Helical Coordination Polymers Research Articles

Solvent-controlled assembly of helical coordination polymers based on lactate synthon from two-dimensional layer to three-dimensional framework

Compound (R)-4-(1-carboxyethoxy)-2-methylbenzoic acid ((R)-H2cma) was prepared from (S)-methyl lactate and 4-hydroxy-2-methylbenzoic acid. (R)-H2cma as chiral synthon assembled with 1,3-di(pyridin-4-yl)propane (1,3-dpp) and Ni2+ ions to obtain helical chiral complexes {[Ni2((R)-cma)2(1.3-dpp)2]·H2O}n (HU18-R) and {[Ni2((R)-cma)2(1.3-dpp)2(H2O)]·3H2O}n (HU19-R) in different solvent systems. Single crystal tests revealed that HU18-R is a two-dimensional (2D) structure with two independent Ni2+ centers and HU19-R is a three-dimensional (3D) framework containing dinuclear [Ni2(CO2)2(H2O)]2+ clusters. Four types of helices were formed in HU18-R and HU19-R by chiral transfer or induction. In HU18-R, small right-handed (R)-cma-Ni chain and large right-handed (R)-cma-Ni-1.3-dpp chain were constructed by chiral transfer. For HU19-R, helical nano-channel based on achiral 1.3-dpp ligands and Ni2+ ions was obtained from chiral induction method and small (R)-cma-Ni chain was built from chiral transfer. As semi-conducting materials, HU18-R and HU19-R indicate strong absorption capacity for UV–vis light and low-impedance properties. Under UV light, they have noticeable catalytic effects for degradation of methylene blue (MB). Moreover, magnetic tests confirmed that HU18-R and HU19-R have ferromagnetic and antiferromagnetic properties, respectively.

Metallo‐Supramolecular Helical Fibres from Chiral Phenylacetylene Monomers: Cation Induced Self‐Assembly

AbstractChiral metallo‐supramolecular fibres can be easily obtained by mixing a chloroform solution of a phenylacetylene monomer (PA) that bears a chiral sulfoxide group as pendant, with different equivalents of a methanolic solution of AgClO4. Thus, while the PA is found molecularly dissolved in chloroform, the addition of Ag+ ions induce its aggregation through the formation of an axially chiral metallo‐supramolecular aggregate with high thermal stable properties. In this case, the ability of the metal ion to coordinate the PA triple bond, combined with the argentophilicity of the metal ion and the planarity of the phenylacetylene drives to the formation of a helical coordination polymer, whose P or M axial chirality is determined by the chirality of the sulfoxide used as substituent of the PA. Depending on the PA/Ag+ (mol/mol) ratio, it is possible to tune the morphology of the metallo‐supramolecular aggregate from chiral fibers to chiral gel.

Metallo-Supramolecular Helical Fibres from Chiral Phenylacetylene Monomers: Cation Induced Self-Assembly.

Chiral metallo-supramolecular fibres can be easily obtained by mixing a chloroform solution of a phenylacetylene monomer (PA) that bears a chiral sulfoxide group as pendant, with different equivalents of a methanolic solution of AgClO4 . Thus, while the PA is found molecularly dissolved in chloroform, the addition of Ag+ ions induce its aggregation through the formation of an axially chiral metallo-supramolecular aggregate with high thermal stable properties. In this case, the ability of the metal ion to coordinate the PA triple bond, combined with the argentophilicity of the metal ion and the planarity of the phenylacetylene drives to the formation of a helical coordination polymer, whose P or M axial chirality is determined by the chirality of the sulfoxide used as substituent of the PA. Depending on the PA/Ag+ (mol/mol) ratio, it is possible to tune the morphology of the metallo-supramolecular aggregate from chiral fibers to chiral gel.

Assembly of 1D Helical Energetic Coordination Polymers Using a Flexible Bridged Furazan-triazole Cation.

Two new energetic coordination compounds with 1D helical chain structures have been synthesized. First, the polyamine precursor 4,5-diamino-2-((4-amino-1,2,5-oxadiazole-3-yl)methyl)-2,4-dihydro-3H-1,2,4-triazole-3-imino chloride salt (TATAF-Cl) is obtained by incorporating 4-(chloromethyl)-1,2,5-oxadiazol-3-amine with 4H-1,2,4-triazole-3,4,5-triamine. Using a simple hydrothermal method, two energetic complexes, Ag(TATAF)(ClO4)2 (ECP-1) and Ag(TATAF)(NO3)2·H2O (ECP-2), with a helical 1D MOF structure of furazan and triazole were synthesized. Compounds ECP-1 and ECP-2 have relatively high nitrogen and oxygen content (N + O%: 52.04%, 61.04%), excellent crystal density (2.229 g cm-3, 2.116 g cm-3 at 298 K) and high heat of detonation (1.18 kcal g-1, 1.06 kcal g-1), good detonation performance (P: 35.34 GPa, 29.52 GPa; Dv: 8412 m s-1, 7794 m s-1), and moderate sensitivity (IS: 8 J, 13 J; FS: 72 N, 64 N). Structurally, the Ag+ of the two ECPs is coordinated with two energetic cations, two perchlorates, or one nitrate via tetragonal coordination to form a single helical structure that is interspersed up and down in two directions.

Synthesis of hydrogen bonded copper(II) coordination polymer: Photocatalytic degradation of Rose Bengal dye and luminescent sensing of Hg+2, Cr2O72−, and nitrofurantoin

A new helical coordination polymer, [Cu(Or)(H2O)3]n (KA@CP-ARS) has been synthesized at room temperature and examined using single-crystal X-ray diffraction (SC-XRD) and other analytical techniques. KA@CP-ARS formed 1D helical type structure via coordination bonding as well as a 3D supramolecular network through hydrogen bonding interactions. KA@CP-ARS manifested as a remarkable luminescent sensor for volatile organic compounds (VOCs), 3-Nitrophenol, Cr2O72−, Hg2+, creatinine, nitrofurantoin and sucrose (200 mg/dl) in particular along with the remarkable photocatalytic degradation of Rose Bengal (RB) dye with 96.54% efficiency. Overall this study demonstrates that the synthesized Cu-orotate coordination polymer has good luminescent sensing and catalytic degradation activity, therefore could be employed for a range of applications such as sensing of biomolecules like sucrose and photocatalysis of toxic dyes.

Coordination Sphere Flexibility Leads to Elastic Deformation in a One-Dimensional Coordination Polymer Crystal

Coordination polymers exhibiting mechanical flexibility including elastic or plastic bending are rare. Here, we report an example of a mechanically flexible one-dimensional coordination polymer that shows elastic bending. Quantitative insights on the inter and intra-chain bonding as well as structural flexibility from a combination of techniques including variable temperature single crystal X-ray diffraction (XRD), high-pressure crystallography (ambient─15 GPa), synchrotron micro-XRD mapping of the bent crystal, and high-resolution synchrotron X-ray charge density analysis show that the helical coordination polymer behaves like a spring when subjected to external stimuli. Changes that occur with the variation of temperature, pressure, or bending, however, result in very different mechanistic changes. The exceptional coordination sphere flexibility rendered by the presence of Jahn–Teller distorted coordination bonds leads to the flexibility of the polymer.

Coordination-Driven Self-Assembly of Complexes Constructed from Two Helical Ligands: Synthesis, Structures, and Selective Gas Adsorption Properties.

Two helical ligands (L1 and L2) were designed and synthesized by a Schiff base condensation reaction. Eight complexes, {[Zn(L1)I2]·H2O}n (1), [Cd2(L1)2I4(CH3OH)2] (2), [Hg2(L1)2I4] (3), [Ag(L1)NO3]n (4), [Ag2(L1)2(NO3)2DMSO]·H2O (5), {[Zn2(L2)2Cl4]·2CHCl3}n (6), {[Ag(L2)]·NO3}n (7), and {[Ag(L2)NO3]·CH3OH}n (8), were synthesized and characterized based on these two ligands. The crystal structures show that both Schiff base compounds exist as racemic ligands with equal amounts of P- and M-helicity, and the assembly of these racemic ligands with metal ions can lead to homochiral or heterochiral complexes via a chiral self-recognition or self-discrimination process. Complexes 2, 3, and 5 exist as heterochiral metallomacrocycles with a figure-eight conformation. Complexes 1, 6, and 8 exist as one-dimensional (1D) homochiral helical chain coordination polymers, while complexes 4 and 7 exist as 1D heterochiral helical chain coordination polymers. Furthermore, gas and vapor adsorption measurements show that all of the synthesized complexes exhibit good selective adsorption capacities toward methanol and ethanol vapor over N2, H2, and O2.

The Anion-Directed Self-Assembly of tubular helical silver (I)-Based coordination polymers and the adsorption properties of hazardous substances

The controlled synthesis of topologically-structured helical coordination polymers (CPs) using versatile organic linkers and a metal centre, has recently attracted considerable attention. In this study, we design and synthesize a flexible tripodal ligand L1 (where L1 = 1, 3, 5-tris(2-pyridylsulfanylmethyl)-2, 4, 6-triethylbenzene) with an N, S cooperative chelation coordination geometry. In combination with silver salts in the presence of anions (nitrate and hexafluorophosphate), silver(I)-based tubular-shaped coordination polymers 1 ([Ag(NO3)(DMF)L12]n) and 2 ({[Ag(CH3CN)L12]•PF6}n) were precisely constructed through cooperative Ag-N/Ag-S and anion coordination interactions, which influenced the helical structures. Both single-stranded helical silver (I)-based CPs were characterised by NMR, PXRD, XPS, and FT-IR spectroscopy. CPs 1–2 have an irregular tube-like channel within their crystal structure which can capture iodine (adsorption capacity 0.27 g/g) and MnO4¯anions (0.25 eq. PF6¯ anions were exchanged) from their aqueous, or hexane, solution.

Lead(II) complexes with Kemp’s tricarboxylate: Can lone pair activity be discerned?

Kemp’s triacid (H3kta; cis,cis-1,3,5-trimethylcyclohexane-1,3,5-tricarboxylic acid) has been used to synthesize three lead(II) complexes under solvo-hydrothermal conditions. [Pb3(kta)Cl3] (1) and [Pb3(H3kta)(kta)2] (2) are both diperiodic coordination polymers displaying hydrophobic surfaces with protruding methyl groups, complex 2 being isomorphous with an SrII complex previously reported. In contrast, [Pb(Hkta)(phen)] (3), where phen is 1,10-phenanthroline, is a monoperiodic, helical coordination polymer. In all cases, PbII cations are in seven- or eight-coordinate environments of predominantly hemidirected nature. The possible effects of the PbII valence shell lone pair are discussed in terms of coordination geometry and Pb⋅⋅⋅H weak interactions as revealed on Hirshfeld surfaces. Only in complex 1 is a short Pb⋅⋅⋅H contact at 2.84 Å possibly indicative of appreciable basicity of the metal ion. All three complexes show similar weak luminescence, apparently independent of the nature of the ligands.

Supramolecular Helical Assemblies of Dirhodium(II) Paddlewheels with 1,4-Diazabicyclo[2.2.2]octane: A Remarkable Substituent Effect on the Helical Sense Preference and Amplification of the Helical Handedness Excess of Metallo-Supramolecular Helical Polymers.

We report unique coordination-driven supramolecular helical assemblies of a series of dirhodium(II) tetracarboxylate paddlewheels bearing chiral phenyl- or methyl-substituted amide-bound m-terphenyl residues with triethylene glycol monomethyl ether (TEG) or n-dodecyl tails through a 1:1 complexation with 1,4-diazabicyclo[2.2.2]octane (DABCO). The chiral dirhodium complexes with DABCO in CHCl3/n-hexane (1:1) form one-handed helical coordination polymers with a controlled propeller chirality at the m-terphenyl groups, which are stabilized by intermolecular hydrogen-bonding networks between the adjacent amide groups at the periphery mainly via a cooperative nucleation-elongation mechanism as supported by circular dichroism (CD), vibrational CD, and variable-temperature (VT) absorption and CD analyses. The VT visible-absorption titrations revealed the temperature-dependent changes in the degree of polymerization. The columnar supramolecular helical structures were elucidated by X-ray diffraction and atomic force microscopy. The helix sense of the homopolymer carrying the bulky phenyl and n-dodecyl substituents is opposite those of other chiral homopolymers despite having the same absolute configuration at the pendants. A remarkably strong "sergeants and soldiers" (S&S) effect was observed in most of the chiral/achiral copolymers, while the copolymers of the bulky chiral phenyl-substituted dirhodium complexes with n-dodecyl chains displayed an "abnormal" S&S effect accompanied by an inversion of the helix sense, which could be switched to a "normal" S&S effect by changing the solvent composition. A nonracemic dirhodium complex of 20% enantiomeric excess bearing the less bulky chiral methyl substituents with n-dodecyl chains assembled with DABCO to form an almost one-handed helix (the "majority rule" (MR) effect), whereas the three other nonracemic copolymers showed a weak MR effect.

Acetonitrile coordination to silver(I) ions of 1‐D coordination polymers with 1,3‐di(nicotinoyloxy)‐2‐methylenepropane

AbstractThe fluorescent molecule 1,3‐di(nicotinoyloxy)‐2‐methylenepropane (L) can be a good candidate for construction of coordination polymers with photoluminescence (PL) properties. Self‐assembly of silver(I) hexafluorophosphate with this ligand in a mixture of methanol and dichloromethane produced a 1‐D helical coordination polymer consisting of [Ag(L)](PF6), whereas crystallization from an acetonitrile‐based medium afforded a 1‐D sinusoidal coordination polymer consisting of [Ag(L)(CH3CN)2](PF6) having intramolecular argentophilic Ag∙∙∙Ag and π∙∙∙π interactions arising from the eclipsed conformation of L. These findings suggest that the final structures of the two products can be controlled by the reaction solvent media rather than the crystallization method or concentration. The physicochemical properties of the present silver(I) compounds were fully characterized by means of infrared spectroscopy, thermogravimetric analysis/differential scanning calorimetry, PL, single‐crystal x‐ray diffraction (XRD), and powder‐XRD measurements.

Distinct Fold-Mode Formation of Crystalline Cu(I) Helical Coordination Polymers with Alternation of the Solid-State Emission Using Shape of the Counter Anions.

One-dimensional cationic coordination polymers have been a promising platform for designing solid-state physical properties through diverse coordination geometries. In particular, the folding mode of the coordination polymers that form a helical structure directly determines the metal-centered coordination environment. Herein, we report N-heterocyclic carbene (NHC) Cu(I) cationic coordination polymers with pyrazine as the linker, which construct a 4-fold or 3-fold helical column in luminescent crystals using octahedral anions (SbF6- and PF6-) or a tetrahedral anion (BF4-), respectively. Single-crystal XRD studies revealed that the folding modes depend on the structural shape of the counteranions, which form H-F interactions between ligands and anions. Indeed, the folding mode change from 4-fold to 3-fold by including a different shape of the counteranions, resulting in red-shifted emission from approximately 580 to 687 nm, which is difficult to modulate in the solid state.

Controllable Macroscopic Chirality of Coordination Polymers through pH and Anion-Mediated Weak Interactions.

Helical architectures with controllable helical sense bias have recently attracted considerable interest for mimicking biological helices and developing novel chiral materials. Coordination polymers (CPs), composed of metal ion nodes and organic linkers, are intriguing systems showing tunable structures and functions. However, CPs with helical morphologies have rarely been explored so far. Particularly, chirality inversion through external stimulus has not been achieved in helical CPs. In this work, we carried out an in-depth investigation on the self-assembly of 1D gadolinium(III) phosphonate CPs using GdX3 (X=Cl, Br, I) and Gd(RSO3 ) (R=CH3 , C6 H5 , CF3 ) as metal sources and R-(1-phenylethylamino)methyl phosphonic acid (R-pempH2 ) as ligand. Superhelices were formed by precise control of the interchain interactions through different intercalated anions. Furthermore, the twisting direction of superhelices could be controlled by synergistic effect of anions and pH. This study may provide a new route to fabricate helical nanostructures of CPs with a desirable chiral sense and help understand the inner mechanism of the self-assembly process of macroscopic helical structures of molecular systems.

Metal‐Coordinated Supramolecular Polymers from the Minimalistic Hybrid Peptide Foldamers

AbstractAvailing the peptide folded architectures to design metal‐coordinated frameworks and cages is restricted due to the scarcity of readily accessible short and stable secondary structures. The secondary structures, α‐helix and β‐sheets, play significant roles in stabilizing tertiary folds of proteins. Designing such helical structures from the short sequences of peptides without having any steric restrictions is exceptionally challenging. Here we reveal the short α,γ‐hybrid tripeptide sequences that manifest stable helical structures without having any sterically constrained amino acids. These short hybrid tripeptides fold into helices even in the presence of two typically β‐sheet favoring Val residues. The hybrid helix consisting of terminal pyridine units coordinates with the metal ions and drives the helical polymerization. Depending on the sequence and the position of N in pyridine moieties, these peptides form selective metallogels with Ag+ and Cu2+ ions. The X‐ray diffracted analysis of the peptide single crystals obtained from the gel matrix reveals that the helical structure is maintained during the self‐assembly process. Further, by varying the counter anion, a 3D helical crystalline coordination polymer with permanent porosity is generated. The findings reported here can be used to design new functional metal‐foldamer coordinated polymers.

Metal-Coordinated Supramolecular Polymers from the Minimalistic Hybrid Peptide Foldamers.

Availing the peptide folded architectures to design metal-coordinated frameworks and cages is restricted due to the scarcity of readily accessible short and stable secondary structures. The secondary structures, α-helix and β-sheets, play significant roles in stabilizing tertiary folds of proteins. Designing such helical structures from the short sequences of peptides without having any steric restrictions is exceptionally challenging. Here we reveal the short α,γ-hybrid tripeptide sequences that manifest stable helical structures without having any sterically constrained amino acids. These short hybrid tripeptides fold into helices even in the presence of two typically β-sheet favoring Val residues. The hybrid helix consisting of terminal pyridine units coordinates with the metal ions and drives the helical polymerization. Depending on the sequence and the position of N in pyridine moieties, these peptides form selective metallogels with Ag+ and Cu2+ ions. The X-ray diffracted analysis of the peptide single crystals obtained from the gel matrix reveals that the helical structure is maintained during the self-assembly process. Further, by varying the counter anion, a 3D helical crystalline coordination polymer with permanent porosity is generated. The findings reported here can be used to design new functional metal-foldamer coordinated polymers.

Helical Coordination Polymers Based on Keggin‐type POMs and N‐donor Ligand

Two new 1D helical coordination polymers based on polyoxometalate were synthesized by self‐assembly of Keggin‐type POMs and copper salts in the presence of triangular N‐heterocyclic derivatives or long‐chain N‐containing carboxylate ligand, that are, (H3O)[{Cu(H2tpim)2}{SiMo12O40}]·0.5H2O [Htpim = 2,4,5‐tri(4‐pyridyl)‐imidazole] (1) and [Cu2(Hcpp)3(cpp)(H2O)][PMo12O40]·2H2O [Hcpp = 1‐(4‐cyanobenzyl)‐3–2‐yl)pyrazole] (2). Their structures were determined by single‐crystal X‐ray diffraction and further characterized by elemental analyses and TG analyses. Compounds 1 and 2 exhibit (1D→2D) interdigitated architectures assembled from 1D helical chains. In compound 1, the achiral 2D interdigitated nets containing left‐ and right‐handed helixes are further interdigitated with each other to form a 3D supramolecular framework. In compound 2, adjacent 2D interdigitated layers with opposite chirality are further extended by supramolecular interactions into a 3D supramolecular network, in which non‐coordinating Keggin‐type POMs as guests are encapsulated.

Temperature-induced solid-to-solid transformation in helical homochiral coordination polymers.

The reactions of (R)- and (S)-4-(1-carboxyethoxy)benzoic acid (H2CBA) with 1,3-bis(2-methyl-1H-imidazol-1-yl)benzene (1,3-BMIB) ligands afforded a pair of homochiral coordination polymers (CPs), namely, poly[[[μ-1,3-bis(2-methyl-1H-imidazol-1-yl)benzene][μ-(S)-4-(1-carboxylatoethoxy)benzoato]zinc(II)] monohydrate], {[Zn(C10H8O5)(C14H14N4)]·H2O}n or {[Zn{(S)-CBA}(1,3-BMIB)]·H2O}n (1-L), and poly[[[μ-1,3-bis(2-methyl-1H-imidazol-1-yl)benzene][μ-(R)-4-(1-carboxylatoethoxy)benzoato]zinc(II)] monohydrate] (1-D). Three kinds of helical chains exist in compounds 1-D and 1-L, which are constructed from ZnII atoms, 1,3-BMIB ligands and/or CBA2- ligands. When the as-synthesized crystals of 1-L and 1-D were further heated in the mother liquor or air, poly[[μ-1,3-bis(2-methyl-1H-imidazol-1-yl)benzene][μ-(S)-4-(1-carboxylatoethoxy)benzoato]zinc(II)], [Zn(C10H8O5)(C14H14N4)]n or [Zn{(S)-CBA}(1,3-BMIB)]n (2-L), and poly[[μ-1,3-bis(2-methyl-1H-imidazol-1-yl)benzene][μ-(R)-4-(1-carboxylatoethoxy)benzoato]zinc(II)] (2-D) were obtained, respectively. The single-crystal structure analysis revealed that 2-L and 2-D only contained one type of helical chain formed by ZnII atoms and 1,3-BMIB and CBA2- ligands, which indicated that the helical chains were reconstructed though solid-to-solid transformation. This result not only means the realization of helical transformation, but also gives a feasible strategy to build homochiral CPs.

Hierarchical self-assembly of helical coordination polymers and formation of a lamellar structure via the cooperativity of two-step Ag(i) coordination and π-π interactions.

Hierarchical self-assembly from a V-shaped ligand 2,9-di(pyridin-4-yl)-1,10-phenanthroline (DPP) to an initial interlocked dimer, further to a coordination polymer with an alternate linear and interlocked helical configuration and finally to a lamellar structure with an undulating surface was precisely achieved in sequence via the cooperativity of two-step Ag (i) coordination and π-π interactions for the first time.

Rotation of a helical coordination polymer by mechanical grinding.

Anisotropic cell volume expansion by mechanical grinding of the solid facilitates the concerted rotation of the photo-inert helical coordination polymer, which causes the misaligned arms containing olefin functional groups in the neighbouring strands to align to undergo [2+2] cycloaddition reaction in 83% yield.

Structural characterization and biological properties of silver(I) tris(pyrazolyl)methane sulfonate

The water-soluble 1D helical coordination polymer [Ag(Tpms)]n (1) [Tpms = tris(pyrazolyl)methane sulfonate, −O3SC(pz)3; pz = pyrazolyl] was synthesized and fully characterized, its single-crystal X-ray diffraction analysis revealing the ligand acting as a bridging chelate N3-donor ligand. The antiproliferative potential of 1 was performed on two human tumour cell lines, A2780 and HCT116, and in normal fibroblasts, with a much higher effect in the former cell line (IC50 of 0.04 μM) as compared to the latter cell line and to normal fibroblasts. Compound 1 does not alter cell cycle progression but interferes with the adherence of A2780 cells triggering cell apoptosis. Apoptosis appears to occur via the extrinsic pathway (no changes in mitochondria membrane potential, reactive oxygen species (ROS) and pro-apoptotic (B-cell lymphoma 2 (BCL-2) associated protein (BAX))/anti-apoptotic (BCL-2) ratio) being this hypothesis also supported by the presence of silver mainly in the supernatants of A2780 cells. Results also indicated that cell death via autophagy was triggered. Proteomic analysis allowed us to confirm that compound 1 is able to induce a stress response in A2780 cells that is related with its antiproliferative activity and the trigger of apoptosis.