Rectangular Macrocycles Research Articles

Size-Induced Highly Selective Synthesis of Organometallic Rectangular Macrocycles and Heterometallic Cage Based on Half-Sandwich Rhodium Building Block.

The controlled synthesis of organometallic supramolecular macrocycles cages remains interesting and challenging work in the field of supramolecular chemistry. Here, two tetranuclear rectangular macrocycles and an octuclear cage were designed and synthesized utilizing a rigid and functionalized pillar linker, 2,6-bis(pyridin-4-yl)-1,7-dihydrobenzo [1,2-d:4,5-d′]diimidazole (BBI4PY) based on three half-sandwich rhodium building blocks bearing different sizes. X-ray crystallography in combination with 1H NMR spectroscopy elucidated that the two building blocks with shorter spacers only result in rectangular macrocycles. However, the building block of bulkier size to avoid the π-π stacking interactions between two ligands BBI4PY led to the formation of an octuclear cage complex. The latter cage contains two types of metal ions, namely Rh3+ and Cu2+, showing significant characteristics of heterogeneous metal-assembling compounds. In addition, the cage accommodates two free isopropyl ether solvent molecules, thus displaying host–guest behavior.

Self-assembled ruthenium (II) metallacycles and metallacages with imidazole-based ligands and their in vitro anticancer activity.

Six tetranuclear rectangular metallacycles were synthesized via the [2+2] coordination-driven self-assembly of imidazole-based ditopic donor 1,4-bis(imidazole-1-yl)benzene and 1,3-bis(imidazol-1-yl)benzene, with dinuclear half-sandwich p-cymene ruthenium(II) acceptors [Ru2(µ-η4-oxalato)(η6-p-cymene)2](SO3CF3)2, [Ru2(µ-η4-2,5-dioxido-1,4-benzoquinonato)(η6-p-cymene)2](SO3CF3)2 and [Ru2(µ-η4-5,8-dioxido-1,4-naphtoquinonato)(η6-p-cymene)2](SO3CF3)2, respectively. Likewise, three hexanuclear trigonal prismatic metallacages were prepared via the [2+3] self-assembly of tritopic donor of 1,3,5-tri(1H-imidazol-1-yl)benzene with these ruthenium(II) acceptors respectively. Self-selection of the single symmetrical and stable metallacycle and cage was observed although there is the possibility of forming different conformational isomeric products due to different binding modes of these imidazole-based donors. The self-assembled macrocycles and cage containing the 5,8-dioxido-1,4-naphtoquinonato (donq) spacer exhibited good anticancer activity on all tested cancer cell lines (HCT-116, MDA-MB-231, MCF-7, HeLa, A549, and HepG-2), and showed decreased cytotoxicities in HBE and THLE-2 normal cells. The effect of Ru and imidazole moiety of these assemblies on the anticancer activity was discussed. The study of binding ability of these donq-based Ru assemblies with ctDNA indicated that the complex 9 with 180° linear 1 ligand has the highest bonding constant Kb to ctDNA.

Controllable assembly of rectangular macrocycles bearing different numbers of unsaturated sites based on half-sandwich iridium fragments.

A series of hexanuclear rectangular macrocycles were designed and synthesized by utilizing multifunctional pyrazine-derived (pyrazine-2,3-diamine (H4L1)) and quinoxaline-derived ligands (2,3-dihydroxy-quinoxaline (H2L2)) featuring two monodentate sites and one pair of chelating sites. X-ray crystallography in combination with 1H NMR spectroscopy elucidated that both half-sandwich iridium diimine and dihydroxy moieties are located on either side of the rectangular macrocycles, making them centrosymmetric. Thereby, the prepared diimine-functionalised complexes were found to have unsaturated metal sites on account of their strongly bound Ir-N-C-C-N arrangement. However, all the iridium atoms in the rectangular macrocycles containing dihydroxy groups were found to adopt an 18-electron coordination configuration, indicating that the O,O'-bonded iridium centers had bound additional ligands, such as Cl-, MeOH, MeCN, etc. Notably, a rare rectangular macrocycle containing a single coordinatively unsaturated metal site was achieved when the ligands H2L12- and L22- were introduced simultaneously.

Syntheses and structural characterization of tetranuclear organometallic macrocycles based on bent connector

4-Amino-3,5-bis(4-pyridyl)-1,2,4-triazole (4-abpt) as bent bridging ligand has been utilized to construct half-sandwich tetranuclear organometallic complexes, namely [Cp*4M4(C2O4)2(4-abpt)2](OTf)4 (M = Rh(1); Ir(2)) and [Cp*4M4(bibzIm)2(4-abpt)2](OTf)4 (M = Rh(3); Ir(4)). Single-crystal X-ray diffraction structural analysis combined with 1H NMR spectra reveal that complexes 1–4 show rectangular macrocycles, in which half-sandwich binuclear units are interlinked by 4-abpt ligands that have relatively flexible angle changes. For macrocycles 1–3, they all feature an anti-arrangement of 4-abpt ligands; However, 4-abpt ligands adopt a syn-arrangement in macrocycle 4.

Discrete Rectangles, Prisms, and Heterometallic Cages from a Conjugated Cp*Rh-Based Building Block

By carefully selecting an existing synthetic strategy and suitable coordination subunits, constructing desired coordination geometries is no longer that difficult to accomplish. Herein, a new strategy to construct a series of unprecedented structures by using conjugated Cp*Rh-based complex BN-OTf (Cp* = η(5)-C5Me5) as the building block is proposed. DFT calculations revealed extensive delocalized π bonds in the subunit. With BN-OTf, rectangular macrocycles TN-bpy and TN-bpe were controllably synthesized. Single-crystal XRD studies confirmed one-dimensional stacking channels for the tetranuclear structure. Notably, the starting ligand imidazole-4,5-dicarboxylate was found to act not only as a tetradentate but also as a hexadentate ligand that can coordinate to further metal ions. Subsequently, [4 Rh+1 M] heterometallic complexes HMZ (M = Cu and Zn) were accessed by chelating borderline hard/soft Lewis acids. With TN-Linker or HMZ, two routes resulted in the [8 Rh+2 M] heterometallic cages HMC (M = Cu and Zn) with excellent crystallinity and stability. Surprisingly, when BN-OTf bonded to rhodium itself, triangular prisms TP-Linker were obtained with high solubility after being linked by bipyridine linkers. Both the X-ray structure and (1)H NMR spectrum confirmed the novel isomerization of the triangular structures. All of the compounds were obtained in high yields and were fully characterized by (1)H NMR spectroscopy, elemental analysis, IR spectroscopy, and in most cases single-crystal X-ray structure determination.

Palladium-free synthesis of [10]cycloparaphenylene

A palladium-free, short-step synthesis of [10]cycloparaphenylene ([10]CPP) has been developed. The key macrocyclization step was performed by a nickel-mediated homocoupling of a newly designed U-shaped unit 2. Surprisingly, the rectangular macrocycle 3 was obtained in high yield compared with previous macrocyclization reactions in CPP syntheses. X-ray crystallography as well as DFT calculation revealed unstrained structure of the macrocycle 3.

Self-Assembly Synthesis, Structural Features, and Photophysical Properties of Dilanthanide Complexes Derived from a Novel Amide Type Ligand: Energy Transfer from Tb(III) to Eu(III) in a Heterodinuclear Derivative

A novel amide type ligand benzyl-N,N-bis[(2'-furfurylaminoformyl)phenoxyl)ethyl]-amine (L) has been designed and applied for the self-assembly generation of homodinuclear lanthanide coordination compounds [Ln2(μ2-L)2(NO3)6(EtOH)2] [Ln = Eu (1), Tb (2), and Gd (3)] and a heterodinuclear derivative [EuTb(μ2-L)2(NO3)6(EtOH)2] (4). All the complexes have been characterized by the X-ray single-crystal diffraction analyses. They are isostructural, crystallize in a monoclinic space group P21/c, and form [2 + 2] rectangular macrocycle structures. Compound 4 is the first example of a [2 + 2] rectangular macrocycle heterodinuclear EuTb complex assembled from an amide type ligand. In 4, the discrete 0D dimeric [EuTb(μ2-L)2(NO3)6(EtOH)2] units are extended, via the multiple N-H···O hydrogen bonds, into a 2D supramolecular network that has been topologically classified as a uninodal 4-connected underlying net with the sql [Shubnikov tetragonal plane net] topology. The triplet state ((3)ππ*) of L studied by the Gd(III) complex 3 demonstrated that the ligand beautifully populates Tb(III) emission (Φ = 52%), whereas the corresponding Eu(III) derivative 1 shows weak luminescence efficiency (Φ = 0.7%) because the triplet state of L has a poor match with (5)D1 energy level of Eu(III). Furthermore, the photoluminescent properties of heterodinuclear complex 4 have been compared with those of the analogous homodinuclear compounds. The quantum yield and lifetime measurements prove that energy transfer from Tb(III) to Eu(III) is being achieved, namely, that the Tb(III) center is also acting to sensitize the Eu(III) and enhancing Eu(III) emission in 4.

Bis(benzimidazole)-based ligands-directed the various dimensionality of metal–organic complexes based on carboxylates co-ligands: Syntheses, structures and properties

Four new metal–organic complexes [Co2(bbix)4(2,6-pdc)2]·4H2O (1), [Co(bbbm)1.5(2,6-pdc)]·2H2O (2), [Ni(bbmmb)2(dnba)2(H2O)2] (3) and [Ni(bbbm)1.5(dnba)2(H2O)]·(0.5bbbm)(H2O) (4) (bbix=1,4-bis(benzimidazol-1-ylmethyl)benzene, bbbm=1,1′-(1,4-butanediyl)bis-1H-benzimidazole, bbmmb=4,4′-bis(benzimidazol-1-ylmethyl)biphenyl, 2,6-H2pdc=2,6-pyridinedicarboxylic acid and Hdnba=3,5-dinitrobenzoic acid) constructed from bis(benzimidazole)-based ligands with different flexibility and organic carboxylates co-ligands have been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction analysis. Complex 1 possesses a binuclear Co2(bbix)2 ring. The adjacent binuclear units are packed into a one-dimensional (1D) supramolecular chain through very weak π–π stacking interactions. Complex 2 shows a two-dimensional (2D) 3-connected (63) topology connected by the flexible bbbm ligands. Complex 3 features a discrete mononuclear structure. The adjacent mononuclear units are linked by the H-bond interactions to form a 1D supramolecular chain. Complex 4 exhibits a 1D infinite chain formed by the Ni2(bbbm)2 rectangular macrocycles and bbbm ligands. The results clearly reveal that the flexibility of bis(benzimidazole)-based ligands have a great influence on the dimensionality and final structures of 1–4. The electrochemical and fluorescence properties for 1–4 have been investigated.

Two birds with one stone: Self-assembly of metal–organic coordination complexes with discrete metallamacrocycle and 1D zigzag chain based on a flexible dicarboxylate ligand

To assemble metal–organic coordination complexes, a flexible dicarboxylate ligand, 2,2′-(4,6-dimethyl-5-nitro-1,3-phenylene)bis(methylene)-bis-(sulfanediyl)dibenzoic acid (H 2 L ), has been designed and synthesized. Using the flexible ligand to assemble with copper ions, a mixture of two metal–organic complexes, Cu 2 ( L ) 2 (py) 4 ·4dmso ( 1 ) and Cu 2 ( L ) 2 (py) 6 ·3dmso·py ( 2 ), has been generated by solvothermal technology in one glass tube. Through increasing the mole fraction of pyridine, the pure phase of complex 2 was obtained. Both complexes have been characterized by single-crystal X-ray diffraction, elemental analysis, and thermogravimetric analysis. Complex 1 is a discrete rectangular macrocycle. The guest solvents of dimethyl sulfoxide molecules were trapped in the cavity of rectangular metallmacrocycle, resulting in the formation of an infinite supramolecular metal–organic nanotube through van der Waals interactions between the guests and the host molecules. In complex 2 , the flexible ligand adopts a syn conformation to assemble with copper ions to form an infinite one-dimensional zigzag chain. The structures of the two complexes vary from discrete metallamacrocycle to 1D zigzag chain with the flexible ligands that are in the syn conformation and the two complexes were gotten in the same glass tube. Because of the existence of the guest molecular, the metal-organic supramolecular nanotubes were formed. ► Two new copper(II) coordination complexes based on a flexible dicarboxylate ligand were synthesized and characterized. ► The flexible ligands in the syn conformation assembled with Cu (II) generated discrete macrometallocycles and 1D zigzag chain subunits in the same glass tube. ► And through increased the mole fraction of pyridine, the pure phase of complex 2 was obtained. ► The metal-organic supramolecular nanotubes were formed because of the existence of the guest molecular.

Anions make the difference: conversion from zero- to one-dimensional structures and luminescent properties of lanthanide-based complexes

Reaction of a newly designed amide type ligand, benzyl-N,N-bis[(2′-benzylaminofomyl)phenoxyl)ethyl]-amine (L) with lanthanide nitrates and picrates has produced two isostructural series of lanthanide coordination compounds, [Ln2L2(NO3)6(DMF)2]n [series 1, monoclinic P21/c, Ln = Pr (1), Sm (2), Eu (3), Tb (4), and Dy (5)] and [LnL(pic)3(CH3CH2OH)]n [series 2, triclinic P, Ln = Nd (6), Eu (7), Tb (8), and Er (9)]. Series 1 have zero-dimensional (0D) dinuclear rectangular macrocycle architectures, while series 2 exhibit one-dimensional (1D) chain patterns. Meanwhile, the two series of structures are further connected through weak intermolecular hydrogen bonds to yield three-dimensional (3D) supramolecular structures. The variations from zero- to one-dimensional coordination structures are attributed to different steric confinement of the nitrate and picrate anions. In addition, we have studied the luminescent properties of the nitrate and picrate complexes, and found that the picrate complexes give very weak luminescence due to coordinated ethanol molecules existing in complexes, which decrease the luminescence. So, herein the luminescent properties of only the Sm (2), Eu (3), Tb (4), and Dy (5) nitrate complexes are investigated in detail.

2+2] Photodimerization in the Solid State Aided by Molecular Templates of Rectangular Macrocycles Bearing Oxamidato Ligands

A series of binuclear half-sandwich iridium and rhodium complexes bearing oxamidato ligands [Cp*2M2(μ-N,N′-bis(aryl)oxamidato)Cl2] (1a, M = Ir, aryl = Ph; 1b, M = Ir, aryl = C6H4-p-Me; 2a, M = Rh, aryl = Ph; 2b, M = Rh, aryl = C6H4-p-Me) functioned as potential ‘‘organometallic clip’’ linear templates were synthesized by the reactions of the lithium salts of oxamide with [Cp*MCl2]2 (M = Ir or Rh), respectively. Treatment of the binuclear complexes (1a−2b) with trans-1,2-bis(4-pyridyl)ethylene (4,4′-bpe) in the presence of AgOTf (OTf = CF3SO3) gave the corresponding tetranuclear complexes of general formula [Cp*4M4(μ-N,N′-bis(aryl)oxamidato)2(μ-4,4′-bpe)2](OTf)4 (3a, M = Ir, aryl = Ph; 3b, M = Ir, aryl = C6H4-p-Me; 4a, M = Rh, aryl = Ph; 4b, M = Rh, aryl = C6H4-p-Me) in high yields. Confirmed by the single-crystal X-ray analysis, the molecular structures of tetranuclear complexes 3a and 4a showed that two binuclear fragments as building blocks were connected by μ-4,4′-bpe to construct a rectangular cavity with the dimensions 5.58 × 13.59 Å (3a) and 5.55 × 13.65 Å (4a). The two μ-4,4′-bpe ligands in 3a and 4a are close to each other within 4.2 Å to allow the [2+2] photoreaction in the solid state, which was proved by 1H NMR of the resulting products (5a−6b′) and single-crystal X-ray analysis.

Self-Assembly of Metal−Organic Supramolecules: From a Metallamacrocycle and a Metal−Organic Coordination Cage to 1D or 2D Coordination Polymers Based on Flexible Dicarboxylate Ligands

To assemble metal-organic supramolecules such as a metallamacrocycle and metal-organic coordination cage (MOCC), a series of flexible dicarboxylate ligands with the appropriate angle, 2,2'-(2,3,5,6-tetramethyl-1,4-phenylene)bis(methylene)bis(sulfanediyl)dibenzoic acid (H(2)L(1)), 2,2'-(2,5-dimethyl-1,4-phenylene)bis(methylene)bis(sulfanediyl)dibenzoic acid (H(2)L(2)), 2,2'-(2,4,6-trimethyl-1,3-phenylene)bis(methylene)bis(sulfanediyl)dinicotinic acid (H(2)L(3)), and 2,2'-(2,4,6-trimethyl-1,3-phenylene)bis(methylene)bis(sulfanediyl)dibenzoic acid (H(2)L(4)), have been designed and synthesized. Using these flexible ligands to assemble with metal ions, six metal-organic supramolecules, Cd(2)(L(1))(2)(dmf)(4)(H(2)O)(2).H(2)O (1), Mn(3)((1)L(2))(2)((2)L(2))(dmf)(2)(H(2)O)(2).5dmf (2), Cu(4)(L(3))(4)(H(2)O)(4).3dmf (3), Cu(4)(L(4))(4)(dmf)(2)(EtOH)(2).8dmf.6H(2)O (4), Mn(4)(L(4))(4)(dmf)(4)(H(2)O)(4).6dmf.H(2)O (5), and Mn(3)(L(4))(3)(dmf)(4).2dmf.3H(2)O (6), possessing a rectangular macrocycle, MOCCs or their extensions, and 1D or 2D coordination polymers, have been isolated. All complexes have been characterized by single-crystal X-ray diffraction, elemental analysis, and thermogravimetric analysis. Complex 1 is a discrete rectangular macrocycle, while complex 2 is a 2D macrocycle-based coordination polymer in which the L(2) ligand adopts both syn and anti conformations. Complexes 3-5 are discrete MOCCs in which two binuclear metal clusters are engaged by four organic ligands. The different geometries of the secondary building units (SBUs) and the axial coordinated solvates on the SBUs result in their different symmetries. Complex 6 is a 1D coordination polymer, extended from a MOCC made up of two metal ions and three L(4) ligands. All of the flexible dicarboxylate ligands adopt a syn conformation except that in complex 2, indicating that the syn conformational ligand is helpful for the formation of a metallamacrocycle and a MOCC. The magnetic properties of complexes 5 and 6 have also been studied.

Supramolecular Architectures of Metal-Containing Macrocycles and a One-Dimensional Supramolecular Structure Based on a Flexible Ligand with an Azobenzene Group

Three new supramolecular structures, [(CuCl)2L2](Cl)2·3H2O (1), [(CuBr)2L2](Br)2·3.5H2O (2), and L·2HClO4 (3), have been prepared by ligand L (L = 2-py-CH2NHOCPhNNPhCONHCH2-py-2, py = pyridine) with CuCl2, CuBr2, and HClO4, respectively. The crystal structures of 1−3 have been determined by single-crystal X-ray diffraction. Both 1 and 2 form interesting [2+2] rectangular macrocycles whose sizes are ca. 15.968 A × 5.345 A and 16.007 A × 5.256 A, respectively. 3 forms a one-dimensional supramolecular structure.

Crystal Engineering Based on Polymeric Hydrogen-Bonded Supramolecules by Self-Assembling of 9, 10-Bis(3,5- dihydroxyphenyl)anthracene and 2,2′,4,4′- Tetrahydroxybenzophenone with Bipyridines

9, 10-bis(3,5-dihydroxyphenyl)anthracene (BDHA) and 2,2′,4,4′-tetrahydroxybenzophenone (THB) are crystallized with bipyridine bases 4,4 ́-bipyridyl(bipy), 1,2-bis(4-pyridyl)ethane (bipy-eta), 1,2-di(4-pyridyl)ethylene (dipy-ete), 1,3-di(4-pyridyl)propane (dipy-pra), 4,4 ́-dipyridyl sulfide (dipy-sul), and 4,4 ́-dipyridyl disulfide(dipy-dis) to afford molecular complexes (BDHA)·(bipy)2 1, (BDHA)·(bipy-eta)2 2,(BDHA)0.5·(dipy-pra)·CH3CH2OH 3, (BDHA)0.5·(dipy-sul)·H2O 4, (BDHA)0.5·(dipy-dis)·CH3CH2OH 5 and (THB)·(dipy-ete)2·H2O 6. The crystal structures of 1–6 have beendetermined by single-crystal X-ray diffraction. All these molecular complexes exhibitpolymeric supramolecular structures via O–H···N or O–H···O hydrogen-bonding. 1 and 2form infinitely rectangular macrocycles linked with one another, whose sizes are ca.12.477 å× 4.802 å and ca.14.575 å × 4.809 å, respectively. 3, 5 and 6 form the one-dimensionalzigzag chain structure. 4 forms a ladder structure, and two dipy-sul molecules were includedin a frame.

Self‐Assembly of Bis(pyrrol‐2‐ylmethyleneamine) Ligands with CuII Controlled by Bridging [−(CH2)n−] Spacers and Weak Intermolecular C−H···Cu Hydrogen Bonding

AbstractBis(pyrrol‐2‐ylmetyhleneamine) ligands linked by alkyl spacers between the imine nitrogens are shown to give dinuclear dimers or mononuclear monomers, depending on the length of the alkyl linker, upon coordination with CuII. Ligands containing ethylene or hexylene linkers −(CH2)n− (n = 2, 6) give dinuclear dimers 5 and 8, while propylene and butylene chains (n = 3, 4) give mononuclear monomers 6 and 7. X‐ray crystal structural analysis reveals that 5 exists as two very similar isomers 5a and 5b, in which the two ligands are bound to two CuII centers to form a distorted helical conformation. In the unit cells of 8, two entirely different isomers 8a and 8b are found. In 8a two ligands are side‐by‐side bound to two CuII centers to form a rectangular macrocycle, while in 8b they are bonded to two CuII centers to form a distorted double‐stranded helix. Moreover, X‐ray structural analysis reveals that complexes 5−8 are further assembled into one‐dimensional polymers through weak, intermolecular C−H···Cu hydrogen bonding, which plays a crucial role in stabilizing the crystal lattice. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)