Concomitant and controllable chiral/racemic polymorphs: from achirality to isotactic, syndiotactic, and heterotactic chirality

Handedness-Inverted and Stimuli-Responsive Circularly Polarized Luminescent Nano/Micromaterials Through Pathway-Dependent Chiral Supramolecular Polymorphism

The precise manipulation of supramolecular polymorphs has been widely applied to control the morphologies and functions of self-assemblies, but is rarely utilized for the fabrication of circularly polarized luminescence (CPL) materials with tailored properties. Here, this work reports that an amphiphilic naphthalene-histidine compound (NIHis) readily self-assembled into distinct chiral nanostructures through pathway-dependent supramolecular polymorphism, which shows opposite and multistimuli responsive CPL signals. Specifically, NIHis display assembly-induced CPL from the polymorphic keto tautomer, which become predominant during enol-keto tautomerization shifting controlled by a bulk solvent effect. Interestingly, chiral polymorphs of nanofiber and microbelt with inverted CPL signals can be prepared from the same NIHis monomer in exactly the same solvent compositions and concentrations by only changing the temperature. The tunable CPL performance of the solid microbelts is realized under multi external physical or chemical stimuli including grinding, acid fuming, and heating. In particular, an emission color and CPL on-off switch based on the microbelt polymorph by reversible heating-cooling protocol is developed. This work brings a new approach for developing smart CPL materials via supramolecular polymorphism engineering.

Synthesis, X-ray, Hirshfeld, and AIM Studies on Zn(II) and Cd(II) Complexes with Pyridine Ligands

The synthesis and crystal structures of three heteroleptic complexes of Zn(II) and Cd(II) with pyridine ligands (ethyl nicotinate (EtNic), N,N-diethylnicotinamide (DiEtNA), and 2-amino-5-picoline (2Ampic) are presented. The complex [Zn(EtNic)2Cl2] (1) showed a distorted tetrahedral coordination geometry with two EtNic ligand units and two chloride ions as monodentate ligands. Complexes [Zn(DiEtNA)(H2O)4(SO4)]·H2O (2) and [Cd(OAc)2(2Ampic)2] (3) had hexa-coordinated Zn(II) and Cd(II) centers. In the former, the Zn(II) was coordinated with three different monodentate ligands, which were DiEtNA, H2O, and SO42−. In 3, the Cd(II) ion was coordinated with two bidentate acetate ions and two monodentate 2Ampic ligand units. The supramolecular structures of the three complexes were elucidated using Hirshfeld analysis. In 1, the most important interactions that governed the molecular packing were O···H (15.5–15.6%), Cl···H (13.6–13.8%), Cl···C (6.3%), and C···H (10.3–10.6%) contacts. For complexes 2 and 3, the H···H, O···H, and C···H contacts dominated. Their percentages were 50.2%, 41.2%, and 7.1%, respectively, for 2 and 57.1%, 19.6%, and 15.2%, respectively, for 3. Only in complex 3, weak π-π stacking interactions between the stacked pyridines were found. The Zn(II) natural charges were calculated using the DFT method to be 0.8775, 1.0559, and 1.2193 for complexes 1–3, respectively. A predominant closed-shell character for the Zn–Cl, Zn–N, Zn–O, Cd–O, and Cd–N bonds was also concluded from an atoms in molecules (AIM) study.

Controllable spontaneous resolution in ultrasmall Cu-Ag bimetallic cluster ion pairs from achiral components

Bimetallic cluster ion pairs containing a quaternary phosphonium and an ultrasmall Cu₂Ag₃ anionic cluster protected by thiolates: (PPh₃R'')[Cu₂Ag₃(SR')₆] (R'SH = cyclohexylthiol (CySH), R'' = Ph, 1; Me, 2; Et, 3; Pr, 4; R'SH = tert-butylthiol (^tBuSH) and R'' = Ph, 5) were reported. Without any chiral source, 1 crystallizes as conglomerate crystals with homochiral packings and spontaneous resolution occurs, while four other clusters 2-5 crystallize as racemic crystals with heterochiral packings. These results indicate that racemic and homochiral crystallization in the cluster system could be controlled through fine-tuning internal achiral structural components.

Simultaneous control of polymorph and morphology via gelatin induction for concomitant system: case study of sulfathiazole

Controlling the solid-state properties is particularly important in the pharmaceutical field, where polymorph and morphology have a significant impact on drug properties. Sulfathiazole (ST) is a highly and concomitantly polymorphic...

Isomers of Terpyridine as Ligands in Coordination Polymers and Networks Containing Zinc(II) and Cadmium(II)

The use of divergent 4,2′:6′,4″- and 3,2′:6′,3″-terpyridine ligands as linkers and/or nodes in extended coordination assemblies has gained in popularity over the last decade. However, there is also a range of coordination polymers which feature 2,2′:6′,2″-terpyridine metal-binding domains. Of the remaining 45 isomers of terpyridine, few have been utilized in extended coordination arrays. Here, we provide an overview of coordination polymers and networks containing isomers of terpyridine and either zinc(II) and cadmium(II). Although the motivation for investigations of many of these systems is their luminescent behavior, we have chosen to focus mainly on structural details, and we assess to what extent assemblies are reproducible. We also consider cases where there is structural evidence for competitive product formation. A point that emerges is the lack of systematic investigations.

Enabling photocatalytic activity of [Ru(2,2′:6′,2′′-terpyridine)2]2+ integrated into a metal–organic framework

A multicomponent metal–organic framework is constructed to incorporate the bis-terpyridyl ruthenium motif, which was considered poorly photoactive, through a stepwise reticular synthesis to arouse its photosensitiveness for producing singlet oxygen.

The terpyridine isomer game: from chelate to coordination network building block

The first 4,2':6',4''-terpyridine (4,2':6',4''-tpy) containing coordination polymer was reported over 20 years ago and in the last decade, there has been increased interest in the use of ditopic 4,2':6',4''-tpy ligands as linkers in coordination polymers and 2D-networks. Functionalization in the 4'-position of 4,2':6',4''-tpy is synthetically straightforward, giving access to a large suite of building blocks. Less well explored is the coordination chemistry of 3,2':6',3''-tpy ligands which exhibit greater conformational flexibility than 4,2':6',4''-tpy. One approach to making the transition from 2D- to 3D-networks is to utilize tetratopic bis(4,2':6',4''-tpy) and bis(3,2':6',3''-tpy) ligands which act as 4-connecting nodes. In this highlight, we survey recent progress towards a better understanding of the design principles associated with the use of ditopic and tetratopic 4,2':6',4''-tpy and 3,2':6',3''-tpy containing ligands and their roles both as linkers and nodes in coordination assemblies.

A convenient method for synthesis of terpyridines via a cooperative vinylogous anomeric based oxidation

The presented study is the first report of the synthesis of terpyridines in the presence of a nanomagnetic catalyst instead of harmful reagents. Herein, Fe3O4@O2PO2(CH2)2NH3 +CF3CO2 - as a retrievable nanocatalyst with magnetic properties was applied for the multi-component reaction between acetylpyridine derivatives (2 or 3 or 4-isomer), aryl aldehydes and ammonium acetate under conventional heating conditions in the absence of any solvent. The derived terpyridines were obtained with acceptable yields and brief reaction times via a cooperative vinylogous anomeric based oxidation route. Fe3O4@O2PO2(CH2)2NH3 +CF3CO2 - showed a high capability for recovery and reuse in the mentioned reaction.

Effect of solvent polarity in mechanochemistry: preparation of a conglomerate vs. racemate

Cocrystallization of racemic dl-tartaric acid (dl-ta) and achiral isoniazid (ISN) was investigated using mechanochemistry. Neat grinding (NG) and liquid-assisted grinding (LAG) in the presence of non-polar liquids result in the formation of a conglomerate (ISN·d-ta/ISN·l-ta); whereas LAG with polar liquids yields racemic salt ISN·dl-ta. The effect of solvent polarity and dipole moment in mechanochemistry is discussed.

Rational design, crystal structures and sensing properties of a series of luminescent MOFs based on a flexible tetracarboxylate ligand and N-donor ligands

Six Zn/Cd MOFs were synthesized and characterized. 1–3 are 1D ring chains. 4–5 show 2D bilayer network. 6 possesses a 3D network structure. In particular, 2 demonstrates highly selective and sensitive luminescent sensor towards acetone and Fe³⁺ ion.

Flexible and rigid dicarboxylic acids enable the assembly of achiral and chiral 3D Co(ii) metal–organic frameworks

The homochirality of the 3D Co(ii) MOFs may arise from the rotation of the two phenyl rings in the biphenyl-4,4′-dicarboxylic acid ligand.

A homochiral Zn–Dy heterometallic left-handed helical chain complex without chiral ligands: anion-induced assembly and multifunctional integration

The Zn₃Dy₂ pentanuclear complex evolved into a heterometallic left-handed helical chain multifunctional complex by the template action of perchlorate anion.

Controllable synthesis of nucleotide complex based on pH control: a small-molecule fluorescent probe as an auxiliary ligand to indicate the pre-organization of the nucleotide complex in solution

Different CMP-bpe-M(ii) (CMP = cytidine monophosphate, bpe = bis(4-pyridyl)ethylene, M(ii) = Mn(2+) and Co(2+)) complexes are synthesized controllably based on pH control and well studied by X-ray single-crystal diffraction analysis. Interestingly, the suitable pH conditions are explored by considering the pre-organization modes of CMP, bpe, and M(2+) in aqueous solution by fluorescence spectroscopy based on acid/basic titration. The organic base bpe serves as a small-molecule fluorescent probe to indicate the changes of pre-organization modes along with the changes of the solution acidity. Furthermore, a perfect self-complementary sugar-base hydrogen bond is first reported based on the crystal structure analysis in this work, and different chiralities and SHG activities of CMP-bpe-Mn(ii) complexes obtained at different pH values are studied.

4,2':6',4''-Terpyridines: diverging and diverse building blocks in coordination polymers and metallomacrocycles

4,2':6',4''-Terpyridine (4,2':6',4''-tpy) is one of the less well documented isomers of the well-established bis-chelating 2,2':6',2''-terpyridine. The N-donors of the outer rings in 4,2':6',4''-tpy subtend an angle of 120°, leading to a description of 4,2':6',4''-tpy as a divergent ligand. Because it typically binds metal ions through the outer N-donors only, 4,2':6',4''-tpy is an ideal linker for combination with metal nodes (often geometrically flexible d(10) ions) in coordination polymers and metallomacrocyclic complexes. The facile functionalization of terpyridines in the 4'-position allows access to a suite of 4'-X-4,2':6',4''-tpy ligands in which the 4'-substituent, X, can be selected to assist in directing the metal-ligand assembly process. This overview of recent advances in the chemistry of 4,2':6',4''-tpy and its 4'-substituted derivatives looks at relationships within a series of chiral polymers, competition between the formation of metallocyclic complexes versus polymers, and the use of extended aryl systems to encourage the formation of coordination polymers in which π-stacking of arene domains dominates in the assembly process. Use of metal(ii) acetates is key to the formation of paddle-wheel and larger cluster nodes that direct the assembly of both predetermined and unexpected architectures.

Spontaneous symmetry breaking of Co(ii) metal–organic frameworks from achiral precursors via asymmetrical crystallization

Enantioenriched 3D pseudo-enantiomorphs integrating porosity, chirality and magnetism together with different colour and morphology were obtained through spontaneous symmetry breaking.

Syntheses, topological structures and properties of six metal–organic frameworks constructed from a flexible tetracarboxylate ligand

Six new metal–organic frameworks (MOFs), Co₂O(odip)(py)₂(DMSO)₂·3H₂O (1), Co₂(odip)(H₂O)(DMA)₂·2DMA (2), Co₄(odip)₂(H₂O)₄(DMSO)₂·5DMSO (3), [Zn₂(odip)(DMF)₂(H₂O)]·2DMF·2H₂O (4), Zn₂(odip)(H₂O) (5) and In(odip)·3ACN (6), have been synthesized from the 5,5′-oxydiisophthalic acid (H₄odip) ligand under solvothermal conditions.

Diverse zinc(ii) coordination assemblies built on divergent 4,2′:6′,4′′-terpyridine derivatives: syntheses, structures and catalytic properties

Diverse Zn(ii) metal–organic assemblies of 4,2′:6′,4′′-terpyridine derivatives were structurally characterized and applied for catalytic transesterification of phenyl acetate with alcohols.

Poly[(μ5-3-carboxybenzene-1,2-dicarboxylato)lead(II)]: a helical lead(II) coordination polymer

In the title polymer, [Pb(C9H4O6)]n, the asymmetric unit contains a monomer of a PbIIcation with a doubly deprotonated 3-carboxybenzene-1,2-dicarboxylate dianion (1,2,3-Hbtc2−). Each PbIIcentre is seven-coordinated by seven O atoms of bridging carboxy/carboxylate groups from five 1,2,3-Hbtc2−ligands, forming a distorted pentagonal bipyramid. The PbIIcations are bridged by 1,2,3-Hbtc2−anions, yielding two-dimensional chiral layers. The layers are stacked above each other to generate a three-dimensional supramolecular architectureviaa combination of C—H...O interactions. The thermogravimetric and optical properties are also reported.