Macrocyclic Chain Research Articles

Directionality Reversal and Shift of Rotational Axis in a Hemithioindigo Macrocyclic Molecular Motor.

Molecular motors are central driving units for nanomachinery, and control of their directional motions is of fundamental importance for their functions. Light-driven variants use easy to provide, easy to dose, and waste-free fuel with high energy content, making them particularly interesting for applications. Typically, light-driven molecular motors work via rotations around dedicated chemical bonds where the directionality of the rotation is dictated by the steric effects of asymmetry in close vicinity to the rotation axis. In this work, we show how unidirectional rotation around a virtual axis can be realized by reprogramming a molecular motor. To this end, a classical light-driven motor is restricted by macrocyclization, and its intrinsic directional rotation is transformed into a directional rotation of the macrocyclic chain in the opposite direction. Further, solvent polarity changes allow to toggle the function of this molecular machine between a directional motor and a nondirectional photoswitch. In this way, a new concept for the design of molecular motors is delivered together with elaborate control over their motions and functions by simple solvent changes. The possibility of sensing the environmental polarity and correspondingly adjusting the directionality of motions opens up a next level of control and responsiveness to light-driven nanoscopic motors.

Crystal Engineering of Polymeric Structures with Dative Boron–Nitrogen Bonds: Design Criteria and Limitations

A database analysis of known adducts between pyridyl donor ligands and Lewis acidic boronate esters revealed a preference for a particular conformation at the boron centers. On the basis of this analysis, we designed two tritopic pyridyl ligands, which were expected to form polymeric structures upon combination with ditopic bis(benzenedioxaborole) Lewis acids. Instead of two-dimensional networks, we observed the formation of chains of macrocycles for different ester/N-donor combinations. This kind of structural motif is unprecedented for polymeric B–N adducts. The predictability of the chemistry was compromised by the low strength of the dative B–N bond, which resulted in incomplete adduct formation and/or cocrystallization of starting materials.

On the Importance of Noncovalent Carbon-Bonding Interactions in the Stabilization of a 1D Co(II) Polymeric Chain as a Precursor of a Novel 2D Coordination Polymer.

A new cobalt(II) coordination polymer 2 with μ1,5 dicyanamide (dca) and a bidentate ligand 3,5-dimethyl-1-(2'-pyridyl)pyrazole (pypz) is prepared in a stepwise manner using the newly synthesized one-dimensional linear Co(II) coordination polymer 1 as a precursor. The structural and thermal characterizations elucidate that the more stable complex 2 shows a two-dimensional layer structural feature. Here, Co(II) atoms with μ1,5 dicyanamido bridges are linked by the ligand pypz forming a macrocyclic chain that runs along the crystallographic 'c' axis having 'sql' (Shubnikov notation) net topology with a 4-connected uninodal node having point symbol {4(4).6(2)}. The remarkable noncovalent carbon-bonding contacts detected in the X-ray structure of compound 1 are analyzed and characterized by density functional theory calculations and the analysis of electron charge density (atoms in molecules).

Syntheses, structures and properties of nickel(II) and manganese(II) coordination polymers based on V-shaped bis-imidazole and aromatic carboxylate ligands

Using V-shaped mixed ligands bis-imidazole and aromatic carboxylic acids, five new coordination polymers namely, {[Ni(B-im)(Br-a)Cl]·H2O}n (1), {[Ni(B-im)(I-a)(H2O)2]·0.5H2O}n (2), [Ni(B-im)(I-a)(H2O)2]n (3), [Ni(B-im)(M-a)(H2O)2]n (4) and {[Mn2(B-im)2(I-a)2]·2H2O}n (5) [B-im=1,1′-(5-methyl-1,3-phenylene)bis(1H-imidazole), Br-a=5-bromonicotinic acid, I-a=isophthalic acid and M-a=5-methylisophthalic acid] were solvothermally synthesized and fully characterized by IR spectra, element analyses, X-ray powder and single-crystal diffractions, and thermogravimetric analyses. Complexes 1 and 2 feature polymeric macrocyclic chain structures containing interesting nanotubular channels, which are constructed by bridging 30-membered macrocyclic [Ni3(B-im)3] subunits with Br-a ligands and by bridging folded 20-membered macrocyclic [Ni2(B-im)2] subunits with I-a ligands, respectively. Isomorphic complexes 3 and 4 represent double-chain structures containing folded 18-membered macrocyclic [Ni2(B-im)(I-a)] subunits and [Ni2(B-im)(M-a)] subunits, respectively. Complex 5 is a 2D porous coordination polymer containing novel chiral four-stranded Mn(II) chains consisting of two (B-im)-bridged aspiral chiral chains and two (I-a)-bridged heterochiral coaxial 21-helical chains. The results of thermal gravimetric analyses suggest that the dehydrated frameworks of 1–5 are stable up to 320°C. Additionally, the magnetism of complexes 3 and 5 were also investigated.

Insights into bonding interactions and excitation energies of 3d-4f mixed lanthanide transition metal macrocyclic complexes.

In this contribution, a computational study of equatorial bound tetranuclear macrocycle (butylene linked) [LnZn(HOMBu)]3+ (Ln = La3+, Ce3+) complexes was carried out. Here, the electronic structure, bonding interaction and excitation energies were studied within the relativistic density functional theory framework. From the electronic structure analysis, the frontier molecular orbitals (FMOs) were strongly localized in the d-orbitals of the Zn centers and the f-orbitals of the lanthanide ions. Besides, the inner MOs were found to exhibit a π-character from the organic part of the macrocyclic chain. EDA-NOCV was used as a tool for evaluating the bonding interaction, taking the trinuclear metallomacrocycle (ZnHOMBu) and the lanthanide center as fragments. This analysis showed that the interaction between these fragments was slightly covalent; with this covalency being the result of a charge transfer from the metallomacrocyclic ring to the lanthanide. This phenomenon was observed in the deformation density channels obtained from the EDA-NOCV study; in which π- and σ-charge transfer was observed. Finally, the TD-DFT study of the excitation energies evidenced three sets of bands: the first set with the highest intensity represented the ligand to metal charge transfer bands; the second set could be attributed to the 3d-4f electronic transitions between the metal centers; and the third set represented the f-f bands found for the open-shell cerium complex. This class of complexes accomplishes the "antenna effect" principle, which states that highly absorptive transition-metal (TM) complexes can be used to enhance the luminescence of poorly emissive systems, and are introduced in this study as self-sensitizer bimetallic d-f systems with potential applications in near infra-red (NIR) technologies.

Catena-Poly[[[diaquazinc(II)]-bis[μ-2-(2,4-difluorophenyl)-1,3-bis(1,2,4-triazol-1-yl)propan-2-ol-κ2N4:N4]] bis(perchlorate)

The formula unit of the title one-dimensional coordination polymer, {[Zn(C13H12F2N6O)2(H2O)2](ClO4)2}n, which is twice the asymmetric unit, contains a ZnII ion on an inversion centre, two fluconazole [or 2-(2,4-difluoro­phenyl)-1,3-bis­(1,2,4-triazol-1-yl)propan-2-ol] ligands, two water mol­ecules and two perchlorate anions. The fluconazole ligands connect the ZnII atoms through their N4 atoms in a head-to-tail fashion, resulting in the formation of a one-dimensional cationic macrocyclic chain structure. These one-dimensional cationic chains are connected by hydrogen bonds into a two-dimensional layer structure. There is also a π–π supra­molecular inter­action of the benzene rings of the flucanozole ligands between the chains.

Lone-Pair Activity in Lead(II) Complexes with Unsymmetrical Lariat Ethers

We have carried out a study about the structural effect of the lone-pair activity in lead(II) complexes with the unsymmetrical lariat ethers L(7), L(8), (L(8)-H)-, (L(9)-H)-, and (L(10)-H)-. All these ligands are octadentate and differ by the aromatic unit present in their backbones: pyridine, phenol, phenolate, thiophenolate, and pyrrolate, respectively. In these lead(II) complexes, the receptor may adopt two possible syn conformations, depending on the disposition of the pendant arms over the crown moiety fragment. The conformation where the pendant arm holding the imine group is placed above the macrocyclic chain containing two ether oxygen atoms has been denoted as I, whereas the term II refers to the conformation in which such pendant arm is placed above the macrocyclic chain containing the single oxygen atom. Compounds of formula [Pb(L(7))](ClO4)2 (1) and [Pb(L(8)-H)](ClO4) (2) were isolated and structurally characterized by X-ray diffraction analyses. The crystal structure of 1 adopts conformation I and shows the lead(II) ion bound to the eight available donor atoms of the bibracchial lariat ether in a holodirected geometry, whereas the geometry of 2 is best described as hemidirected, with the receptor adopting conformation II. The five systems [Pb(L(7))]2+, [Pb(L(8))]2+, [Pb(L(8)-H)]+, [Pb(L(9)-H)]+, and [Pb(L(10)-H)]+ were characterized by means of density functional theory calculations (DFT) performed by using the B3LYP model. An analysis of the natural bond orbitals (NBOs) indicates that the Pb(II) lone-pair orbital remains almost entirely s in character in the [Pb(L(7))]2+ complexes, whereas in [Pb(L(8)-H)]+, the Pb(II) lone pair is polarized by a certain 6p contribution. The reasons for the different roles of the Pb(II) lone pair in compounds 1 and 2 as well as in the related model compounds are discussed. Our results point to the presence of a charged donor atom in the ligand (such as a phenolate oxygen atom, pyrrolate nitrogen atom, or even thiophenolate sulfur atom) favoring hemidirected geometries.

Synthesis of new macrobicyclic tricompartmental ligands and site preference of metal ion: structural and electrochemical properties of mononuclear copper(II) complexes

New macrobicyclic tricompartmental ligands and their mononuclear copper(II) complexes of type [CuH 2L](ClO 4) 2 have been synthesized from the precursor compound 3,4:10,11-dibenzo-1,13[ N, N ′{bis(3-formyl-2-hydroxy-5-methyl)benzyl}diaza]-5,9-dioxa-cycloheptadecane with diamines like en, pn and bn by template method. These complexes have been characterized by IR, UV spectral and X-ray studies. Complex [CuH 2L 3](ClO 4) 2 (in L 3 the diamine used is bn) crystallized as triclinic system with space group p-1. The crystal structure explains that the geometry around copper is distorted square planar. Among the three compartments, it is interesting to observe that the metal ion prefers to be encompassed by the compartment containing phenolic oxygens and imine nitrogens (N 2O 2). From X-ray studies the presence of perchlorate anions, acetonitrile solvent molecules and the protonation of tertiary nitrogen atoms were well understood. All the complexes show hyperfine splittings in ESR spectra. The μ eff values observed in the range 1.69–1.72 BM are close to the spin only value of single copper(II) ion. Cyclic voltammetry studies of these complexes depict one electron quasireversible reduction in the range −0.80 to −0.90 V at negative potential. A red shift in UV–Visible spectra and shifting of reduction potential towards anodic in cyclic voltammetry were witnessing the distortion of the geometry around metal center from the planarity as the macrocyclic chain length in imine nitrogen compartment increases.

Diversity of polymeric structures for copper complexes of the extended-reach siloxypyridine ligands [ iPr 2SiO(CH 2) npy] 2O ( n=0, 1, 3)

The structures of six copper(II) complexes formed by the siloxypyridine ligands [ i Pr 2SiO(CH 2) n py] 2O ( n=0, 1, 3), and of a copper(I) iodide complex of ( i Pr 2SiOpy) 2O, have been determined. In all cases polymeric structures are produced, but with a diversity of structural types. Chains of 24-membered macrocycles are present in Cu[( i Pr 2SiOpy) 2O] 2Br 2. The structure of Cu 4[( i Pr 2SiOpy) 2O] 2I 4 also comprises chains of macrocycles but with Cu 4I 4 polyhedra as the connecting ‘node’ points. In [Cu 2(OAc) 4{( i Pr 2SiOCH 2py) 2O}] dinuclear Cu 2(OAc) 4 units are linked into chains by the ( i Pr 2SiOCH 2py) 2O ligands. Chains of 28-membered macrocycles are formed by [Cu{( i Pr 2SiOCH 2py) 2O} 2(H 2O) 2](NO 3) 2, with further cross-linking by hydrogen bonding between the aqua ligands and the nitrate anions. Two crystalline forms of [Cu 2{( i Pr 2SiOCH 2py) 2O} 3Br 4] were obtained, one comprising ‘tapes’ of contiguous 28- and 112-membered macrocycles and the other interpenetrating folded sheets of 84-membered macrocycles. Chains of 36-membered macrocycles are formed by [Cu{( i Pr 2SiOCH 2CH 2CH 2py) 2O} 2(NO 3) 2].

Phosphorus Crown-Ethers with Nitrogen-Containing Heterocycles

Abstract Phosphorus-containing crown-ethers functionalized by heterocycle fragments have essential advantages over the usual ones. The introduction of structural units of indoles, pyrroles and indolizines to phosphorus atom of the macrocyclic chain is capable to change lipophilic, complexing, biological and other properties of the initial crown-ethers. For synthesis of such compounds we have used dihalidophosphines obtained by direct substitution of the electron-rich aromatic compounds with phosphorus (III) halides. As a result, series of highly efficient macrocyclic compounds of a nowel type have been obtained.

Synthesis and characterization of topologically interesting vinyl polymers

AbstractA series of macrocyclic poly(2‐vinylpyridine)&s were synthesized by high dilution (∼10−5 M) coupling of the two‐ended living precursor dianions with 1, 2‐ and 1, 4‐bis‐(bromomethyl)benzene (1, 2‐ or 1, 4‐DBX). SEC measurements indicate that the macrocycles contain less than 5% linear precursor and that the hydrodynamic size of the macrocycles is substantially (∼30%) less than that of the linear precursor. At very low MW, the sizes of macrocyclic and linear polymers differ less, particularly for the case of the 1, 2‐DBX product. Viscometry measurements in THF of linear and macrocyclic polymers also indicated substantial size differences of linear and macrocyclic P2VP.The values of the glass transition temperature (Tg) for both the 1, 2‐ and 1, 4‐DBX macrocycles were found to increase with decreasing MW as qualitatively predicted by entropy calculations. Thus, as the degree of polymerization decreases, the macrocyclic chains become conformationally stiffer and this is reflected by higher Tg values. The differences in Tg between linear and macrocyclic P2VP are quite large (∼40K) around a DP of 40 and decrease to values of a few degrees at a DP of around 200. These differences are diagnostically useful in estimating the linear content of the macrocycles below a DP of 100.

Formation of a new macrocyclic chain polymer containing thorium(IV) and mercury(II): Structure of [Hg 2Th(C 4H 6NO) 4(NO 3) 4] n

Reaction of Hg(C 4H 6NO) 2 (where C 4H 6NO is the anion of 2-pyrrolidinone) with thorium nitrate in methanol yields a polymeric heterometallic complex, [Hg 2Th(C 4H 6NO) 4(NO 3) 4] n which has been characterized by X-ray diffraction. The crystals are monoclinic, P2 1/ c, a = 10.020(5), b = 19.421(10), c = 14.615(6) Å, β = 94.97(4)°, Z = 4. The structure was refined on 2570 reflections to R = 0.047. The compound has a polymeric chain structure with the links of the chain comprising 16-membered macrocycles, formed by two thorium, two mercury, four oxygen, four carbon and four nitrogen atoms. Each thorium atom is 10-coordinate with a distorted bicapped square antiprismatic array of oxygen atoms (four from 2-pyrrolidinone anions, four from two bidentate nitrates and two from two unidentate nitrates).

Bimetallic polymeric macrocyclic chain structures formed by lanthanide(III) nitrates and Hg(C4H6NO)2; the crystal structures of [Hg2Eu(C4H6NO)4(NO3)3] n and [Hg3Tb2(C4H6NO)6(NO3)6] n

Reaction of HgL2(L = C4H6NO, the anion of 2-pyrrolidone) with hydrated lanthanide(III)(Ln) nitrates yields two new series of polymeric heterometallic complexes of stoicheiometries Hg2LnL4(NO3)3 and Hg3Ln2L6(NO3)6, representative members of which [Ln = Eu (1) and Ln = Tb (2), respectively] have been structurally characterized.

Synthesis of macrocyclic polyether-diamides and their membrane selectivity

The preparation of a series of polyether-diamides with different structure of the macrocyclic chain is described. The ion-selective properties of these compounds with respect to ions of the I and II group were investigated electrochemically in poly(vinyl chloride) membranes plasticised with 2-nitro-1-octyloxybenzene. The relationship between the structure of ionophores and their membrane selectivity are discussed.