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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.
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.
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.
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.
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.
Chiral transcription from the molecular level to the macroscopic level by self-organization has been a topic of considerable interest for mimicking biological systems. Homochiral coordination ...polymers (CPs) are intriguing systems that can be applied in the construction of artificial helical architectures, but they have scarcely been explored to date. Herein, we propose a new strategy for the generation of superhelices of 1D CPs by introducing flexible cyclohexyl groups on the side chains to simultaneously induce interchain van der Waals interactions and chain misalignment due to conformer interconversion. Superhelices of
S
- or
R
-Tb(cyampH)
3
·3H
2
O (
S
-1H
,
R
-1H
) cyampH
2
=
S
- or
R
-(1-cyclohexylethyl)aminomethylphosphonic acid were obtained successfully, the formation of which was found to follow a new type of "chain-twist-growth" mechanism that had not been described previously. The design strategy used in this work may open a new and general route to the hierarchical assembly and synthesis of helical CP materials.
Superhelices of terbium phosphonates formed following a new type of "chain-twist-growth" mechanism involving flexible cyclohexyl groups.
Despite the increasing importance and critical needs, reconfigurable radio frequency (RF) multiband filters are currently underdeveloped even both RF electronics and photonics technologies are being ...explored. Although RF multiband filters with large numbers of simultaneous passbands and wide frequency tuning range are extremely desired, achieving such functionality is extremely challenging. In this paper, a photonics-based highly tunable and reconfigurable RF multiband filter is proposed through the combination of a special designed tunable Mach-Zehnder interferometer and a reconfigurable Lyot loop filter. Both the passband frequencies and the number of simultaneous passbands are adjustable, that one or multiple passbands are continuously tuned over a 20 GHz frequency range, and the number of simultaneous passbands is reconfigurable from zero to seven. As a result, the proposed RF multiband filter can be configured with various passband combinations through the same setup, providing exceptional operation flexibility. Furthermore, broadband operation and excellent filter selectivity are obtained, with sharp passband profiles and over 35-dB sidelobe suppression.
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