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17 pages, 18306 KiB

Open AccessArticle

Effect of Molecular Perturbation on Polymorphism: The Case of 8-Halotheophyllines (8-Cl-Tph and 8-Br-Tph)

by Weijian Ye, Chao Zhang, Herman H-Y. Sung, Lawrence W-Y. Wong, Fu Kit Sheong and Ian D. Williams

Crystals 2025, 15(4), 340; https://doi.org/10.3390/cryst15040340 - 3 Apr 2025

Viewed by 244

Abstract

The common alkaloid theophylline (Tph) is known to exist in five polymorphic forms. The structures of its 8-halo analogues were previously unreported. Here, we report three polymorphs for 8-chlorotheophylline (8-Cl-Tph) and an additional distinct one for 8-bromotheophylline (8-Br-Tph). While polymorphs for theophylline are [...] Read more.

The common alkaloid theophylline (Tph) is known to exist in five polymorphic forms. The structures of its 8-halo analogues were previously unreported. Here, we report three polymorphs for 8-chlorotheophylline (8-Cl-Tph) and an additional distinct one for 8-bromotheophylline (8-Br-Tph). While polymorphs for theophylline are dominated by NH---N inter-molecular hydrogen bonds, the halo compounds exclusively exhibit NH---O interactions. 8-Cl-Tph has two related structures with chains N(7)-H(7)---O(2); one is also the stable form for 8-Br-Tph. Polymorphs with a dimeric R₂²(10) ring structure using N(7)-H---O(6) H-bonds exist for all three compounds, though each with distinct 3D packing. DFT calculations indicate that the alkaloid ring nitrogen N(9) is a weaker base in 8-halo compounds, disfavoring NH---N interactions in their polymorphic forms. Full article

(This article belongs to the Special Issue Crystalline Materials: Polymorphism)

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11 pages, 2160 KiB

Open AccessArticle

Polymorphism and the Phenomenon of Whole-Molecule Disorder Revealed in a Novel Dipodal Thiopyridine Ligand

by Simran Chaudhary, Renny Maria Losus and Liliana Dobrzańska

Crystals 2025, 15(4), 289; https://doi.org/10.3390/cryst15040289 - 22 Mar 2025

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Abstract

We report two polymorphs (α and β) of a novel bipodal ligand, 1,4-bis(thiopyridine)benzene, which were isolated from the same methanolic solution. Single-crystal X-ray analyses revealed the phenomenon of positional whole-molecule disorder occurring in form α, which comes down to packing [...] Read more.

We report two polymorphs (α and β) of a novel bipodal ligand, 1,4-bis(thiopyridine)benzene, which were isolated from the same methanolic solution. Single-crystal X-ray analyses revealed the phenomenon of positional whole-molecule disorder occurring in form α, which comes down to packing disorder. Computational calculations were carried out to compare the crystal lattice energies of the isolated polymorphs. The energetically more stable form β has a higher packing efficiency and shows an increased number of hydrogen bonds compared with both components of form α, the packing of which is dominated by van der Waals interactions. Supportive bulk studies, such as thermal analysis and powder X-ray diffraction, were also performed. Full article

(This article belongs to the Special Issue Crystalline Materials: Polymorphism)

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20 pages, 4387 KiB

Open AccessEditor’s ChoiceArticle

Polymorphism of the Transition Metal Oxidotellurates NiTeO₄ and CuTe₂O₅

by Matthias Weil and Enrique J. Baran

Crystals 2025, 15(2), 183; https://doi.org/10.3390/cryst15020183 - 14 Feb 2025

Viewed by 487

Abstract

As part of crystal growth experiments on transition metal oxidotellurates using chemical vapor transport reactions or hydrothermal conditions, single crystals of Ni^IITe^VIO₄ and Cu^IITe^IV₂O₅ were obtained for the first time in the [...] Read more.

As part of crystal growth experiments on transition metal oxidotellurates using chemical vapor transport reactions or hydrothermal conditions, single crystals of Ni^IITe^VIO₄ and Cu^IITe^IV₂O₅ were obtained for the first time in the form of new modifications, as revealed by crystal structure determinations from X-ray data. In the course of these investigations, the crystal structure model of the only phase of Ni^IITe^VIO₄ reported so far (from now on named α-) was corrected. Both α-(space group P2₁/c, Z = 2) and the new β-polymorph of Ni^IITe^VIO₄ (space group I4₁/a, Z = 8) can be considered derivatives (hettotypes) of the rutile structure (aristotype), as shown by detailed symmetry relationships. For CuTe₂O₅ also, only one crystalline phase has been described so far (from now on named α-) that corresponds to the mineral rajite (space group P2₁/c, Z = 2). Its anion comprises two different trigonal-pyramidal TeO₃ groups linked through corner-sharing into a ditellurite unit. The anion part of the new β-CuTe₂O₅ modification (space group P2₁/c, Z = 2), likewise, comprises two Te^IV atoms but is more complex. Here, one Te^IV atom exhibits a coordination number of 4 and is part of a

{}_{\propto}^{1}[

TeO_2/2O_2/1] chain, and the other has a coordination number of 5 and is part of a

{}_{\propto}^{1}[

TeO_2/2O_3/1]₂ dimer. The two types of anions are linked into a tri-periodic framework where both Te^IV atoms are stereochemically active. The α- and β-CuTe₂O₅ modifications show no closer structural relationship, which is also reflected in their clearly different Raman spectra. Data mining for knowledge discovery in a structure database reveals that polymorphism is a rather common phenomenon for the family of inorganic oxidotellurates. Full article

(This article belongs to the Special Issue Crystalline Materials: Polymorphism)

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15 pages, 16928 KiB

Open AccessArticle

Four Polymorphs of the Bioactive Diuretic Drug 4-Chloro-5-chlorosulfonyl Salicylic Acid

by Maria Olimpia Miclaus, Gheorghe Borodi and Alexandru Turza

Crystals 2025, 15(2), 136; https://doi.org/10.3390/cryst15020136 - 26 Jan 2025

Viewed by 537

Abstract

4-chloro-5-chlorosulfonyl salicylic acid [C₇H₄Cl₂O₅S] is a derivative of salicylic acid and a diuretic agent. Its ability to form polymorphs through recrystallization from various solvents was demonstrated. As a result, four polymorphs were successfully obtained and [...] Read more.

4-chloro-5-chlorosulfonyl salicylic acid [C₇H₄Cl₂O₅S] is a derivative of salicylic acid and a diuretic agent. Its ability to form polymorphs through recrystallization from various solvents was demonstrated. As a result, four polymorphs were successfully obtained and analyzed using single-crystal X-ray diffraction and powder X-ray diffraction, which represents a novelty regarding the polymorphism of this compound of pharmaceutical interest. The solid-state properties were investigated by evaluating crystal lattice energies and intermolecular interactions. Full article

(This article belongs to the Special Issue Crystalline Materials: Polymorphism)

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17 pages, 5478 KiB

Open AccessArticle

Crystallographic and Thermal Studies of the Polymorphs of Tetraoxa[4]arene with Meta-Phenylene Linkers

by Yuki Ishida, Tadashi Kawasaki and Akiko Hori

Crystals 2024, 14(12), 1032; https://doi.org/10.3390/cryst14121032 - 28 Nov 2024

Cited by 1 | Viewed by 787

Abstract

The three isomers of the tetraoxa[4]arene derivative, C₂₄H₁₆O₄, which consist of two m-phenylenes and two phenylenes (meta 1, para 2, ortho 3), represent not only intriguing fundamental structures that induce molecular recognition toward [...] Read more.

The three isomers of the tetraoxa[4]arene derivative, C₂₄H₁₆O₄, which consist of two m-phenylenes and two phenylenes (meta 1, para 2, ortho 3), represent not only intriguing fundamental structures that induce molecular recognition toward non-porous adaptive crystals, but also attractive candidates for crystallographic polymorphism. In this study, we crystallized isomers 2 and 3, in comparison to isomer 1, in order to understand their stable orientations and the corresponding intermolecular interactions in the crystalline state. For example, m-phenylene derivative 1 exhibits polymorphism with both prismatic and block-shaped crystals. Therefore, we prepared p-phenylene derivative 2 and o-phenylene derivative 3, and their structures were fully characterized by SC-XRD, revealing two polymorphs of derivative 2, namely prismatic crystal 2-I and block-shaped crystal 2-II, along with changes to the crystal lattice parameters (2-Ia, 2-Ib, and 2-Ic) based on temperature dependence. In all of its crystal forms, derivative 2 adopts an O-shaped planar structure, where the p-phenylene units face each other. This suggests that the packing mode during the early stages of crystallization, rather than due to any remarkable changes in the molecular structure, directly affects the bulk crystal morphology. On the other hand, derivative 3 adopts a U-shaped vent structure and, to the best of our knowledge, does not form polymorphs. The Platon and Hirshfeld surface analyses indicated that the contributions to the crystal packing were C···C (av. 37.3% for 2-Ia, av. 38.2% for 2-II, and 18.7% for 3), C···H/H···C (av. 37.3% for 2-Ia, av. 38.2% for 2-II, and 18.7% for 3), and O···H/H···O (av. 17.8% for 2-Ia, av. 19.6% for 2-II, and 19.4% for 3), highlighting significant intermolecular CH···π interactions and pseudo-hydrogen bonding forms for derivative 2 and π···π interactions for derivative 3. Full article

(This article belongs to the Special Issue Crystalline Materials: Polymorphism)

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17 pages, 2970 KiB

Open AccessEditor’s ChoiceArticle

Synthesis and Characterization of New Organoammonium, Thiazolium, and Pyridinium Triiodide Salts: Crystal Structures, Polymorphism, and Thermal Stability

by Madhushi Bandara, Khadijatul Kobra, Spencer R. Watts, Logan Grady, Connor Hudson, Claudina Veas, Timothy W. Hanks, Rakesh Sachdeva, Jorge Barroso, Colin D. McMillen and William T. Pennington

Crystals 2024, 14(12), 1020; https://doi.org/10.3390/cryst14121020 - 25 Nov 2024

Viewed by 965

Abstract

Triiodide salts are of interest for a variety of applications, including but not limited to electrochemical and photochemical devices, as antimicrobials and disinfectants, in supramolecular chemistry and crystal engineering, and in ionic liquids and deep eutectic solvents. Our work has focused on the [...] Read more.

Triiodide salts are of interest for a variety of applications, including but not limited to electrochemical and photochemical devices, as antimicrobials and disinfectants, in supramolecular chemistry and crystal engineering, and in ionic liquids and deep eutectic solvents. Our work has focused on the design of salt–solvate cocrystals and deep eutectic solvents in which the triiodide anion interacts as a halogen bond acceptor with organoiodine molecules. To understand structure–property relationships in these hybrid materials, it is essential to have benchmark structural and physical data for the parent triiodide salt component. Herein, we report the structure and thermal properties of eight new triiodide salts, three of which exhibit polymorphism: tetrapentylammonium triiodide (1a and 1b), tetrahexylammonium triiodide (2), trimethylphenylammonium triiodide (3), trimethylbenzylammonium triiodide (4), triethylbenzylammonium triiodide (5), tri-n-butylbenzylammonium triiodide (6), 3-methylbenzothizolium triiodide (7a and 7b), and 2-chloro-1-methylpyridinium triiodide (8a and 8b). The structural features of the triiodide anion, Raman spectroscopic analysis, and melting and thermal decomposition behavior of the salts, as well as a computational analysis of the polymorphs, are discussed. The polymorphic pairs here are distinguished by symmetric versus asymmetric triiodide anions, as well as different packing patterns. Computational analyses revealed more subtle differences in their isosurface plots. Importantly, this study provides reference data for these new triiodide salts for comparison to hybrid cocrystals and deep eutectic solvents formed from their combination with various organoiodines. Full article

(This article belongs to the Special Issue Crystalline Materials: Polymorphism)

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13 pages, 2959 KiB

Open AccessArticle

β-Yb₂CdSb₂—A Complex Non-Centrosymmetric Zintl Polymorph

by Spencer R. Watts, Larissa Najera, Michael O. Ogunbunmi, Svilen Bobev and Sviatoslav Baranets

Crystals 2024, 14(11), 920; https://doi.org/10.3390/cryst14110920 - 25 Oct 2024

Cited by 2 | Viewed by 1162

Abstract

The ternary Zintl phase, Yb₂CdSb₂, was discovered to exist in two different polymorphic forms. In addition to the orthorhombic α-Yb₂CdSb₂ (space group Cmc2₁) known for its excellent thermoelectric properties, we present the synthesis [...] Read more.

The ternary Zintl phase, Yb₂CdSb₂, was discovered to exist in two different polymorphic forms. In addition to the orthorhombic α-Yb₂CdSb₂ (space group Cmc2₁) known for its excellent thermoelectric properties, we present the synthesis and characterization of the crystal and electronic structure of its monoclinic variant, β-Yb₂CdSb₂. Structural characterization was performed with the single-crystal X-ray diffraction method. β-Yb₂CdSb₂ crystallizes in a monoclinic crystal system with the non-centrosymmetric space group Cm (Z = 33, a = 81.801(5) Å, b = 4.6186(3) Å, c = 12.6742(7) Å, β = 93.0610(10)°) and constitutes a new structure type. The complex crystal structure of β-Yb₂CdSb₂ contrasts with the previously studied β-Ca₂CdPn₂ (Pn = P, As, Sb) polymorphs, although it shares similar structural features. It consists of three different layers, made of corner-sharing [CdSb₄] tetrahedra and stacked in the ABC sequence. The layers are interconnected via [CdSb₃] trigonal planar units. Multiple Yb and Cd atomic sites exhibit partial occupancy, resulting in extensive structural disorder. Valence electron partitioning within the Zintl–Klemm formalism yields the formulation (Yb²⁺)_1.98(Cd²⁺)_1.01(Sb³⁻)₂(h⁺)_0.02, highlighting the nearly charge-balanced composition. Detailed electronic structure calculations reveal the closed band gap and presumably semimetallic nature of β-Yb₂CdSb₂ with the band structure features hinting at potential topological properties. Full article

(This article belongs to the Special Issue Crystalline Materials: Polymorphism)

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17 pages, 6208 KiB

Open AccessArticle

Solid Forms and β-Cyclodextrin Complexation of Oxymetholone and Crystal Structure of Metribolone

by Gheorghe Borodi, Maria Olimpia Miclaus, Marieta Muresan-Pop and Alexandru Turza

Crystals 2024, 14(6), 483; https://doi.org/10.3390/cryst14060483 - 21 May 2024

Cited by 1 | Viewed by 1807

Abstract

Oxymetholone [C₂₁H₃₂O₃] and metribolone [C₁₉H₂₄O₂] are synthetic anabolic-androgenic agents which are included in the steroid class. Their ability to form new solid forms and their possibility to be included in host-guest [...] Read more.

Oxymetholone [C₂₁H₃₂O₃] and metribolone [C₁₉H₂₄O₂] are synthetic anabolic-androgenic agents which are included in the steroid class. Their ability to form new solid forms and their possibility to be included in host-guest β-cyclodextrin complexes was explored. The recrystallization of the compounds in a wide variety of solvents was accomplished. Two oxymetholone polymorphs and one oxymetholone acetic acid solvate were obtained:, while metribolone is reported only in the starting form. Their crystal structures were elucidated using single-crystal X-ray diffraction and the energies of intermolecular interactions were analyzed. Moreover, oxymetholone also showed the ability to be complexed in a new form of oxymetholone-β-cyclodextrin complex. The materials were also investigated by powder X-ray diffraction, DSC/DTA/TGA analysis, and FT-IR spectroscopy. Full article

(This article belongs to the Special Issue Crystalline Materials: Polymorphism)

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16 pages, 8235 KiB

Open AccessArticle

Enumeration of Self-Avoiding Random Walks on Lattices as Model Chains in Polymer Crystals

by Javier Benito, Unai Urrutia, Nikos Ch. Karayiannis and Manuel Laso

Crystals 2023, 13(9), 1316; https://doi.org/10.3390/cryst13091316 - 29 Aug 2023

Viewed by 1635

Abstract

Recent simulation studies have revealed a wealth of distinct crystal polymorphs encountered in the self-organization of polymer systems driven by entropy or free energy. The present analysis, based on the concept of self-avoiding random walks (SAWs) on crystal lattices, is useful to calculate [...] Read more.

Recent simulation studies have revealed a wealth of distinct crystal polymorphs encountered in the self-organization of polymer systems driven by entropy or free energy. The present analysis, based on the concept of self-avoiding random walks (SAWs) on crystal lattices, is useful to calculate upper bounds for the entropy difference of the crystals that are formed during polymer crystallization and thus to predict the thermodynamic stability of distinct polymorphs. Here, we compare two pairs of crystals sharing the same coordination number, n_coord: hexagonal close-packed (HCP) and face centered cubic (FCC), both having n_coord = 12 and the same packing density, and the less dense simple hexagonal (HEX) and body centered cubic (BCC) lattices, with n_coord = 8. In both cases, once a critical number of steps is reached, one of the crystals shows a higher number of SAWs compatible with its geometry. We explain the observed trends in terms of the bending and torsion angles as imposed by the geometric constraints of the crystal lattice. Full article

(This article belongs to the Special Issue Crystalline Materials: Polymorphism)

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12 pages, 2811 KiB

Open AccessCommunication

Structural Investigation of Tetra-n-Butylammonium Perchlorate

by Irene Ling, Alexandre N. Sobolev, Chang Hoong Chek and Jack M. Harrowfield

Crystals 2023, 13(8), 1255; https://doi.org/10.3390/cryst13081255 - 14 Aug 2023

Viewed by 1650

Abstract

The crystal structure of tetra-n-butylammonium perchlorate has been successfully elucidated using single-crystal X-ray diffraction. The compound crystallizes in the triclinic space group P

\bar{1}

with unit cell of dimensions a = 14.2706(7) Å, b = 20.6904(9) Å, c = 39.970(2) Å, α [...] Read more.

The crystal structure of tetra-n-butylammonium perchlorate has been successfully elucidated using single-crystal X-ray diffraction. The compound crystallizes in the triclinic space group P

\bar{1}

with unit cell of dimensions a = 14.2706(7) Å, b = 20.6904(9) Å, c = 39.970(2) Å, α = 89.316(4)°, β = 88.638(4)°, and γ = 87.801(4)°. Although complicated by partial disorder, the structure has remarkable features where columns of some of the perchlorate anions running down [100] lie within what can be regarded as nanotubular entities formed by some of the tetrabutylammonium cations, while the remaining tetrabutylammonium cations lie in parallel columns surrounded by the remaining perchlorate anions, one entity being essentially the inverse of the other. Interactions within the structure have been characterized using Hirshfeld surface analysis and comparisons drawn with other unsolvated salts of the cation. Full article

(This article belongs to the Special Issue Crystalline Materials: Polymorphism)

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16 pages, 5607 KiB

Open AccessArticle

Two Conformational Polymorphs of a Bioactive Pyrazolo[3,4-d]pyrimidine

by Sang Loon Tan, Yee Seng Tan, Jia Hui Ng, Anton V. Dolzhenko and Edward R. T. Tiekink

Crystals 2023, 13(6), 974; https://doi.org/10.3390/cryst13060974 - 19 Jun 2023

Cited by 1 | Viewed by 1533

Abstract

Two monoclinic (P2₁/c; Z′ = 1) polymorphs, α (from methanol) and β (from ethanol, n-propanol and iso-propanol), of a bioactive pyrazolo[3,4-d]pyrimidine derivative have been isolated and characterised by X-ray crystallography as well as by [...] Read more.

Two monoclinic (P2₁/c; Z′ = 1) polymorphs, α (from methanol) and β (from ethanol, n-propanol and iso-propanol), of a bioactive pyrazolo[3,4-d]pyrimidine derivative have been isolated and characterised by X-ray crystallography as well as by a range of computational chemistry techniques. The different conformations observed for the molecules in the crystals are due to the dictates of molecular packing as revealed by geometry-optimisation calculations. The crucial difference in the molecular packing pertains to the formation of phenylamino-N–H···N(pyrazolyl) hydrogen bonding within supramolecular chains with either helical (α-form; 2₁-screw symmetry) or zigzag (β-form; glide symmetry). As a consequence, the molecular packing is quite distinct in the polymorphs. Lattice energy calculations indicate the β-form is more stable by 11 kJ/mol than the α-form. Full article

(This article belongs to the Special Issue Crystalline Materials: Polymorphism)

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12 pages, 5572 KiB

Open AccessArticle

Additive-Assisted Crystallization of 9,10-Diphenylanthracene

by Alina A. Sonina, Darya S. Cheshkina and Maxim S. Kazantsev

Crystals 2023, 13(6), 861; https://doi.org/10.3390/cryst13060861 - 24 May 2023

Cited by 2 | Viewed by 2036

Abstract

Crystallization control of organic conjugated small molecules is in high demand for the engineering of functional materials in organic optoelectronics. Here, we report solution additive-assisted crystallization of a model non-planar aromatic hydrocarbon derivative 9,10-diphenylanthracene. Among the studied series of related aromatic hydrocarbons comprising [...] Read more.

Crystallization control of organic conjugated small molecules is in high demand for the engineering of functional materials in organic optoelectronics. Here, we report solution additive-assisted crystallization of a model non-planar aromatic hydrocarbon derivative 9,10-diphenylanthracene. Among the studied series of related aromatic hydrocarbons comprising pyrene, perylene, anthracene, tetracene, and rubrene, only tetracene revealed clear reproducible effects allowing one to perform selective crystallization of metastable 9,10-diphenylanthracene polymorphs. Additionally, crystallization of 9,10-diphenylanthracene and pyrene produced a stoichiometric co-crystal (PYR–DPA) having a segregated layered molecular packing with alternating 9,10-diphenylanthracene and pyrene layers. Remarkably, the molecular packing of pyrene within the co-crystal is unique and represented by the herringbone motif, whereas the molecular packing in known pyrene polymorphs is represented by π-stacked molecules. The co-crystal also demonstrated a bright photoluminescence with a photoluminescence quantum yield of 51%. Considering the morphology of 9,10-diphenylanthracene crystals obtained and crystal structures of PYR–DPA co-crystal and tetracene, we have proposed the mechanism of additive-assisted polymorphism based on the inhibition of (111) facet of α-DPA and promoting of the layered structure crystallization corresponding to metastable polymorphs (β- and γ-DPA). We highlight the additive-assisted crystallization approach as a powerful tool for the crystal engineering of functional materials for organic optoelectronics. Full article

(This article belongs to the Special Issue Crystalline Materials: Polymorphism)

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11 pages, 2342 KiB

Open AccessArticle

Relative Stability of Pyrazinamide Polymorphs Revisited: A Computational Study of Bending and Brittle Forms Phase Transitions in a Broad Temperature Range

by Aleksandr S. Dubok and Denis A. Rychkov

Crystals 2023, 13(4), 617; https://doi.org/10.3390/cryst13040617 - 4 Apr 2023

Cited by 6 | Viewed by 2758

Abstract

Pyrazinamide may exist in at least four known polymorphic forms, which were obtained experimentally. One of these polymorphs, (α), shows outstanding mechanical properties, demonstrating a significant anisotropic plasticity in a three-point bending test, while the δ form was brittle. Despite a δ → [...] Read more.

Pyrazinamide may exist in at least four known polymorphic forms, which were obtained experimentally. One of these polymorphs, (α), shows outstanding mechanical properties, demonstrating a significant anisotropic plasticity in a three-point bending test, while the δ form was brittle. Despite a δ → α transition as well as β and γ behavior being experimentally studied, the relative stability of pyrazinamide polymorphs remains unclear and even controversial. In this work we provide a pure computational study of the thermodynamic relationships between all four polymorphs as a function of temperature using periodic DFT calculations. It was shown that the β but not the δ form is the most stable at low temperatures. Moreover, the relative stability of the δ form in comparison to α is questioned, showing that the “brittle to bending” δ → α transition was kinetically hindered in the experiments. We show that α and γ polymorphs were stabilized at higher temperatures due to an entropy term. Finally, the calculated stability of the bending α form of pyrazinamide at room temperature was in perfect agreement with previous experiments, which showed a transformation of all other forms to α during six month storage or grinding. Full article

(This article belongs to the Special Issue Crystalline Materials: Polymorphism)

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12 pages, 1702 KiB

Open AccessArticle

Two Crystal Forms of 4′-Methyl-2,4-dinitrodiphenylamine: Polymorphism Governed by Conformational Flexibility of a Supramolecular Synthon

by Ivan V. Fedyanin and Aida I. Samigullina

Crystals 2023, 13(2), 296; https://doi.org/10.3390/cryst13020296 - 10 Feb 2023

Cited by 2 | Viewed by 1846

Abstract

Single crystals of two polymorphic forms of 4′-methyl-2,4-dinitrodiphenylamine were obtained by crystallization and characterized by X-ray diffraction analysis. One of the forms is non-centrosymmetric (space group P2₁2₁2), while the second is centrosymmetric (space group P¯1) and contains [...] Read more.

Single crystals of two polymorphic forms of 4′-methyl-2,4-dinitrodiphenylamine were obtained by crystallization and characterized by X-ray diffraction analysis. One of the forms is non-centrosymmetric (space group P2₁2₁2), while the second is centrosymmetric (space group P¯1) and contains two crystallographically independent molecules in the asymmetric unit. In both forms, the same supramolecular synthon, a dimer linked by bonding N-H···O, O···O, and C-H···O interactions were found. Despite nearly the same connectivity of the bonding interactions, the conformation of the supramolecular synthon is different, including its unavoidably different symmetry in two polymorphs. The comparison of the crystal packing of the orthorhombic polymorph with that of the related 2,4-dinitrodiphenylamine (space group P2₁/n) shows the quasi-isostructurality of the fragments, infinite π-stacks joined by weak non-directional intermolecular interactions. However, the fragments are linked by the supramolecular synthons via either a two-fold axis or an inversion center, which lead to only the partial isostructurality of the crystals. Full article

(This article belongs to the Special Issue Crystalline Materials: Polymorphism)

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Review

Jump to: Research

17 pages, 4834 KiB

Open AccessReview

Advancements in the Research on the Preparation and Growth Mechanisms of Various Polymorphs of Calcium Carbonate: A Comprehensive Review

by Cheng-Gong Lu, Chu-Jie Jiao, Xiu-Cheng Zhang, Jian-Sheng Zheng and Xue-Fei Chen

Crystals 2025, 15(3), 265; https://doi.org/10.3390/cryst15030265 - 13 Mar 2025

Viewed by 519

Abstract

Calcium Carbonate (CC) exhibits broad application prospects and significant market demand due to its diverse polymorphs, each with distinct potential for application in various fields. Consequently, the preparation of CC with specific polymorphs has emerged as a research hotspot. This paper commences with [...] Read more.

Calcium Carbonate (CC) exhibits broad application prospects and significant market demand due to its diverse polymorphs, each with distinct potential for application in various fields. Consequently, the preparation of CC with specific polymorphs has emerged as a research hotspot. This paper commences with an overview of the structure of CC, followed by an analysis of the advantages and disadvantages, as well as the mechanisms, of common preparation methods such as physical methods, chemical carbonation processes, and double displacement reactions. Special emphasis is placed on elucidating the influence of polymorph control agents (including inorganic ions, sugars, alcohols, and acids), process conditions (temperature, stirring rate, pH, and solution mixing rate), and reactor configurations (rotating packed beds and high-gravity reactors) on the polymorph regulation of CC. This paper points out how these factors alter the crystal formation process. Furthermore, it introduces the nucleation and growth control of CC crystallization, analyzing the mechanisms underlying these two processes. Research indicates that the carbonation process is currently a relatively mature preparation technique, with multiple factors synergistically influencing the polymorph and particle size of CC. Future efforts should focus on further improving production processes, exploring novel polymorph control agents, and delving deeper into the intrinsic mechanisms of polymorph control to achieve efficient preparation of diverse CC types. Full article

(This article belongs to the Special Issue Crystalline Materials: Polymorphism)

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