably due to slow hole nucleation, is puzzling, as one would not expect neutral Hg atoms to hold the thioether sulfur atoms of two tentacles together par-
ticularly well. However, it is not entirely unprecedented in that the five-legged spider molecules mentioned above are also chemisorbed even after the mercury ions are reduced. Currently, we are examining connectors whose tentacles contain pyridine rings. We now expect to find that the lanthanum sandwich complex of tetrapyridylporphyrin indeed binds so well to the surface of mercury because it builds a mercury ion bound square grid already at open circuit potential. It is reasonable that the negative charge of this anion would facilitate the oxidation process relative to the electroneutral tetrapyridylporphyrin itself, and the latter will presumably form a similar grid at potentials more positive than that of the open circuit. In general, the hybrid supramolecularcovalent approach to covalent grid formation seems promising, although it will be necessary to adjust the length of the supramolecular grid forming tentacles to conform to that of the covalent grid forming arms separately in each case. For some purposes, the ion-bonded supramolecular grids may be adequate in themselves, particularly if they can be transferred to other surfaces intact. Hydrogen-Bonded Supramolecular Two-Dimensional Grids Along with metal ion coordination, hydrogen bonding is a favorite in the construction of supramolecular structures under reversible conditions. We felt that if we could construct a weakly bound supramolecular grid from connectors and hydrogen-bonding linkers, perhaps the latter could be later exchanged gradually for irreversibly bound covalent ones of a similar size and shape. If this were feasible without ever taking more than a small fraction of the linkers out of the grid, the regular structure might survive intact until the grid is fully covalent. The first question was, can the initial hydrogenbonded two-component supramolecular grids be formed? An examination of the effect of the addition of hydroquinone and 4,4-dihydroxybiphenyl on the LB isotherms of tetrapyridylporphyrin on a waterair interface encouraged us to believe that they perhaps indeed form a regular square grid in which the pyridine arms of neighboring porphyrins are tied together by the dihydroxyarene linkers. When such water surfaces were formed on HOPG and the water was evaporated, STM showed very regular and very large domains of deposit on the HOPG surface (Fig. 5). However, they did not have the expected tetragonal symmetry, and the best structural interpretation that we could offer was that the porphyrins were bound together by hydroquinones as intended, but were arranged in alternating double rows of macrocycles lying flat and standing perPNAS April 16, 2002 vol. 99 no. 8 4791

horizontal (Schafer) transfer from water surface to HOPG, and we are also working with similar grids on a mercurybenzene interface. Perspective We now appear to be tantalizingly close to being able to synthesize both metal-bonded and hydrogen-bonded regular two-dimensional grids of arbitrary and controlled square and hexagonal structure. Once their domain size and defect density are acceptable, we plan to probe their utility in the fabrication of regular surface-mounted arrays of dipolar molecular rotors. We also hope to proceed with efforts to convert these supramolecular structures into regular free-standing covalent grids of potential use as dipolar rotor carriers or separation membranes.
Fig. 5. HOPG. An STM image of a grid formed from tetrapyridylporphyrin and hydroquinone after transfer to
pendicular (52). The orientations in which the double rows ran were presumably dictated by the direction in which the water
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edge withdrew at the end of the evaporation process. We are presently attempting to avoid this distortion by the use of a
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We are grateful to a large number of enthusiastic collaborators, whose names are given in the references quoted. Over the years, our work on molecular Tinkertoys was supported by the National Science Foundation, the Department of Energy, and the U.S. Army Research Office.
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