CrystEngComm Blog

Inorganic scintillators have desirable properties for the detection of ionising radiation, with potential applications including in nuclear instrumentation.  Scintillators are materials which produce light when they interact with ionising radiation allowing the radiation to be detected and quantified.  However, the methods used to prepare inorganic scintillators are a limitation to the development of further uses.  Growing crystals from the melt provides only a limited range of materials and, while glasses or glass-ceramics allow a wider range, these materials typically have a low light intensity.  Polycrystalline ceramics lie between single crystals and glasses in terms of properties.

In a recent paper, Dosovitskiy et al. demonstrate the preparation of the scintillator YAG:Ce (yttrium aluminium garnet doped with cerium activator) as a polycrystalline ceramic using 3D-printing. This was achieved for Y_2.97Ce_0.03Al₅O₁₂ by co-precipitation followed by heating at 900 ^oC.  A slurry of the resulting powder was then used to 3D-print green bodies using stereolithography.  A so-called green body contains the material of interest along with a binder, the latter being subsequently removed by heating.

After debinding and sintering at 1600 ^oC , the properties of the resulting ceramic material were compared with those of the corresponding YAG:Ce single crystals.  The ceramic showed a scintillation light yield more than 60% higher than that of the single crystals, when using 5.5 MeV α-particles.

Higher activator concentrations can be achieved using this preparation method than in single crystals and this is beneficial to the light yield.  3D printing allows the production of  shapes not available by other methods, free of defects and larger than 1 micrometer.  One possible application of this is in the production of luminescent materials for LED lighting devices.

For more information, see the full paper at:

First 3D-printed complex inorganic polycrystalline scintillator

A. Dosovitskiy, P. V. Karpyuk, P. V. Evdokimov, D. E. Kuznetsova,  V. A. Mechinsky, A. E. Borisevich, A. A. Fedorov, V. I. Putlayev, A. E. Dosovitskiy, M. V. Korjik

DOI:10.1039/C7CE00541E

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Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors. She published a book, ‘Molecules, Medicines and Mischief’, in 2014, on some of the chemicals found in plants and is currently working on a follow-up.

The growth and design of organic crystals is often focused on linear regularity and the optical or electronic properties of the resulting crystals.  Crystallisation is influenced by many factors including the presence of interactions between atoms or groups of atoms.  However, when these are absent or insignificant, another kind of morphology can develop – the curved fractal.   A new paper by Zhang et al. looks at the formation of a curved fractal structure and shows an application of these beyond the scientific realm.

Fractals are defined by the existence of the similar patterns occurring independent of the level of detail observed e.g. as seen in Koch snowflakes.  A series of pyridyl diketones, with varying position of ring nitrogen and substitution, and a β-diketone were prepared and their properties compared.

The luminescent 1-(4-methoxyphenyl)-3-(pyridin-2-yl)propane-1,3-dione (PBDK1) showed, uniquely among the structures studied, a curved fractal structure visible using an electron microscope (seen below in fluorescence mode).  The highest curvature was observed for crystals obtained by evaporation from a solution in acetone at 5.0 mg mL⁻¹ or above, on glass.  Under these conditions, the relatively weak (compared with the 3- and 4-pyridyl analogues) potential intermolecular interactions in PBDK1 can be disrupted by surface tension effects.   This allows molecular slippage and dislocation to occur during crystal growth. The observed curved fractal pattern was transferred onto fabric and the design incorporated in a dress which won first place at the 2016 National Women’s Fashion Design Competition of China.

This work suggests some of the factors involved in the formation of curved fractal structures and also shows that interest in these extends beyond the scientific and into the realm of fashion design.

For more information, read the paper at:

Curved fractal structures of pyridine-substituted β-diketone crystals

Zongzheng Qian, Dongxue Li, Tongqing Xie, Xuepeng Zhang, Yang He, Yuejie Ai and Guoqing Zhang

DOI: 10.1039/C7CE00462A

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Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors. She published a book, ‘Molecules, Medicines and Mischief’, in 2014, on some of the chemicals found in plants and is currently working on a follow-up.

A new method of producing vanillin (3-methoxy-4-hydroxybenzaldehyde) from ferulic acid using a catalytic MOP has been reported.

Vanillin, one of the main chemical components of vanilla, is an important flavouring agent in the food, cosmetic and other industries.  However, although it can be extracted from vanilla pods, less than 1% of the required quantity is obtained in this way.  The remainder is obtained by chemical synthesis using strong oxidising agents and toxic solvents.  Biotechnological production is also possible but there are problems with time-scale, purification and the nature of the bacteria used.   There is, therefore, a demand for cleaner, greener methods of production of vanillin.

This paper reports the production of vanillin in 60% yield from ferulic acid and hydrogen peroxide, when a MOP (metal-organic polyhedron) is used as a catalyst.  Like MOFs (metal-organic frameworks), MOPs are constructed from metal ions and organic ligands but rather than forming frameworks, MOPs are discrete polyhedra. MOFs have been widely studied as potential catalysts but MOPs are practically untried.  Reasons for this include their relative lack of stability and tendency to aggregate.   This paper uses the MOP formed from copper(II) and a ligand from 9H-carbazole-3,6-dicarboxylic acid.  There are also coordinated dimethylformamide and water molecules in the structure.

The catalyst is activated by removing the coordinated solvent molecules by heating.  Ferulic acid and hydrogen peroxide are then reacted in the presence of the MOP.  Best results are obtained when the reaction mixture is sonicated (to reduce possible aggregation of MOP molecules).  A mechanism is proposed starting with coordination of peroxide to the active Cu(II) coordination site (schematically shown above).

The recovered catalyst exhibits a loss of crystallinity and after 5 cycles activity shows a decline.  However, the paper demonstrates the potential for the catalytic use of MOPs for the simple production of vanillin and other compounds.

For more details, read the full paper here:

Synthesis of vanillin via a catalytically active Cu(II)-metal organic polyhedron

Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors. She published a book, ‘Molecules, Medicines and Mischief’, in 2014, on some of the chemicals found in plants and is currently working on a follow-up.

Drugs are often prepared in crystalline form.  However, the relative thermodynamic stability of crystalline compounds can limit water solubility and bioavailability in the body.  An alternative is to make the drugs in an amorphous form that is less stable and more soluble.  Unfortunately, this form tends to revert to the crystalline form during manufacture, processing or storage, which can limit its usefulness.   A new paper by Aiguo Zeng et al., aims to increase understanding of the crystallisation of amorphous drugs, using loratadine (shown below) as a model compound.

Loratadine is a widely-available, non-sedating anti-histamine, used to treat hay-fever and other allergies.  It has been on the market since 1993 and is included in the World Health Organisation’s Model List of Essential Medicines.

Four amorphous samples were prepared by quench-cooling – where molten compounds are rapidly cooled so they have insufficient time to arrange into a crystal lattice.  Study of the samples obtained by cooling at 298 K, 277 K, 253 K and 233 K showed no significant differences in the crystallisation mechanism with quenching temperature.

However, the tendency to crystallise increased with decreasing quench-cooling temperature.  Authors attribute this to the differences in molecular mobility and relaxation of the samples, especially the so-called Johari-Goldstein process of loratadine, involving motion of all atoms in the molecule. This finding will allow the preparation of  loratadine with a lower tendency to crystallise but which retains the beneficial properties of the amorphous form.   It will also inform studies of the amorphous form of other drug molecules.

For more details, read the full paper at:

Ruimiao Chang, Qiang Fu, Yong Li, Mingchan Wang, Wei Du, Chun Chang and Aiguo Zeng  

CrystEngComm, 2017, Advance Article
DOI: 10.1039/C6CE01645F, Paper
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Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors. She published a book, ‘Molecules, Medicines and Mischief’, in 2014, on some of the chemicals found in plants and is currently working on a follow-up.

Many potential applications of metal-organic frameworks (MOFs) rely on the size and nature of the available free volume or pores within the framework structure.  These include use for gas storage or capture and catalysis.   Tuning of the pores is typically achieved by variation of the metal ions or organic ligands.  Lengthening the organic chains can lead to increased pore size but is often limited by a decrease in stability of the framework. A new paper by Yan-Zhen Zheng and colleagues at Xi’an Jiaotong University and the University of Arizona reports a new method of structurally modifying MOFs by insertion of alkali metal ions.

In a series of experiments, a heterometallic MOF with O-containing ligands was modified by the insertion of alkali metal ions into the coordination environment formed by two bridged lanthanide centres.  Initially, 2D or 3D Cu-Pr MOFs were formed with bridging isonicotinate ligands, by reacting isonicotinic acid, CuI and Pr(NO₃)₃ in a range of organic solvents.  The reaction producing one of these MOFs, {[Pr₃(Cu₄I₄)3(ina)₉(DMF)₄](DMF)}n (where ina is isonicotinato and DMF is N,N-dimethylformamide), was then repeated with the addition of NaCl, KCl, RbCl  or CsCl.

In the NaCl and KCl reactions, new MOFs were produced incorporating Na⁺ or K⁺ ions, with void volumes of 53% and 61%, respectively (compared with 10% for the alkali metal ion free MOF).

Reaction involving the next largest ion, Rb⁺, produced an unstable MOF which could not be studied further.  However, reaction with the larger Cs⁺ ion produced a new MOF which didn’t contain this ion, but with a void volume of 59%.

The authors suggest that their method of inducing structural variation using appropriately-sized alkali metal ions should be extendable to other ligand systems for the production of a variety of MOFs with novel structures and functions.

For more information, read the full paper at:
An alkali-ion insertion approach to structurally transform metal–organic frameworks
Yue-Qiao Hu, Mu-Qing Li, Teng Li, Yan-Yan Wang, Zhiping Zheng and Yan-Zhen Zheng
CrystEngComm, 2016, Advance Article
DOI: 10.1039/C6CE00540C
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Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors. She published a book, ‘Molecules, Medicines and Mischief’, in 2014, on some of the chemicals found in plants and is currently working on a follow-up.

Nanolimes, alcoholic dispersions of colloidal Ca(OH)₂ nanoparticles, are commonly used for the conservation of porous materials such as stone and marble.  However, only the basics of the process they undergo – carbonation to produce CaCO₃ – are understood and this limits their potential use.

A new paper by Rodriguez-Navarro looks at the carbonation process in detail, with the aims of increasing the effectiveness of and understanding any limitations in the use of nanolimes in conservation.

Conservation of materials using nanolimes is typically carried out in humid air at room temperature.  Under these conditions, amorphous calcium carbonate (ACC) initially forms.  This can then transform into the metastable vaterite (up to 35 wt%) and a small amount of aragonite (up to 5%), but only in the presence of alcohol.  These polymorphs partially dissolve and the stable polymorph, calcite, precipitates.  Alternatively, calcite can form directly after dissolution of ACC.

Results of the kinetic studies show that the rate-limiting step in the production of calcite is the amount of unreacted Ca(OH)₂.  Although the formation of metastable states might be considered a limitation to the use of nanolimes in conservation, the fast kinetics of the vaterite to calcite conversion (72 % in 10 days) means that almost the full consolidation potential can be reached within weeks of application and it is only over very short time-scales that the performance might be sub-optimal.

These results may also have implications for the design of new CaCO₃ materials for other applications, using syntheses analogous to the multi-step crystallisation shown in the carbonation of nanolimes in the presence of alcohol.

For more information, read the full paper at:

Amorphous and crystalline calcium carbonate phases during carbonation of nanolimes: implications in heritage conservation

Carlos Rodriguez-Navarro, Kerstin Elert and Radek Ševčík

CrystEngComm, 2016, Advance Article
DOI: 10.1039/C6CE01202G, Paper

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Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors. She published a book, ‘Molecules, Medicines and Mischief’, in 2014, on some of the chemicals found in plants and is currently working on a follow-up.

The structure-directing properties of 2,4,6-trimethylpyridine (TMP) for the formation of colloidal C₆₀-fullerene are revealed in a new paper by Penterman and Liddell Watson.

C₆₀-fullerenes can support singlet excited states that recombine to produce a red photoluminescence and also have a high refractive index and transparency.  As such, they have a potential use in colloid-based photonic crystals.  Fullerene microcrystals are typically prepared in a solvent-antisolvent system, where the antisolvent promotes nucleation.  The solvent-antisolvent ratio, concentration of fullerene, temperature and mixing conditions can be varied to produce particles with different morphologies. However, there are not many compatible solvent-antisolvent combinations, limiting the nature of the particles that can form.

In this paper, the effect of adding TMP to the tetralin or mesitylene:2-propanol solvent-antisolvent system, is investigated.  When the solvent is tetralin, TMP plays a dominant role in determining the colloid morphology, monodispersity and crystal structure (an SEM of one fullerene solvate produced is shown below).  In the mesitylene  system, the crystals have well-defined faceting, higher aspect ratios and improved packing efficiency.

The microcrystals show a reduced fluorescence quantum yield and lifetime, which is thought to be a result of greater fullerene packing efficiency. This is enhanced as the polar TMP additive acts as a blocking agent, adsorbing at the solid–liquid interface and slowing the kinetic rates of growth on certain crystallographic planes. The nucleation period is also shortened, supporting monodispersity.

The use of structure-directing agents could allow the production of fullerene microcrystals with diverse internal crystal structures and external forms.  This may allow the development of fullerenes tuned to possess specific properties, including suitability for use as active building blocks for photonic crystals.  The authors are continuing to explore the potential of this application.

For more details, see the full paper at:

CrystEngComm, 2016
DOI: 10.1039/C5CE02122G

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Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors. She has recently published a book on chemicals from plants.

A new paper by Lee et al. who carried out research at the National Central University in China, finally explains the formation of gout.  Gout is an inflammatory arthritic condition caused by the deposition of crystals of monosodium urate monohydrate (MSUM) in joints and tendons.  Traditionally associated with over-indulgent consumption of alcohol and rich food, gout was known as the disease of kings.  It has become more common in recent years, affecting 2-3% of the Western population at some point during their lives.

Development of gout is related to raised levels of uric acid in the blood (hyperuricemia).  However, the mechanism of crystallisation of MSUM and the fact that only some people with hyperuricemia develop gout were not understood, but are now unveiled in this new paper.

The morphology of the MSUM formed from uric acid was studied under various Na⁺ ion concentrations, under conditions mimicking the body (pH 7.4, 37^oC).  The formation of a metastable “beachball structure” which converts to “urchin-like aggregates” and “bow-like aggregates” depends on the Na⁺ ion concentration and it is suggested that the pathogenesis of gout may be related to the transformation of “beachballs” to needles.

When the pH is lowered by adding lactic acid, which would occur during inflammatory response, uric acid dihydrate (UAD) is formed.  As the pH returns to normal, this converts to MSUM, causing an inflammatory response and generating a self-sustaining cycle, as shown in the diagram below.

The presence of hyaluronate, Na⁺, K⁺ and Ca²⁺ is found to affect the development of gout and a new MSUM “fishtail” morphology was observed in hyaluronate-, Na⁺– and Ca²⁺– containing solutions.  A highly water soluble hyaluronate-Ca-urate complex was identified and authors suggest that disruption of this complex would lead to MSUM deposition, causing gout.  Thus, people could have hyperuricemia but not develop gout, if their physiological conditions maintain the complex.

For more information, see the paper at:

The culprit of gout: triggering factors and formation of monosodium urate monohydrate

Meng Hsiu Chih, Hung Lin Lee and Tu Lee

CrystEngComm, 2016, Advance Article
DOI: 10.1039/C5CE01656H, Paper

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Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors. She has recently published a book on chemicals from plants.

A new red-emitting nanophosphor with potential use in white light-emitting diodes (LEDs) has recently been reported by Mi and colleagues.

White LEDs are used for lighting as they use little energy, have high brightness and long lifetimes and are considered environmentally friendly. Currently, these LEDs consist of a combination of a yellow-emitting phosphor and a blue LED chip. However, the lack of a red component is problematic, leading to a low colour rendering index (in other words, some colours do not appear naturalistic) and a high colour temperature (giving light a blue hue). Other possible methods of generating white LEDs that use red phosphors are limited by the low stability and efficiency of commercial sulphide-based red phosphors. Now, Mi and colleagues report an efficient and stable europium-based red phosphor that could solve the problem and improve the suitability of white LEDs for certain medical applications.

The phosphor Ca₉Eu(PO₄)₇ was prepared using hydrothermal methods from calcium- and europium- nitrates and phosphoric acid. It shows a red emission at 616nm under excitation at 397nm. This is attributed to the ⁵D₀ →⁷F₂ transition in Eu³⁺, which will only happen when the Eu ion occurs in sites without inversion symmetry (as it is parity forbidden).

When the phosphor was doped (in other words, when Eu was partially replaced by Gd, La or Y), the emission intensity decreased. The pH value of the synthesis reaction was found to alter the morphology of the phosphor (see the diagram below) from rods to spheres, which had different luminescence properties. The most favourable properties were obtained from rods obtained at pH 7, attributed to the smallest number of lattice defects being formed at this pH. The rods are approximately 100nm long with an aspect ratio (long axis length to width ratio) of 2.5. This phosphor shows a good colour saturation index (R = 2.4) and future studies to optimise its properties could lead to potential application in white LEDs.

For more details read the full paper at:

Hydrothermal synthesis and photoluminescence properties of Ca₉Eu(PO₄)₇ nanophosphors
Jiacheng Sun, Xiaoyun Mi, Lijian Lei, Xiaoying Pan, Shuyi Chen, Zan Wang, Zhaohui Bai and Xiyan Zhang
CrystEngComm, 2015
DOI: 10.1039/C5CE01289A

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Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors. She has recently published a book on chemicals from plants.