Our 100th Paper: Chiral Nematic Prussian Blue Analogs

Prussian blue, Fe₄[Fe(CN)₆]₃· x H₂O, is an iconic chemical that has been used as a pigment in paints for centuries. To a chemist, what might be more interesting than Prussian blue’s colour is its molecular structure. As the archetypal coordination polymer, Prussian blue has an extended network structure composed of metal ions connected through bridging ligands. The resulting structure of Prussian blue resembles a framework you might make out of marshmallows and toothpicks, where the marshmallows are iron centres and the toothpicks are cyanide linkers. (Metal-organic frameworks, like the ones Angela made, are a subset of coordination polymers.)

MOF

Hard templating is a method we also described in our post about Susan’s composite materials. A template is used to host the formation of a material. Once the material is formed and the template is removed, the resulting material has holes where the template used to be. Using templates with structures on the nano- or mesoscale can allow us to make materials with interesting properties.

To see if the synthesis of coordination polymers could be combined with the method of hard templation, Pei-Xi, a PhD student in our group, tried to build Prussian blue or its analogs onto a template before removing the template to obtain mesoporous structured Prussian blue.

With chiral nematic mesoporous silica used as a template, Pei-Xi was able to obtain films of mesoporous Zn/Fe Prussian blue analogs. Although this method did not work for other Prussian blue analogs or Prussian blue itself, this work shows that hard templating coordination polymers is a viable method toward making new materials.

A special note: this is our 100th paper! Congratulations Pei-Xi and Vitor! See here for the full paper.

-Debbie

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Chiral Nematic Porous Germania and Germanium/Carbon Films

Germanium (Ge)-based semiconductors have attracted extensive interest in many applications for optoelectronics, detectors, and energy storage. One of the most important potential applications of the Ge materials is as efficient anode materials for lithium-ion batteries (LIBs). In terms of the efficiency and cost-effectiveness, developing new Ge-based semiconductor thin films with engineered porous nanostructures from sustainable materials is an interesting synthetic route for practical technologies. Recently, we used biopolymeric cellulose nanocrystals (CNCs) prepared from plants to produce a new family of Ge-based semiconductors that are available as freestanding thin films and have special spiral nanoporous structures.

In 2010, our group used CNCs to produce photonic silica films where we simply combined silica precursor with cellulose liquid crystals in water. We obtained mesoporous silica films with a twist after calcining the resulting silica/cellulose composites in air to burn away the cellulose template. These new materials are colorful glasses that are useful for photonic and optical technologies (Nature, 2010, 468, 422). We know that Ge is silicon’s neighbor in periodic table, so the question was could we apply this synthetic procedure for germania materials? We first attempted to combine Ge precursor with CNCs in water, but we always obtained cloudy inhomogeneous composite films as a result of strong hydrolysis and condensation of highly reactive germanium alkoxides in water. This means that germanium is very reactive with water compared to stable silane. Consequently, we found it difficult to control the twisting organization of cellulose liquid crystals in the presence of Ge precursor during the air-drying of water.

Reprinted with permission from {Nanoscale, 2015, DOI: 10.1039/C5NR02520F} Copyright {2015} The Royal Society of Chemistry

Reprinted with permission from {Nanoscale, 2015, DOI: 10.1039/C5NR02520F} Copyright {2015} The Royal Society of Chemistry

To address this issue, we developed a new technique for these Ge-based materials where we primarily used a mixed solvent system of water and organic solvent (e.g., DMF). The presence of the organic solvent in the aqueous suspension of CNCs allowed for flexible control of the slow hydrolysis and condensation of germanium precursors. As a result, we can produce large, crack-free freestanding GeO2/cellulose films with brilliantly iridescent colors after air-drying of the mixed suspension. We subsequently pyrolyzed the GeO2/cellulose composites under different calcination conditions to produce twisted nanoporous semiconductor films of GeO2, GeO2/C, and Ge/C. This work was done by Jing Xu, a visiting Professor at UBC and Thanh, currently a post-doc in our group who determined the structures and helped her prepare the paper.

-Thanh

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Coffee Time!

Coffee Time

Every week, the chemistry department at UBC has coffee time hosted by a different group. Last week was the much-anticipated MacLachlan Group coffee time and we provided a feast of homemade baked goods including Odenwälder blaubeerklechs-kuchen, Japanese mochi “hydrogels”, pineapple upside-down cake, and caramel-topped rice crispy squares made with homemade marshmallows. Here are some highlights.

IMG_20150702_145759IMG_20150702_145737IMG_20150702_145745

IMG_20150702_144702IMG_20150702_145650IMG_20150702_144814IMG_20150702_153616Thank you to our amazing group members for the delicious contributions!

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Constructing Supramolecular Architectures

Remember those construction toys where you have interlocking pieces of nodes and plastic rods that can be put together to form a variety of architectural structures? Metal organic frameworks, or MOFs, are like the chemist’s version of these construction toys with metals acting as the nodes and organic molecules acting like the plastic rods to link the metals. Using these building blocks, large frameworks can be created with properties from both the metallic and organic components of the MOF.

MOF Schematics

Schematics of 2D and 3D metal organic frameworks where the gold balls represent metal nodes and blue balls represent organic linkers.

One important aspect of MOFs is that they are designed to be porous – they should have open spaces throughout the framework so that the properties designed into the framework are accessible. One way to design porous MOFs is to make them with large, rigid organic linkers like triptycene (1) or pentiptycene (2). Angela, a recent PhD graduate from our group, designed new triptycene and pentiptycene-based molecules that were suitable for making MOFs and made zinc-containing MOFs with pentiptycene linkers. Although these new MOFs are not porous, the work shows a promising route to incorporating these bulky molecules into future frameworks.

iptycenes

Check out Angela’s framework structures here and to see some other supramolecular structures our group has made, see our post on Nick and Veronica’s anion-templated macrocycles.

-Debbie

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New Composite Materials towards Natural Gas Vehicles

Like using an ice cube tray to make ice in the shape of the holes of the tray, templating is used in chemistry to make materials with specific shapes defined by the templates. Instead of using ice cube trays, chemists use templates with mesopores, holes or pores that are 2 to 50 nanometers wide. (A human hair is on average about 100 000 nanometers wide!)

mesoCo3O4templating

Reprinted with permission from {ACS Appl. Mater. Interfaces, 2015, 7 (21), pp 11460–11466}. Copyright {2015} American Chemical Society.

KIT-6 is an example of a mesoporous material with pores that can be used to template other materials. Susan, a PhD student in our group, used KIT-6 to template cobalt oxide. After templating cobalt oxide, the KIT-6 was removed, leaving just the cobalt oxide in the shape of the KIT-6 pores. Entirely new composite materials were then made using this mesoporous cobalt oxide by filling the space left behind by removing KIT-6. These new composite materials were used to oxidise methane at low temperature, which is an important advance in using natural gas as a fuel for vehicles.

Learn more about Susan’s composite materials here, and to read about a different type of composite materials we’ve made, check out Hessam’s blog post.

-Debbie

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Shape-Shifting Molecules

Some organic molecules are capable of undergoing tautomerism. In tautomerism, the atoms in a molecule are rearranged to form another molecule with the same formula but with different connections between atoms. These two structures are called tautomeric forms. With certain molecules the conversion between tautomeric forms can be very quick: the molecule can shape shift back and forth many times a second.

tautomers

Recently, we were able to take advantage of this property to make an unusual reaction happen. The red bonds between carbon and hydrogen in structure 1 are normally very hard to break. By switching to the tautomeric structure 2, one of these bonds, shown in blue, becomes much easier to break. We replaced this hydrogen atom with deuterium, an isotope of hydrogen with similar chemical properties, to prove this. Replacing hydrogen atoms in a molecule for deuterium is an important chemical process, but it usually requires catalysts (metal complexes which speed up reactions), high temperatures, or strong acids or bases. Instead, we discovered that we can easily swap hydrogen and deuterium atoms by taking advantage of tautomerization.

This work was done primarily by Hessam, a PhD student in our group, with help from Francesco Lelj who did the calculations.

http://pubs.acs.org/doi/abs/10.1021/acs.joc.5b00539

-Hessam and Debbie

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Supramolecular Structures through O-H···Anion Hydrogen Bonding

Hydrogen bonding is a type of weak bond between molecules can occur when a hydrogen atom is bonded to a strongly electronegative atom, and is attracted to a nearby electronegative atom from another molecule. Even though this attraction forms a relatively weak chemical bond, when there are a lot of hydrogen bonds working together, they can have large effects. For example, hydrogen bonding between water molecules gives water an extremely high surface tension, which allows some insects to walk across the surface of a pond without sinking.

In water, hydrogen atoms are bonded to electronegative oxygen atoms and the hydrogen atoms are attracted to oxygen atoms from other water molecules. The hydrogen atoms in water molecules can also be attracted to other electronegative atoms, like negatively charged atoms, or anions.

Hexahydroxyterphenyl is a molecule that has six hydrogen atoms bonded to oxygen atoms. Like the hydrogen atoms in water, these O-H hydrogen atoms in hexahydroxyterphenyl can bind to negatively charged anions. We have used this special type of hydrogen bonding to form large molecules, linking together hexahydroxyterphenyl molecules and anions through hydrogen bonds to form interesting structures.

chloridemacrocycle

Two hexahydroxyterphenyl molecules linked through hydrogen bonding with chloride anions (green). Reprinted with permission from {Cryst. Growth Des., 2015, 15 (3), pp 1540–1545}. Copyright {2015} American Chemical Society

This work was done by Nick, currently a post-doc in our group, and Veronica, a PhD student who determined the structures. Check out more of their neat structures at http://pubs.acs.org/doi/abs/10.1021/acs.cgd.5b00062.

-Debbie

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