Chiral Crystal Structure of aP212121Kryptoracemate Iron(II) Complex with an Unsymmetric Azine Ligand and the Observation of Chiral Single Crystal Circular Dichroism

Sunatsuki, Yukinari; Fujita, K.; Maruyama, Hisashi; Suzuki, Takayoshi; Ishida, Hiroyuki; Kojima, Masayasu; Glaser, Rainer

doi:10.1021/cg500635q

Cited by 15 publications

(10 citation statements)

References 18 publications

(12 reference statements)

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“…In a survey of the Cambridge Structural Database (CSD), only 181 kryptoracemates structures have been identified showing that they represent only 0.1% of structures deposited in CSD . This fact agrees with the rarity of reports involving racemate and kryptoracemates as polymorphs in the literature. ,,,− In these research articles, chirality and symmetry have been attributed to different structural features of these compounds. While the chiral space group of racemates generates only one enantiomer in the asymmetric unit (ASU), the kryptoracemates show Z ′ > 1, and in most of them (about 60%) they exhibit a pseudosymmetric relationship between the enantiomers. ,, In addition, the self-assembly of chiral molecules in racemic chains motifs and their supramolecular chirality are the main structural differences between these polymorphs. ,, The formation of such polymorphs of racemic systems is well recognized, but they remain relatively unexplored.…”

Section: Introductionsupporting

confidence: 87%

Rare Case of Polymorphism in a Racemic Fluoxetine Nitrate Salt: Phase Behavior and Relative Stability

Carvalho

Ellena

Yufit

et al. 2016

Crystal Growth & Design

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Polymorphism in racemic pharmaceutical compounds is relatively unexplored. However, this phenomenon may provide an additional tool to crystal engineering, opening the doors to rational design of chiral resolution, chiral enrichment, and chiral purification of pharmaceutical compounds. In this work we report two racemic polymorphs occurring for the nitrate salt of the antidepressant drug fluoxetine (FLX): a racemate (P2 1 /n, Z = 4, Z′ = 1) and a kryptoracemate (Pca2 1 , Z = 4, Z′ = 2). The relative stability of these polymorphs was established through a combination of techniques, namely, differential scanning calorimetric (DSC), thermogravimetric analysis (TGA), hot stage microscopy (HSM), and solubility measurements. Though the two polymorphs share some structural features, the N + −H•••O − hydrogen bonds have created dissimilar racemic motifs in their packing, resulting in different enantiomer orientations. The racemate is more stable over the temperature ranges we studied and is monotropically related to kryptoracemate. In our experiments, the obtaining of non-centrosymmetric lattice of racemic fluoxetine nitrate was shown to be dependent on kinetic factors. The thermodynamic relationships between both polymorphs were further confirmed by measuring their water solubility at 20 and 37 °C.

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Section: Introductionsupporting

confidence: 87%

Rare Case of Polymorphism in a Racemic Fluoxetine Nitrate Salt: Phase Behavior and Relative Stability

Carvalho

Ellena

Yufit

et al. 2016

Crystal Growth & Design

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“…However, as was expected, all attempts to prepare the compounds HL R with this method failed to isolate the desired compounds, because the reaction gave a complicated mixture of the products ( Figure S1 in the Supplementary Materials ) which were hard to be separated by any purification method. In a previous study [ 30 ], we serendipitously found that the reaction in the presence of iron(II) salts gave selectively the crystals of a Fe II complex bearing unsymmetric azine, [Fe(HL Me ) 2 ](PF 6 ) 2 ·1.5H 2 O. To clarify the role of transition-metal salts in the selective formation of a certain complex, we used a nickel(II) chloride for the preparation of (2-pyridyl)(4-imidazolyl)azine complexes.…”

Section: Resultsmentioning

confidence: 99%

“…Pyridyl ketazine is one of the unique azine-based ligands that have been explored by several researchers for its coordinating abilities and modes, thus paving way for the investigation of several azine-based ligands for their unique coordination chemistry [ 25 , 26 , 27 ]. Our previous studies reported a series of mono- and dinuclear iron(II) complexes with imidazole-4-carbaldehyde azine and other imidazole groups as azine ligands showcasing different modes of coordination towards the iron(II) in the various complexes [ 28 , 29 , 30 ].…”

Section: Introductionmentioning

confidence: 99%

“…Recently, we have investigated the chemistry of pyridyl and imidazolyl azine-based ligands, where an unprecedented selective synthesis of the unsymmetric (2-pyridyl)(2-methyl-4-imidazolyl)azine is obtained in an excellent yield with an interesting bonding mode [ 30 ]. Pursuing our interest in the unsymmetric azine-based ligand, we attempted to synthesize the corresponding nickel(II) complexes bearing 2-pyridylmethylidenehydrazono-(4-imidazolyl)methane (HL H ) and 2-pyridylmethylidenehydrazono-(2-methyl-4-imidazolyl)methane (HL Me ).…”

Section: Introductionmentioning

confidence: 99%

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Selective Formation of Unsymmetric Multidentate Azine-Based Ligands in Nickel(II) Complexes

2022

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A mixture of 2-pyridine carboxaldehyde, 4-formylimidazole (or 2-methyl-4-formylimidazole), and NiCl2·6H2O in a molar ratio of 2:2:1 was reacted with two equivalents of hydrazine monohydrate in methanol, followed by the addition of aqueous NH4PF6 solution, afforded a NiII complex with two unsymmetric azine-based ligands, [Ni(HLH)2](PF6)2 (1) or [Ni(HLMe)2](PF6)2 (2), in a high yield, where HLH denotes 2-pyridylmethylidenehydrazono-(4-imidazolyl)methane and HLMe is its 2-methyl-4-imidazolyl derivative. The spectroscopic measurements and elemental analysis confirmed the phase purity of the bulk products, and the single-crystal X-ray analysis revealed the molecular and crystal structures of the NiII complexes bearing an unsymmetric HLH or HLMe azines in a tridentate κ3N, N’, N” coordination mode. The HLH complex with a methanol solvent, 1·MeOH, crystallizes in the orthorhombic non-centrosymmetric space group P212121 with Z = 4, affording conglomerate crystals, while the HLMe complex, 2·H2O·Et2O, crystallizes in the monoclinic and centrosymmetric space group P21/n with Z = 4. In the crystal of 2·H2O·Et2O, there is intermolecular hydrogen-bonding interaction between the imidazole N–H and the neighboring uncoordinated azine-N atom, forming a one-dimensional polymeric structure, but there is no obvious magnetic interaction among the intra- and interchain paramagnetic NiII ions.

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“…These objects can first form from completely achiral subunits assembled in a chiral manner . The formed system can be a conglomerate, in the absence of perturbation or can be driven into a given chirality by a chiral influence. This is the case for foldamers built from achiral monomers, the helicity of which is determined by the absolute configuration of chiral tartrate gemini .…”

Section: Resultsmentioning

confidence: 99%

Solid‐state synthesis of cyclo LD‐diphenylalanine: A chiral phase built from achiral subunits

2020

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The solid-state structure of LL/DD or LD/DL diphenylalanine diluted in KBr pellets is studied by infrared (IR) absorption and vibrational circular dichroism (VCD) spectroscopy. The structure depends on the absolute configuration of the residues. The natural LL diphenylalanine exists as a mixture of neutral and zwitterionic structures, depending on the humidity of the sample, while mostly the zwitterion is observed for LD diphenylalanine whatever the experimental conditions. The system undergoes spontaneous cyclization upon heating at 125 C, resulting to the formation of a diketopiperazine (DKP) dipeptide as the only product. The reaction is faster for LD than for LL diphenylalanine. As expected, LL and DD diphenylalanine react to form the LL and DD enantiomers of cyclo diphenylalanine. Interestingly, the DKP dipeptides formed from the LD or DL diphenylalanine show unexpected optical activity, with opposite VCD spectra for the products formed from the LD and DL reagents. This is explained in terms of chirality synchronization between the monomers within the crystal, which retain the symmetry of the reagent, resulting to the formation of a new chiral phase made from transiently chiral molecules. K E Y W O R D Schirality synchronization, diketopiperazine (DKP), peptides, vibrational circular dichroism (VCD), vibrational spectroscopy

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Chiral Crystal Structure of aP2₁2₁2₁Kryptoracemate Iron(II) Complex with an Unsymmetric Azine Ligand and the Observation of Chiral Single Crystal Circular Dichroism

Cited by 15 publications

References 18 publications

Rare Case of Polymorphism in a Racemic Fluoxetine Nitrate Salt: Phase Behavior and Relative Stability

Rare Case of Polymorphism in a Racemic Fluoxetine Nitrate Salt: Phase Behavior and Relative Stability

Selective Formation of Unsymmetric Multidentate Azine-Based Ligands in Nickel(II) Complexes

Solid‐state synthesis of cyclo LD‐diphenylalanine: A chiral phase built from achiral subunits

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