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•Metal organic nanotube.•Synthetic strategies.•Formation mechanism.•Crystal structures.•Properties.
This tutorial review provides basic design principles and the current status of ...metal-organic nanotubes (MONTs). As an attractive family of nanotubular materials, MONTs can show precise structures that can be designed and constructed through judicious choice of metal ions and ligands, and also interesting physical and chemical properties that can be embedded within the structures. This review summarizes the recent progress in this topical field including the synthetic approaches towards the nanotubular structures, the formation mechanism, the crystal structures of MONTs reported thus far with finite and infinite sizes, and also the physical and chemical properties. The review concludes with a discussion of future challenges for development of this promising field.
Artificial smart materials with switchable multifunctionality are of immense interest owing to their wide application in sensors, displays and memory devices. Lanthanide complexes are promising ...multifunctional materials integrating optical and magnetic characteristics. However, synergistic manipulation of different physical properties in lanthanide systems is still challenging. Herein we designed and synthesized a mononuclear complex Dy
III
(SCN)
3
(depma)
2
(4-hpy)
2
(
1
), which incorporates 9-diethylphosphonomethylanthracene (depma) as a photo-active component and 4-hydroxypyridine (4-hpy) as a polar component. This compound shows several unusual features: (a) reversible thermo-responsive phase transition associated with the order-disorder transition of 4-hpy and SCN
−
, which leads to thermochromic behavior and dielectric anomaly; (b) reversible photo-induced dimerization of anthracene groups, which leads to synergistic switching of luminescence, magnetic and dielectric properties. To our knowledge, compound
1
is the first example of lanthanide complexes that show stimuli-triggered synergistic and reversible switching of luminescence, magnetic and dielectric properties.
Dy
III
(SCN)
3
(depma)
2
(4-hpy)
2
(
1
) shows reversible thermo-induced phase transition associated with thermochromism and dielectric anomaly and photo-induced dimerization with synergistic switching of luminescence, magnetic and dielectric properties.
Chiral lanthanide clusters have promising applications in chiral recognition, magneto‐optical memories, and spintronic devices. Nonetheless, the precise prediction and controlled development of ...homochiral polynuclear Ln‐complexes is still a challenge. Herein, through multidentate chelate synthetic strategy, a new homochiral hexagadolinium phosphonate cluster designated as R/S‐Gd6(pmhpH)8(NO3)2(H2O)8⋅19H2O (R/S‐1) was successfully obtained by reacting chiral phosphonomethylhomoproline(pmhpH3) with Gd(III) salt. The cluster, shaped like a lantern, is constructed from {GdO8} polyhedra and {PO3C} tetrahedra surrounded by eight pmhpH2− ligands. Within the structure, two types of gadolinium ions with different coordination modes are observed. Each Gd(III) ion is bound to two carboxylate oxygens and six phosphonate oxygens from the coordinated pmhpH2− ligands. Circular dichroism spectra comfirmed that R/S‐1 exists as a pair of enantiomers. Moreover, the cluster exhibits high thermal stability, decomposing at temperatures exceeding 335 °C. Notably, the chiral cluster materials can be used for enantiomeric recognition for tryptophan (Trp) with the differential pulse voltammetry (DPV) peak current ratio (ID/IL) 2.74. Besides, the magnetic measurements revealed that compound R‐1 exhibits a good magnetocaloric effect (MCE) with a maximum entropy change of −ΔSmmax=36.84 Jkg−1 K−1 at T=2 K and ΔH=7 T.
Homochiral hexagadolinium phosphonate clusters R/S‐Gd6(pmhpH)8(NO3)2(H2O)8⋅19H2O (R/S‐1) were synthesized through multidentate chelate synthetic strategy. Notably, the chiral cluster materials can be used for enantiomeric recognition for tryptophan (Trp) with the DPV peak current ratio (ID/IL) 2.74. The magnetic measurements show the compound R‐1 displays good magnetocaloric effect (MCE) with −ΔSmmax=36.84 Jkg−1 K−1 at T=2 K and ΔH=7 T.
Nanotubular materials have garnered considerable attention since the discovery of carbon nanotubes. Although the layer-to-tube rolling up mechanism has been well recognized in explaining the ...formation of many inorganic nanotubes, it has not been generally applied to coordination polymers (CPs). To uncover the key factors that determine the rolling-up of layered CPs, we have chosen the Co/R-, S-Xpemp Xpemp = (4-X-1-phenylethylamino)methylphosphonic acid, X = H, F, Cl, Br systems and study how the weak interactions influence the formation of layered or tubular structures. Four pairs of homochiral isostructural compounds R-, S-Co(Xpemp)(H2O)2 X = H (1H), F (2F), Cl (3Cl), Br (4Br) were obtained with tubular structures. The inclusion of 3,3′-azobipyridine (ABP) guest molecules led to compounds R-, S-Co(Xpemp)(H2O)24·ABP·H2O with layered structures when X was Cl (5Cl) and Br (6Br), but tubular compounds 1H and 2F when X was H and F. Layered structures were also obtained for racemic compounds meso-Co(Xpemp)(H2O)2 X = F (7F), Cl (8Cl), Br (9Br) using racemic XpempH2 as the reaction precursor, but not when X = H. A detailed study on R- 6Br revealed that layer-to-tube transformation occurred upon removal of ABP under hydrothermal conditions, forming R- 4Br with a tubular structure. Similar layer-to-tube conversion did not occur in organic solvents. The results demonstrate that weak interlayer interactions are a prerequisite but not sufficient for the rolling-up of the layers. In the present cases, water also provides a driving force in the layer-to-tube transformation. The experimental results were rationalized by theoretical calculations.
Systematic control of the intermolecular pair-wise 4 + 4 photocycloaddition of a series of dysprosium phosphonates through fine-tuning of two different phosphonate ligands, one with a bidentate ...blocker and one with an anthracene antenna, both with alkyl substituents, reveals a size dependent rate. With bulky isopropyl on the diphosphonate blocker little response to UV light is observed. In contrast, compounds with ethyl which has less steric hindrance exhibit almost complete photocycloaddition. Interestingly, the alkyl substituents attached to anthracene monophosphonate have no evident effect on the reaction rate. Although no direct relationship can be found between the substitutions and the observed differences in field-induced single molecule magnetism, remarkable changes in magnetic dynamics are observed for complexes before and after the complete photocycloaddition reactions.
Systematic control of 4 + 4 photocycloaddition of dysprosium phosphonates through fine-tuning of two different phosphonate ligands with alkyl substituents reveals a size dependent rate with remarkable changes in the luminescence and magnetic dynamics.
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, C6H5, 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.
The morphologies of 1D coordination polymers of GdIII(R‐pempHx)3(anion)(3‐3x) can be controlled by the combined effect of pH and anions. Superhelices were formed when anions with larger sizes and enhanced anion‐chain interactions, such as I− (and I3−), C6H5SO3− and CF3SO3−, were present in the systems. When the anion is CF3SO3−, a complete chirality inversion from left‐ to right‐handedness was observed by raising the pH of the reaction mixture.
ABSTRACT
Observationally, the mysterious fast radio bursts (FRBs) are classified as repeating ones and apparently non-repeating ones. While repeating FRBs cannot be classified into the non-repeating ...group, it is unknown whether the apparently non-repeating FRBs are actually repeating FRBs whose repetitions are yet to be discovered, or whether they belong to another physically distinct type from the repeating ones. In a series of two papers, we attempt to disentangle this mystery with machine learning methods. In this first paper, we focus on an array of supervised machine learning methods. We train the machine learning algorithms with a fraction of the observed FRBs in the first CHIME/FRB catalogue, telling them which ones are apparently non-repeating and which ones are repeating. We then let the trained models predict the repetitiveness of the rest of the FRB data with the observed parameters, and we compare the predictions with the observed repetitiveness. We find that the models can predict most FRBs correctly, hinting towards distinct mechanisms behind repeating and non-repeating FRBs. We also find that the two most important distinguishing factors between non-repeating and repeating FRBs are brightness temperature and rest-frame frequency bandwidth. By applying the trained models back to the entire first CHIME catalogue, we further identify some potentially repeating FRBs currently reported as non-repeating. We recommend a list of these bursts as targets for future observing campaigns to search for repeated bursts in a combination with the results presented in Paper II using unsupervised machine learning methods.
Homochiral iron(ii)-based nanotubular metal phosphonates (R)- and (S)-Fe(pemp)(H2O)2 pemp2- = (R)- or (S)-(1-phenylethylamino)methylphosphonate are reported showing metamagnetism at low temperature. ...The dehydrated product features coordinatively unsaturated and redox-active metal ion sites that enable it to strongly bind nitric oxide at room temperature.
ABSTRACT
Fast radio bursts (FRBs) are one of the most mysterious astronomical transients. Observationally, they can be classified into repeaters and apparent non-repeaters. However, due to the lack ...of continuous observations, some apparent repeaters may have been incorrectly recognized as non-repeaters. In a series of two papers, we intend to solve such problem with machine learning. In this second paper of the series, we focus on an array of unsupervised machine learning methods. We apply multiple unsupervised machine learning algorithms to the first Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst catalogue to learn their features and classify FRBs into different clusters without any premise about the FRBs being repeaters or non-repeaters. These clusters reveal the differences between repeaters and non-repeaters. Then, by comparing with the identities of the FRBs in the observed classes, we evaluate the performance of various algorithms and analyse the physical meaning behind the results. Finally, we recommend a list of most credible repeater candidates as targets for future observing campaigns to search for repeated bursts in combination of the results presented in Paper I using supervised machine learning methods.
Inspired by natural biological systems, chiral or handedness inversion by altering external and internal conditions to influence intermolecular interactions is an attractive topic for regulating ...chiral self-assembled materials. For coordination polymers, the regulation of their helical handedness remains little reported compared to polymers and supramolecules. In this work, we choose the chiral ligands
R
-pempH
2
(pempH
2
= (1-phenylethylamino)methylphosphonic acid) and
R
-XpempH
2
(X = F, Cl, Br) as the second ligand, which can introduce C-H π and C-H X interactions, doped into the reaction system of the Tb(
R
-cyampH)
3
·3H
2
O (cyampH
2
= (1-cyclohexylethylamino)methylphosphonic acid) coordination polymer, which itself can form a right-handed superhelix by van der Waals forces, and a series of superhelices
R
-1H-
x
,
R
-2F-
x
,
R
-3Cl-
x
, and
R
-4Br-
x
with different doping ratios
x
were obtained, whose handedness is related to the second ligand and its doping ratio, indicating the decisive role of interchain interactions of different strengths in the helical handedness. This study could provide a new pathway for the design and self-assembly of chiral materials with controllable handedness and help the further understanding of the mechanism of self-assembly of coordination polymers forming macroscopic helical systems.
Macroscopic chirality of right-handed Tb(
R
-cyampH)
3
·3H
2
O superhelices can be inversed by controlling the doping ratio of homochiral ligand analogue
R
-XpempH
2
(X = H, F, Cl, Br), where pempH
2
can introduce new weak interactions into the system.
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