CrystEngComm Blog

In this Editor’s choice post, Professor Nicola Pinna, a member of  the CrystEngComm Editorial Board, talks about his favourite articles published in the journal in recent months. Nicola has chosen the most interesting articles in the area of controlled growth of nanostructured materials.  

Mechanistic analyses of nanoscale transformations are not easily accessible, however this case reported by Hoshyargar and co-workers is an exception as the authors managed to follow the transformation of tungsten oxide nanostructures to WS₂ hollow particles. The starting material was synthesized by my favourite approach: a simple, solvothermal treatment of a tungsten alkoxide in benzyl alcohol, with the well-defined tungsten oxide nanoplatelets being subsequently converted to WS₂ by sulfidization at higher temperature. The growth mechanism was investigated by applying advanced electron microscopy techniques at different stages of the solid state reaction. The final product, the “hollow rectangular WS2 nanoboxes”, was shown to be formed by “a cascade” of topotactic and epitactic processes. What I found the most astonishing was the last step of the mechanism, involving the fusion of the layered WS2 sheets forming almost perfect rectangular boxes with 90° kinks (see figure below).

Unconventional upright layer orientation and considerable enhancement of proton–electron conductivity in Dion–Jacobson perovskite thin films
Tomohiko Nakajima, Kiyoshi Kobayashi, Kentaro Shinodaa and Tetsuo Tsuchiyaa
CrystEngComm, 2014, 16, 4113-4119

Single crystal substrates are generally needed for growth of single-crystalline and highly-oriented oxide thin films. However, such an approach cannot be used in industrial applications for which the growth of highly-oriented oxide thin films should take place on common substrates. In this article, Nakajima et al. show that by pulsed laser-assisted annealing of an oxide precursor thin film that is spin coated from a molecular precursor solution, single crystalline RbCa₂Nb₃O₁₀ layered perovskite thin films can be obtained. The peculiarity of these films is that they show upright layer orientations (see figure below) which may allow for them to be used as membranes for fuel cells due to the potential for high proton conductivity in the interlayer sites. The unusual orientation of the films is possibly connected to oxygen deficiencies near the surface which as caused by the high laser power needed to obtain the upright layer orientation.

Layered titanosilicates for size- and pattern-controlled overgrowth of MFI zeolite
Stanislav Ferdov
CrystEngComm, 2014, DOI: 10.1039/C3CE42644K

There is a need for controlling the growth of zeolites on different substrates which can only be achieved by understanding of the heterostructural interconnections between the support and the zeolite material.  This is particularly relevant for industrial applications such as catalysis. In this work, Stanislav Ferdov reports that plate-like crystals of two titanium silicates can act as interesting substrates for the controlled growth of an MFI-type zeolite. The different arrangement of the SiO₄ tetrahedra and TiO₆ octahedra in the two chosen titanosilicates govern the overgrowth behaviour. In one case, the plate-like crystals of the titanosilicate (20–40 μm) are covered with a monolayer of regularly packed-zeolite crystals (see figure below left). In the second case, the support acts as a single-nucleation site and only isolated and larger crystals of MFI zeolite are observed (see figure below right). Although the possibility for controlling the overgrowth of zeolites has clearly been demonstrated, the opportunity for improvement is huge. It can only be successful, however, if combined with a molecular-scale understanding of the heterostructural interconnections between substrate and zeolite.

Ligand dynamic effect on phase and morphology control of hexagonal NaYF4
Suli Wu, Ye Liu, Jie Changa and Shufen Zhang 
CrystEngComm, 2014, DOI: 10.1039/C4CE00109E

It is well accepted that the adsorption of stabilizing ligands at the surface of nuclei dramatically influences the growth habit of inorganic nanocrystals. The organic–inorganic interface present in these systems is the key to the synthesis of morphology controlled nanocrystals. Ligands can selectively adsorb onto particular facets hindering the growth in the direction perpendicular to that facet. However, the adhesion energy of the ligands should be adjusted to allow dynamic adsorption-desorption during nanoparticle growth, as demonstrated in the past for the synthesis of quantum dots. More importantly, it has also been demonstrated that, for the same functional group, the dynamic effect on the surface of quantum dot nanocrystals is significantly influenced by the ligand chain length. In this article, the authors investigate the effect of the alkyl chain length of carboxylic acid ligands on the growth of NaYF₄ nanocrystals. The much more mobile hexanoic acid (HA) does not effectively passivate the {001} facets leading to rod-shape nanoparticles. With longer alkyl chains ligands, the growth along the c-axis is decreased (see figure below) and the morphology can be almost continuously tuned from rods to very thin disk-shaped crystals. The authors attribute such precise morphology control to the different ligand dynamic as, for longer alkyl chain ligands, the tendency of leaving the (001) crystal surfaces decreases leading to a lower growth on the [001] direction.

Nicola Pinna studied physical chemistry at the Université Pierre et Marie Curie (Paris). He received his Ph.D. in 2001 and in 2002 moved to the Fritz Haber Institute of the Max Planck Society (Berlin). In 2003, he joined the Max Planck Institute of Colloids and Interfaces (Potsdam) before moving to the Martin Luther University, Halle-Wittenberg, as an Assistant Professor of Inorganic Chemistry in 2005. From March 2006 to June 2012 he was researcher at the Department of Chemistry and CICECO of the University of Aveiro and from September 2009 to June 2012 he was also Assistant Professor at the school of chemical and biological engineering Seoul National University. In July 2012 he joined the Department of Chemistry of the Humboldt University in Berlin. His research activity is focused on the development of novel routes to nanostructured materials, their characterization, and the study of their physical properties.

Structural chemistry investigations of macrocyclic compounds such as calixarenes and resorcinarenes are frequently hampered due to problems with crystal growth, and it is quite rare that a successful structural study is supported and complemented by solution- and gas-phase data.  Rissanen and co-workers have produced a systematic and comprehensive exploration of several deprotonated alkyl-resorcinarenes which offers a broad perspective of the structural and chemical behavior of representatives of a ‘classic’ supramolecular system.  The single-crystal studies indicate that the deprotonated macrocycles act as effective hosts for the protonated amines in the solid state and the acid-base behavior in solution is monitored by NMR titrations.  The deprotonated resorcinarenes (monomer and dimer) were observed using EI mass spectrometry in negative ion mode while the 1:1 and 2:1 complexes with the protonated guests were observed in positive ion mode in the gas phase.    

Can self-assembly of copper(II) picolinamide building blocks be controlled?
Marijana Đaković, Diogo Vila-Viçosa, Nuno A. G. Bandeira, Maria José Calhorda, Bojan Kozlevčar, Zvonko Jagličić and Zora Popović 
CrystEngComm, 2013, 15, 8074-8087   

In this paper, Đaković et al examine the structural role played by picolinamide ligands in the directed assembly of a series of Cu(II) based complexes.   The study is supported by an impressive range of experimental and theoretical tools, and offers a comprehensive analysis and evaluation of an important aspect of crystal engineering.    The authors have examined the precise role that different factors play in the assembly of each structural motif and the outcome is a much enhanced understanding of the templating effect of the metal ion as well as of the complementarity of non-covalent interactions.  Finally, the structural work is supported by careful magnetic measurements the results of which are subsequently properly interpreted and rationalized using DFT-based calculations.   

Knowledge-based hydrogen bond prediction and the synthesis of salts and cocrystals of the anti-malarial drug pyrimethamine with various drug and GRAS molecules
Amit Delori, Peter T. A. Galek, Elna Pidcock, Mohit Patni and William Jones 
CrystEngComm, 2013,15, 2916-2928   

The ability to determine which primary intermolecular interactions are most likely to take place given the presence of certain functional groups is of key importance in crystal engineering.  In this study, the authors adopt a knowledge-based approach that takes full advantage of the unique structural information that is provided within the Cambridge Structural Database.  Through the use of hydrogen bond propensity calculations (HBPC), which perform a statistical analysis of the occurrence of specific hydrogen bonds among structures of relevant molecules, it is possible to estimate which hydrogen bonds are most likely to take place between different molecules.   Different hydrogen bonds are assigned propensity scores which provides an avenue for predicting of co-crystals are likely to form between two different molecules and, if so, the type of intermolecular interactions that can be expected within the heteromeric co-crystal.  HBPC calculations were utilized to predict the likelihood of forming co-crystals between the anti-malarial drug pyrimethamine and carbamazepine, theophylline, aspirin, α-ketoglutaric acid, saccharin, coumaric acid, succinimide and L-isoleucine.  The HBPC agreed with the experimental observations indicating that this approach may offer effective and versatile tools for finding new solid forms of high-value chemicals such as pharmaceuticals and agrochemicals.   

Complexities of mechanochemistry: elucidation of processes occurring in mechanical activators via implementation of a simple organic system
Adam A. L. Michalchuk, Ivan A. Tumanov and Elena V. Boldyreva 
CrystEngComm, 2013,15, 6403-6412   

Mechanochemistry is a current ‘hot topic’ which is of considerable interest to both covalent and supramolecular synthetic chemists.  A wide range of chemical transformations are now known to be possible using essentially ‘green’ reaction conditions.  Arguably, most papers that have presented in this field focus on proof-of-principle studies which demonstrate that “functional group ‘A’ can be converted to ‘B’ using the following reaction conditions”, but mechanistic or kinetic studies are still relatively uncommon.  In this paper, however,  Michalchuk et al, present a very detailed examination of the α-glycine : b-malonic acid system which include an analysis of how two key mechanical ‘forces’ – impact and shear – can influence reaction paths and product distribution.  This study clearly demonstrate that what actually happens in a ball mill or through a mortar-pestle treatment is likely to be far more complicated than what is assumed in most studies, notable the role played by the actual mechanoreactor itself.  The results are likely to be of critical importance to many mechanochemical reactions especially in the context of scale-up.   

Synthon identification in co-crystals and polymorphs with IR spectroscopy. Primary amides as a case study
Arijit Mukherjee, Srinu Tothadi, Shaunak Chakraborty, Somnath Ganguly and Gautam R. Desiraju 
CrystEngComm, 2013, 15, 4640-4654

It is probably fair to say that many crystal engineering efforts rely far too heavily on the use of single-crystal X-ray diffraction for product analysis and/or for interpreting the outcome of a particular crystallization or supramolecular synthesis.  However, in this paper, Desiraju and co-workers present a careful and informative study that correlates crystallography with vibrational spectroscopy.  In order to overcome the well-known challenges when using IR spectroscopy for analyzing polymorphs and co-crystals containing multiple synthons, the authors have employed a four-step approach that relies on the use of ‘spectral markers’ that can be directly associated with bonds in specific synthons.  The method is tested on an acid–phenol–pyridine co-crystal system and subsequently utilized for correctly identifying the different synthons in polymorphs of isonicotinamide.        

Halogen bond directionality translates tecton geometry into self-assembled architecture geometry
Marco Saccone, Gabriella Cavallo, Pierangelo Metrangolo, Andrea Pace, Ivana Pibiri, Tullio Pilati, Giuseppe Resnati and Giancarlo Terraneo 
CrystEngComm, 2013,15, 3102-3105 

This paper offers a particularly well-planned and carefully executed strategy for supramolecular synthesis.  One some level, this study may seem overly simplistic and the results may appear to be ‘obvious’ but this is, in my opinion, a testament to the progress that has been made in this field.  We sometimes forget that non-covalent synthesis has to rely on relatively weak and reversible interactions in an environment where solvent molecules are more than capable of disrupting solute-solute biding and, furthermore, that recrystallization is generally favored over heteromeric co-crystallizations.  The fact that we may think that the results presented herein are unsurprising simply means that we are making considerable progress towards finding and developing supramolecular reactions that display a robustness and reliability that we typically associate with named reactions in organic synthesis. 

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Prof. Christer Aakeröy is a University Distinguished Professor at Kansas State University, Manhattan, KS, USA.  He is broadly interested in examining the way in which molecules recognize and bind to each other, and how they communicate and assemble into (occasionally) functional architectures.  He is currently the Chair of the Board of Governors for the Cambridge Crystallographic Data Centre and is an Associate Editor for CrystEngComm.

Self-assembled, monodispersed, flower-like γ-AlOOH hierarchical superstructures for efficient and fast removal of heavy metal ions from water
Yong-Xing Zhang, Yong Jia, Zhen Jin, Xin-Yao Yu, Wei-Hong Xu, Tao Luo, Bang-Jing Zhu, Jin-Huai Liu and Xing-Jiu Huang
CrystEngComm, 2012,14, 3005-3007

In this paper, Yong-Xing Zhang et. al. report the synthesis of self-assembled, monodispersed, flower-like γ-AlOOH hierarchical superstructures for the fast and efficient removal of heavy metal ions Pb(II) and Hg(II) from water via adsorption. These superstructures have been synthesized with BET surface area of 145 m²/g. The authors have shown that over 99.0% of Pb(II) and Hg(II) ions can be removed from aqueous solutions by the flower-like γ-AlOOH within five minutes. Also, as confirmed from adsorption isotherms, the maximal adsorption is ca. 124 mg/g for Pb(II) and 131 mg/g for Hg(II). This work promises to be very useful towards addressing water contamination issues.

Crystallographic analysis of CO₂ sorption state in seemingly nonporous molecular crystal of azacalix[4]arene tetramethyl ether exhibiting highly selective CO₂ uptake
Hirohito Tsue, Hiroki Takahashi, Koichi Ishibashi, Rikako Inoue, Shun Shimizu, Daisuke Takahashi and Rui Tamura
CrystEngComm, 2012, 14, 1021-1026

This paper by Hirohito Tsue et al. describes the highly selective CO₂ sorption by seemingly nonporous crystals of azacalix[4]arene at low temperatures. Single crystal X-ray crystallography was used to carry out an analysis of the CO₂ sorption state at the atomic level, and it was found that weak intermolecular CH/O-interactions had a major role in stabilizing CO₂ molecules inside the crystal.

Metal–organic frameworks: Promising materials for enhancing electrochemical properties of nanostructured Zn₂SnO₄ anode in Li-ion batteries
Xiangzhen Zheng, Yafeng Li, Yuxia Xu, Zhensheng Hong and Mingdeng Wei
CrystEngComm, 2012, 14, 2112-2116

This paper by Wei et al. describes how metal-organic frameworks can improve the electrochemical properties of Li-ion batteries (LIBs). Some interesting highlights of the paper include:

1. This is the first report of the formation of this core/shell structure oin ZTO/ZIF-8 nanocomposites.

2. ZTO/ZIF-8 nanocomposites exhibited larger charge capacities and good cycling performance in LIBs.

3. Porous ZIF-8 on the electrodes helps to release the stress caused by the drastic volume expansion during Li–Sn alloying/de-alloying process, thus enhancing the electrochemical performance of the LIBs.

Hydrothermal aggregation induced crystallization: a facial route towards polycrystalline graphite quantum dots with blue photoluminescence
Zehui Zhang and Peiyi Wu
CrystEngComm, 2012, 14, 7149-7152

In this paper, Wu et al. demonstrated a one step, environmentally friendly method to synthesize graphite quantum dots from graphene oxide, using NH₃ as the passivation agent. A thorough study of the growth mechanism of graphite quantum dots, including a time-dependent experiment, was presented. The authors also explained the role of NH₃ in enhancing the blue luminescence property of the quantum dots.

NiO nanomaterials: controlled fabrication, formation mechanism and the application in lithium-ion battery
Jianmin Ma, Jiaqin Yang, Lifang Jiao, Yuhua Mao, Taihong Wang, Xiaochuan Duan, Jiabiao Lian and Wenjun Zheng
CrystEngComm, 2012, 14, 453-459

This paper is focused on NiO nanomaterials: controlled fabrication, formation mechanism and their application in lithium-ion batteries.

The authors obtained various NiO nanostructures through annealing the corresponding β-Ni(OH)₂ nanostructures at high temperatures. The variety of morphologies in the NiO nanostructures obtained in this work also provided an opportunity to understand the relation between the morphology of the nanostructure and its electrochemical properties.

In terms of the electrochemical performance, these materials have a high initial discharging capacity, although there is still room for improvement in the stability of the material over many charge-discharge cycles.

Conversion of azide to primary amine via Staudinger reaction in metal–organic frameworks
Shunjiro Nagata, Hiroki Sato, Kouta Sugikawa, Kenta Kokado and Kazuki Sada
CrystEngComm, 2012,14, 4137-4141

In this paper, Kazuki Sada et al. describes the facile conversion of azide to primary amine in metal–organic frameworks (MOFs). This post-synthetic surface-selective modification is a useful method for the preparation of MOFs with core-shell structures.

Some important findings include:

1. The conversion of the azide groups into amine by treatment of triphenylphosphine in the presence of water is a new chemical reaction for post-synthetic modification of MOFs.

2. A shorter reaction time induced partial reduction of the azide groups with the preservation of high crystallinity, whereas a longer reaction time induced complete conversion of azide groups.

3. The reactivity of the resulting primary amine groups was confirmed by the further condensation of an activated ester.

Rahul Banerjee received his PhD degree from University of Hyderabad, Hyderabad in 2006 under the supervision of Prof. Gautam R. Desiraju. After postdoctoral work in UCLA with Prof. Omar M. Yaghi (2006-2008), he joined CSIR-National Chemical Laboratory, Pune, India in 2008 as a Scientist. His research interests include the study of structural chemistry with a focus on chemical synthesis to design new materials for hydrogen storage, carbon sequestration and catalysis. Additionally, his group is also engaged in design and synthesis of lightweight materials for storage, capture and proton conduction. Dr. Banerjee is an Editorial board member and an Associate Editor of CrystEngComm. He also served as a co-editor of Acta Crystallographica Section E till 2012.

Effect of dehydration on the mechanical properties of sodium saccharin dihydrate probed with nanoindentation
M. S. R. N. Kiran, Sunil Varughese, U. Ramamurty and Gautam R. Desiraju
CrystEngComm, 2012,14, 2489-2493

In this paper by Desiraju et al., an excellent study was carried out on the effects of dehydration on the mechanical properties of sodium saccharin dihydrate. These effects were probed with nanoindentation. The paper describes several novel features including a thorough study of the mechanical behaviour of sodium saccharin hydrate using nanoindentation with respect to the dehydration process. Time-dependent nanoindentation experiments were carried out to evaluate the variation in the mechanical behaviour of the crystals, initiated by the dehydration process, and the observed variations were correlated with the possible structural changes.

Large organic single crystal sheets grown from the gas–liquid and gas–liquid–solid interface
Hui Shang, Huan Wang, Na Gao, Fangzhong Shen, Xianjie Li and Yuguang Ma
CrystEngComm, 2012,14, 869-874

In this paper, Shang et al. described how large organic single crystal sheets can be grown from the gas–liquid and gas–liquid–solid interface, and highlighted following novel points:

1. A new gas–liquid interface technique is presented for the growth of anthracene (AN) and its doped single crystals.

2. The balanced force and isothermal evaporation of the solvent result in the expansion of the crystal into a three-dimensional stacked structure.

3. The results of X-ray diffraction and optical measurements indicated that such laminated films exhibited higher crystallinity and photoluminescence (PL) efficiency than those obtained by physical vapor transport (PVT) method or original solution growth (SG) method.

4. This crystal growth technique can be extended to the gas–liquid–solid interface to directly grow AN single crystals on electrodes (such as silicon wafers and gold substrates), which may be valuable for the preparation of organic single crystal based devices including light-emitting diodes and field effect transistors.

Hofmeister effects of ionic liquids in protein crystallization: Direct and water-mediated interactions
Magdalena Kowacz, Abhik Mukhopadhyay, Ana Luísa Carvalho, José M. S. S. Esperança, Maria J. Romão and Luís Paulo N. Rebelo
CrystEngComm, 2012,14, 4912-4921

Rebelo et al. have presented an interesting work on ionic liquid assisted crystallization of two proteins, lysozym and ribonuclease A. This paper showcases following interesting points:

1. They have shown experiments on the crystallization of two positively charged proteins, lysozyme and ribonuclease A, using ionic liquids as either crystallization additives or, in particular cases, as precipitating agents.

2. They thoroughly study the effect of Hofmeister anions on stabilizing the positively charged protein and followed by crystallization.

3. The mechanism of crystallization at low and high ionic strength has been nicely described.

Sonocrystallization of zeolitic imidazolate frameworks (ZIF-7, ZIF-8, ZIF-11 and ZIF-20)
Beatriz Seoane, Juan M. Zamaro, Carlos Tellez and Joaquin Coronas
CrystEngComm, 2012,14, 3103-3107

Seoane et al. describes in this paper the synthesis of Zeolitic Imidazolate Frameworks (ZIFs) via sonocrystallization. In comparison to the traditional solvothermal method, this process is a greener approach and requires less energy, as it occurs at a lower temperature. Using this method authors could convert ZIF-7 into ZIF-11 in-situ and obtain a pure phase of ZIF-11, which was not possible by the solvothermal method.

The role of mechanochemistry and supramolecular design in the development of pharmaceutical materials
Amit Delori, Tomislav Friščić and William Jones
CrystEngComm, 2012,14, 2350-2362

In this interesting Highlight, Jones et al. discussed the different aspects of the synthesis of pharmaceutical co-crystals by mechanochemical grinding. The authors provided a nice overview of the topic in a very lucid way and it shows a definite direction of synthesis of pharmaceutical co-crystals. Moreover they have shown that in some cases much variations and freedom can be enjoyed based on the procedure. The authors’ critical review on time-dependent co-crystallization and how grinding a co-crystal with one of the components of the co-crystal to obtain different co-crystals is also worth noting.

Facile synthesis of germanium–graphene nanocomposites and their application as anode materials for lithium ion batteries
Jinsheng Cheng and Jin Du
CrystEngComm, 2012,14, 397-400

This paper by Cheng et al., describes a simple and low-cost method to synthesize Ge nanoparticles/graphene (Ge NPs/GR) nanocomposites under mild conditions. The reduction of sugarcane bagasse (SB) derived graphene oxide nanosheets were accompanied by generation of Ge NPs in one step. This simple and straightforward synthetic approach is likely to find many practical applications. Interesting features of this paper include:

1. A simple, convenient and low-cost method to fabricate GeNPs/GR nanocomposites under mild conditions.

2. Enhancing their electronic conductivity.

3. High-capacity anode material for lithium ion batteries (LIBs).

4. Superior capacity retention of 90% after 15 cycles.

5. Potential application in the development of low-cost and high-performance LIBs.

Facet-selective growth of Cu–Cu₂O heterogeneous architectures
Shaodong Sun, Chuncai Kong, Hongjun You, Xiaoping Song, Bingjun Ding and Zhimao Yang
CrystEngComm, 2012,14, 40-43

In this recent report, Zhimao Yang and co-workers reported a facet-selective growth of Cu–Cu₂O heterogeneous architectures for photodegradation of dye. The authors have demonstrated a facile protocol for the synthesis of facet selective growth of low-cost Cu nanoparticles on the {111} facets of polyhedral 26-facet Cu₂O architectures to form polyhedral 26-facet Cu-Cu₂O architectures, in a simple one pot synthesis reaction. The Cu–Cu₂O architectures prepared with this method also showed better adsorption and photo-degradation of methyl orange as compared to the pristine Cu₂O architectures.

Self-assembled porous hierarchical-like CoO@C microsheets transformed from inorganic–organic precursors and their lithium-ion battery application
Jun Liu, Yichun Zhou, Chunping Liu, Jinbin Wang, Yong Pan and Dongfeng Xue
CrystEngComm, 2012,14, 2669-2674

In an important development towards material synthesis for energy storage, Liu et al. reported a simple, easy, one-step synthesis of interconnected CoO@C micro sheets using a solution phase technique. The porous hierarchical-like CoO@C nanohybrid has been well characterized and judiciously used as an anode material, which is found to exhibit highly reversible capacity along with excellent cycling performance and good rate capability. The hybrid takes advantage of the uniformly encapsulated crystalline CoO within two-dimensional thin carbon layers thereby resulting in an effective intercalation of Li⁺ ions. Here, the synergistic effect of the hierarchical nano-architecture and conducting carbon layer is found to result in an enhanced electrochemical performance of the hybrid.

Rahul Banerjee received his PhD degree from University of Hyderabad, Hyderabad in 2006 under the supervision of Prof. Gautam R. Desiraju. After postdoctoral work in UCLA with Prof. Omar M. Yaghi (2006-2008), he joined CSIR-National Chemical Laboratory, Pune, India in 2008 as a Scientist. His research interests include the study of structural chemistry with a focus on chemical synthesis to design new materials for hydrogen storage, carbon sequestration and catalysis. Additionally, his group is also engaged in design and synthesis of lightweight materials for storage, capture and proton conduction. Dr. Banerjee is an Editorial board member and an Associate Editor of CrystEngComm. He also served as a co-editor of Acta Crystallographica Section E till 2012.