A brief review of structural concepts of novel supramolecular proton transfer compounds and their metal complexes (part II)

In continuation of our previous brief review of structural concepts of novel supramolecular proton transfer compounds and their metal complexes by Aghabozorg et al. [1], we briefly surveyed the current research in the field of proton transfer compounds supramolecular synthons and their self-assembled metallic complexes from the points of view of Crystal Engineering and Density Functional Theory (DFT) since 2008. Our research groups have recently focused on the proton delivery from acids, which are considered to be suitable proton donors, to amines as proton acceptors. The results were the production of several proton transfer ion pairs possessing some remaining donor sites applied for coordination to metal centers in the preparation of metal-organic compounds. Some of the complexes showed contributions of both cationic and anionic fragments of the starting ion pair, while some others contained only one of these species as ligand. Our review and investigation of compounds revealed that they mainly focused on the concept of supramolecular systems, co-crystallization, stereochemically active lone pairs, coordination polyhedron, mainly on the various interactions involved, including van der Waals, ion pairing, hydrogen bondings, face to face ??-?? stackings and edge to face C-H???, C-O???, N-H3?? and S?S. These interactions were the most commonly used strategies in the extension of supramolecular structures.     

苯甲酸与含氮配体构筑的两种铅配合物的水热合成、结构与性质研究

用水热合成方法得到了2个二价铅配合物[Pb(BA)2(phen)].(HBA)(1)及[Pb(2,2′-bipy)(BA)(NO3)]n(2)(HBA=benzoic acid;phen=1,10-phenanthroline;2,2′-bipy=2,2′-bipyridine),对它们进行了元素分析、红外光谱、荧光光谱、粉晶衍射及热分析表征,并通过X-射线单晶衍射测定了配合物的单晶结构。X-射线单晶结构解析表明,配合物1与2均属三斜晶系,P1空间群。化合物1中,弱Pb…O相互作用、分子间氢键及π…π堆积作用共同构筑了配合物1的三维框架结构。铅的6s孤电子具有立体化学活性,使配位键分布于半球型区域。化合物2中,相邻的PbⅡ离子通过螯合-桥联的硝酸根联结成一维链状结构,广泛存在的π…π堆积作用将邻近的一维链堆积成三维超分子结构。化合物2中的6s孤对电子未显示出立体化学活性,其配位键近似分布于全球型区域。     

Supramolecular Paradigm for Capture and Co-Precipitation of Gold(III) Coordination Complexes

A new supramolecular paradigm is presented for reliable capture and co-precipitation of haloauric acids (HAuX₄) from organic solvents or water. Two classes of acyclic organic compounds act as complementary receptors (tectons) by forming two sets of directional non-covalent interactions, (a) hydrogen bonding between amide (or amidinium) NH residues and the electronegative X ligands on the AuX₄⁻, and (b) electrostatic stacking of the electron deficient Au center against the face of an aromatic surface. X-ray diffraction analysis of four co-crystal structures reveals the additional common feature of proton bridged carbonyls as a new and predictable supramolecular design element that creates one-dimensional polymers linked by very short hydrogen bonds (CO⋅⋅⋅OC distance <2.5 Å). Two other co-crystal structures show that the amidinium-π⋅⋅⋅XAu interaction will reliably engage AuX₄⁻ with high directionality. These acyclic compounds are very attractive as co-precipitation agents within new “green” gold recovery processes. They also have high potential as tectons for controlled self-assembly or co-crystal engineering of haloaurate composites. More generally, the supramolecular paradigm will facilitate the design of next-generation receptors or tectons with high affinity for precious metal square planar coordination complexes for use in advanced materials, nanotechnology, or medicine.     

Putting anion-π interactions into perspective

Supramolecular chemistry is a field of scientific exploration that probes the relationship between molecular structure and function. It is the chemistry of the noncovalent bond, which forms the basis of highly specific recognition, transport, and regulation events that actuate biological processes. The classic design principles of supramolecular chemistry include strong, directional interactions like hydrogen bonding, halogen bonding, and cation-π complexation, as well as less directional forces like ion pairing, π-π, solvophobic, and van der Waals potentials. In recent years, the anion-π interaction (an attractive force between an electron-deficient aromatic π system and an anion) has been recognized as a hitherto unexplored noncovalent bond, the nature of which has been interpreted through both experimental and theoretical investigations. The design of selective anion receptors and channels based on this interaction represent important advances in the field of supramolecular chemistry. The objectives of this Review are 1) to discuss current thinking on the nature of this interaction, 2) to survey key experimental work in which anion-π bonding is demonstrated, and 3) to provide insights into the directional nature of anion-π contact in X-ray crystal structures.     

[60]富勒烯的超分子自组装研究进展

超分子自组装是发展超分子电子学的重要途径。随着纳米科学和技术的迅速发展,自组装技术已成功地应用于纳米尺度物质的维数、形貌和功能等的调控。作为构筑分子水平上一维、二维、三维有序功能结构和高有序分子聚集态结构的关键技术,超分子自组装技术有力地推动了具有优良光、电、磁性能的分子材料和纳米功能材料更深层次的研究。本文综述了超分子自组装在富勒烯科学领域的基础研究和应用,特别是对有利于自组织和自组装功能的富勒烯基衍生物的设计与合成、超分子作用力引导的具有特定结构的分子体系的可控自组装、以及富勒烯分子聚集态结构材料的光物理过程、超分子中电子转移和能量转移现象进行了描述;并对卟啉、四硫富瓦烯、碗烯和杯芳烃等一系列富π电子化合物和大环主体分子等包含[60]富勒烯的主体化合物的超分子作用和超分自组装体以及通过氢键、π-π作用、静电力和范德华力和金属配位作用形成的[60]富勒烯超分子自组装体进行了总结,对未来发展进行了展望。     

Supramolecular architecture of crystals of perfluorinated 3-alkylphthalides

The molecular and crystal structures of perfluoro-3-alkylphthalides (3-hydroxyperfluoro-3-methylphthalide and its hydrate, two polymorphs of 3-hydroxyperfluoro-3-ethylphthalide and 3-hydroxyperfluoro-3-isopropylphthalide) are determined by single crystal X-ray diffraction. In the crystals, the supramolecular O–Н…O=C synthon occurs leading, except the crystallohydrate, to the formation of C₁¹ (6) hydrogen bonded chains (supramolecular 1D motifs). According to the DFT/M06-2X/TZV calculations, the interaction energy of hydrogen bonded molecular pairs increases in this series, which can be explained by additional C=O…π, O…π, and C–F…π interactions.     

Lone pair···π interactions on the stabilization of intra and intermolecular arrangements of coordination compounds with 2-methyl imidazole and benzimidazole derivatives

Abstract

Spectroscopic and single crystal X-ray diffraction studies of coordination compounds of Co^II, Ni^II, Zn^II, and Pd^II with phenylsulfonyl imidazole and benzimidazole derivatives (2-mfsiz, 2-mfsbz) were performed. The relevance of non-covalent interactions on the stabilization of intra and intermolecular arrangements in the ligands and their coordination compounds was investigated. The imidazole 2-mfsiz ligand presents two enantiomeric conformers, where the ethylphenylsulfone moiety stabilizes intermolecular lone pair···π (S–O···π_(phe)) and H···π contacts, while its tetrahedral coordination compounds, [M(2-mfsiz)₂X₂] (M²⁺?=?Co, Ni, Zn; X?=?Cl, Br) showed intramolecular lone pair···π interactions (S–O···π_(iz)). On the other hand, compounds [Cu₂(2-mfsiz)₂(µ₂-AcO)₄] and trans-[Pd(2-mfsiz)₂Cl₂] do not present lone pair···π interactions due to the metal ion geometry (square base pyramidal or square planar), which leads to formation of π_(iz)···π_(phe) interactions. For the benzimidazole ligand 2-mfsbz, an intramolecular, H_(phe)···π_(bz) contact was observed, remaining in its tetrahedral and octahedral coordination compounds, [M(2-mfsbz)₂X₂] (M²⁺?=?Co, Zn; X?=?Cl, Br, NO₃). This interaction limits the free rotation of the ethylphenylsulfone moiety for stabilization of an intermolecular lone pair···π interaction (S–O···π_(iz)). The dimeric [Zn₂(2-mfsiz)₂(µ²-AcO)₄] compound has a π_(bz)···π_(phe) contact. Theoretical calculations confirmed the non-covalent interactions in the ligands and their coordination compounds.     

Host-guest supramolecular interactions in the coordination compounds of 4,4'-azobis(pyridine) with MnX2 (X = NCS–, NCNCN–, and PF6(–)): structural analyses and theoretical study

Three new Mn(II) coordination compounds {[Mn(NCNCN)(2)(azpy)]·0.5azpy}(n) (1), {[Mn(NCS)(2)(azpy)(CH(3)OH)(2)]·azpy}(n) (2), and [Mn(azpy)(2)(H(2)O)(4)][Mn(azpy)(H(2)O)(5)]·4PF(6)·H(2)O·5.5azpy (3) (where azpy = 4,4'-azobis(pyridine)) have been synthesized by self-assembly of the primary ligands, dicyanamide, thiocyanate, and hexafluorophosphate, respectively, together with azpy as the secondary spacer. All three complexes were characterized by elemental analyses, IR spectroscopy, thermal analyses, and single crystal X-ray crystallography. The structural analyses reveal that complex 1 forms a two-dimensional (2D) grid sheet motif. These sheets assemble to form a microporous framework that incorporates coordination-free azpy by host-guest π···π and C-H···N hydrogen bonding interactions. Complex 2 features azpy bridged one-dimensional (1D) chains of centrosymmetric [Mn(NCS)(2)(CH (3)OH)(2)] units which form a 2D porous sheet via a CH(3)···π supramolecular interaction. A guest azpy molecule is incorporated within the pores by strong H-bonding interactions. Complex 3 affords a 0-D motif with two monomeric Mn(II) units in the asymmetric unit. There exist π···π, anion···π, and strong hydrogen bonding interactions between the azpy, water, and the anions. Density functional theory (DFT) calculations, at the M06/6-31+G* level of theory, are used to characterize a great variety of interactions that explicitly show the importance of host-guest supramolecular interactions for the stabilization of coordination compounds and creation of the fascinating three-dimensional (3D) architecture of the title compounds.     

Anion-(π)n-π Catalytic Micelles

Anion-π catalysis operates by stabilizing anionic transition states on π-acidic aromatic surfaces. In anion-(π)_n-π catalysis, π stacks add polarizability to strengthen interactions. In search of synthetic methods to extend π stacks beyond the limits of foldamers, the self-assembly of micelles from amphiphilic naphthalenediimides (NDIs) is introduced. To interface substrates and catalysts, charge-transfer complexes with dialkoxynaphthalenes (DANs), a classic in supramolecular chemistry, are installed. In π-stacked micelles, the rates of bioinspired ether cyclizations exceed rates on monomers in organic solvents by far. This is particularly impressive considering that anion-π catalysis in water has been elusive so far. Increasing rates with increasing π acidity of the micelles evince operational anion-(π)_n-π catalysis. At maximal π acidity, autocatalytic behavior emerges. Dependence on position and order in confined micellar space promises access to emergent properties. Anion-(π)_n-π catalytic micelles in water thus expand supramolecular systems catalysis accessible with anion-π interactions with an inspiring topic of general interest and great perspectives.     

Research Progress of Regulation of Driving Forces in Short Peptide Supramolecular Self-Assembly北大核心CSCD

Some short peptides can spontaneously self-assemble into various nanostructures via the synergistic driving forces of non-covalent interactions. These non-covalent interactions,including electrostatic interaction,hydrogen bonding,aromatic interactions and other non-covalent interactions,are usually highly coupled together. Through rational sequence design and proper modification of short peptide molecules,the driving forces could be regulated purposively,and the nanostructures and morphologies of the self-assemblies could be controlled accordingly,and thus so as to achieve the fabrication of peptide-based supramolecular biomaterials and develop their functions. In this paper,the effects of hydrogen bonding,π-π stacking, electrostatic interaction,hydrophobic interaction,metal ion coordination and chiral center on the self-assembly behavior of peptide self-assembly have been reviewed. The driving force regulation strategies, including sequence design,pH and concentration adjustment and metal ion coordination,and the resulted nanostructures have also been discussed. We also make the outlooks on the development of peptide-based supramolecular biomaterials with specific functions in biomedicines and biocatalysis. © 2022, Science Press (China). All rights reserved.     

Thallium(I) supramolecular compounds: Structural and properties consideration

During the last two decades, supramolecular compounds and especially coordination polymers have received great attention and the number of their synthesized compounds is still growing, which is mainly due to their potential application in various fields such as microelectronics, nonlinear optics, ion exchange, catalysis, gas storage, separation and luminescence. Formation of polymers with main group metal ions such as thallium(I) is disproportionately sparse when compared with those of other metals. Because of the interest structures, properties and applications of thallium polymers, it is necessary to understand thallium's ability to bind donors and form supramolecular compounds. This review tries to give an overview of all supramolecular compounds which were reported from thallium(I) after 1990 and to investigate their properties and applications. Thallium(I) usually forms neutral species and exhibits greater tendency to forming one-dimensional supramolecular compounds. Thallium(I) also favors secondary interactions on its coordination sphere (especially with unsaturated carbon atoms forms organometallic polymers) with stereochemically active lone pair and hemidirected coordination sphere around it.     

Two supramolecular complexes of gallium(III) with different adduct ion pairs containing pyridine-2,6-dicarboxylic acid: Syntheses,characterization, crystal structures and computational study

Two complexes of gallium(III) with adduct ion pair compounds containing pyridine-2,6-dicarboxylic acid and two different Lewis bases are synthesized. The chemical formulae are (dmpH)[Ga(pydc)₂]·2H₂O, (1) and (bpyH₂)_1/2(pydcH₂)_1/2[Ga(pydc)₂]·4H₂O, (2) where pydc, dmp, and bpy are pyridine-2,6-dicarboxylate, 2,9-dimethyl-1,10-phenanthroline, and 4,4′-bipyridine respectively. The two crystal structures illustrate that the Ga^III ion is six-coordinated by two pyridine-2,6-dicarboxylates. Hydrogen bonds as well as other noncovalent interactions such as ion-pairing, C-O...π, C-H...π, and π...π stacking play an important role in the formation of supramolecular systems. Particular attention is given to the molecular geometries and NMR properties of the complexes from the computational point of view. The electronic properties of the complexes are analysed using the parameters derived from the atoms in molecules (AIM) and natural bond orbital (NBO) methodologies at the B3LYP/6-311++G(2d,2p) computational level.     

Supramolecular interaction patterns in the zinc(II) dichloride and tin(IV) tetrachloride complexes with dipyrido[f,h]quinoxaline‐6,7‐dicarbonitrile

This study characterizes the supramolecular synthons that dominate the intermolecular organization of the title compounds, namely dichloridobis(dipyrido[f,h]quinoxaline‐6,7‐dicarbonitrile)zinc(II), [ZnCl₂(C₁₆H₆N₆)₂], (I), and tetrachlorido(dipyrido[f,h]quinoxaline‐6,7‐dicarbonitrile)tin(IV), [SnCl₄(C₁₆H₆N₆)], (II), in their respective crystal structures. Molecules of (I) are located on 2^b axes of rotational symmetry. Their crystal packing is stabilized mostly by π–π stacking and dipole–dipole attractions between the organic ligand fragments of inversion‐related neighbouring species, as well as by weak intermolecular C—H...N hydrogen bonds. On the other hand, Cl...π and N...π interactions seem to direct the crystal packing in (II), which is unusual in the sense that its aromatic fragments are not involved in π–π stacking. Molecules of (II) are located on m^b planes of mirror symmetry. This study confirms the diverse structural chemistry of this organic ligand, which can be involved in a wide range of supramolecular interactions. These include effective coordination to various metal ions via the phenathroline N‐atom sites, π–π stacking and π...halogen contacts through its extended π‐system, and hydrogen bonding and N...π interactions through its nitrile groups. The competing natures of the latter make it difficult to predict a priori the preferred supramolecular motif that may form in a given structure.     

LCAO-MO-SCF-Calculations on the stability and Sterochernistry of hydrogen bonds

CNDO and INDO calculations were performed on numerous structures with hydrogen bonds of different strength. An almost linear relationship is found between the strength of weak hydrogen bonds and the amount of charge transfered.π-electrons and lone pairs are nearly equivalent in hydrogen bonding. The stereochemistry of hydrogen bonds is determined largely by additional interactions betweenσ-bonds of the two molecules. Since proton affinities are calculated too large by the CNDO method, an error is introduced in the potential curves for proton transfer in weak hydrogen bonds. In systems with strong hydrogen bonds both structures with the proton on the right and left have almost the same energy and hence the potential curves for proton transfer are free of the errors mentioned above.     

Induction-driven stabilization of the anion-π interaction in electron-rich aromatics as the key to fluoride inclusion in imidazolium-cage receptors

Intermolecular interactions that involve aromatic rings are key processes in both chemical and biological recognition. It is common knowledge that the existence of anion-π interactions between anions and electron-deficient (π-acidic) aromatics indicates that electron-rich (π-basic) aromatics are expected to be repulsive to anions due to their electron-donating character. Here we report the first concrete theoretical and experimental evidence of the anion-π interaction between electron-rich alkylbenzene rings and a fluoride ion in CH(3)CN. The cyclophane cavity bridged with three naphthoimidazolium groups selectively complexes a fluoride ion by means of a combination of anion-π interactions and (C-H)(+)···F(-)-type ionic hydrogen bonds. (1)H NMR, (19)F NMR, and fluorescence spectra of 1 and 2 with fluoride ions are examined to show that only 2 can host a fluoride ion in the cavity between two alkylbenzene rings to form a sandwich complex. In addition, the cage compounds can serve as highly selective and ratiometric fluorescent sensors for a fluoride ion. With the addition of 1 equiv of F(-), a strongly increased fluorescence emission centered at 385 nm appears at the expense of the fluorescence emission of 2 centered at 474 nm. Finally, isothermal titration calorimetry (ITC) experiments were performed to obtain the binding constants of the compounds 1 and 2 with F(-) as well as Gibbs free energy. The 2-F(-) complex is more stable than the 1-F(-) complex by 1.87 kcal mol(-1), which is attributable to the stronger anion-π interaction between F(-) and triethylbenzene.     

Identity hydride-ion transfer from C-H donors to C acceptor sites. Enthalpies of hydride addition and enthalpies of activation. Comparison with C...H...C proton transfer. An ab initio study

Enthalpies of addition of hydride ion to eleven carbonyl acceptors (X-CHO), two conjugate addition sites (X-CH=CH2; X = CHO, NO2), eight carbenium ion acceptors, fulvene, borane, and SiH3(+) were calculated at the MP2/6-311+G level. Correlation between calculated and experimental enthalpies of addition of hydride ion is excellent. Transition states (ts) for the identity hydride transfers between the acceptors and their corresponding hydride adducts (hydride donors) were also calculated. The carbonyl and fulvene reactions have transition states with one imaginary frequency: the hydrogen transfer coordinate. The carbenium ions, borane, and SiH3(+) gave not transition states but stable compounds upon addition of the hydride donor. Computational differences between these hydride transfers and previously reported proton transfers include shorter partial C...H bonds and a tendency toward bent C...H...C angles for the hydride transfer ts and addition compound structures, particularly when a bent geometry improves interactions elsewhere in the structure. These and other differences are explained by modeling the hydride transfer ts and addition compounds as two-electron, three-center systems involving the transfer termini and the shared hydrogen but the proton transfer ts structures as four-electron, three-center systems. Charge and geometry measures suggest transition states in which these features change synchronously, again in contrast to many proton transfer reactions. For the X-CHO set, polar effects dominate enthalpies of hydride addition, with resonance effects also important for resonance donors; these preferentially stabilize the acceptor, reducing its hydride ion affinity. Activation enthalpies are dominated by resonance stabilization of the acceptors, greatly attenuated in the transition states.     

Two-dimensional Supramolecular Polymers Based on Selectively Recognized Aromatic Cation-π and Donor-Acceptor Motifs for Photocatalytic Hydrogen Evolution

Two-dimensional (2D) organic polymers have recently received considerable interest, especially those whose architectures are held together via supramolecular engineering. However, current approaches toward supramolecular 2D structures usually suffer from mutual interference of noncovalent interactions and lack of intrinsic functions. Herein, we report well-regulated 2D supramolecular polymers (2DSPs) through an aromatics-selective recognition strategy of cation-π and donor-acceptor (D-A) motifs, which are derived from C₄-symmetric cationic monomers and electron-withdrawing molecules. By subtly designing the strength and direction of noncovalent driving forces, the mutual interference between cation-π and D-A interactions is effectively avoided, enabling the construction of 2DSPs in aqueous solution. On this basis, the resultant 2DSPs possess boosted photocatalytic hydrogen evolution activity at a rate of 600 μmol g⁻¹ h⁻¹, which is mainly ascribed to the specific stacking mode of cation-π/D-A motifs and the ordered 2D structures.     

Selective hydrolysis of phosphate monoester by a supramolecular phosphatase formed by the self-assembly of a bis(Zn(2+)-cyclen) complex, cyanuric acid, and copper in an aqueous solution (cyclen = 1,4,7,10-tetraazacyclododecane)

In Nature, organized nanoscale structures such as proteins and enzymes are formed in aqueous media via intermolecular interactions between multicomponents. Supramolecular and self-assembling strategies provide versatile methods for the construction of artificial chemical architectures for controlling reaction rates and the specificities of chemical reactions, but most are designed in hydrophobic environments. The preparation of artificial catalysts that have potential in aqueous media mimicking natural enzymes such as hydrolases remains a great challenge in the fields of supramolecular chemistry. Herein, we describe that a dimeric Zn(2+) complex having a 2,2'-bipyridyl linker, cyanuric acid, and a Cu(2+) ion automatically assembles in an aqueous solution to form a 4:4:4 complex, which is stabilized by metal-ligand coordination bonds, π-π-stacking interactions, and hydrogen bonding and contains μ-Cu(2)(OH)(2) cores analogous to the catalytic centers of phosphatase, a dinuclear metalloenzyme. The 4:4:4 complex selectively accelerates the hydrolysis of a phosphate monoester, mono(4-nitrophenyl)phosphate, at neutral pH.     

Supramolecular ligand-ligand and ligand-substrate interactions for highly selective transition metal catalysis

The use of non covalent supramolecular ligand-ligand and ligand-substrate interactions in transition metal-catalysed transformations is a new, rapidly emerging area of research. Non-covalent interactions between monodentate ligands such as hydrogen bonding, coordinative bonding, ion pairing, π-π interactions and the formation of inclusion compounds, have been shown to impart higher activity and chemo-, regio-, and stereoselectivity to the corresponding transition metal complexes in a number of catalytic applications. Analogously, supramolecular ligand-substrate interactions, and particularly hydrogen bonding, have been used to direct the regio- and stereochemistry of several metal-catalysed reactions. The catalytic systems relying on supramolecular interactions are generally capable of self-assembling from simpler components in the environment where catalysis is to take place, and are therefore very well-suited for combinatorial catalyst discovery strategies and high-throughput screening.     

芳环超分子体系中的π-π作用

π-π作用是芳环超分子体系中广泛存在的一种重要的弱相互作用. 本文对π-π作用的特征、形式、有效参数和表征方法等作了比较全面的综述, 同时小结了影响π-π作用的一些重要因素, 最后还概述了近年来π-π作用在超分子组装、不对称催化、有机半导体材料等领域的研究进展.