No abstract

While linkers with various conformations pose challenges in the design and prediction of metal–organic framework (MOF) structures, they ultimately provide great opportunities for the discovery of novel structures thereby enriching structural diversity. Tetratopic carboxylate linkers, for example, have been widely used in the formation of Zr-based MOFs due to the ability to target diverse topologies, providing a promising platform to explore their mechanisms of formation. However, it remains a challenge to control the resulting structures when considering the complex assembly of linkers with unpredicted conformations and diverse Zr6 node connectivities. Herein, we systematically explore how solvents and modulators employed during synthesis influence the resulting topologies of Zr-MOFs, choosing H4TCPB-Br2 (1,4-dibromo-2,3,5,6-tetrakis­(4-carboxyphenyl)­benzene) as a representative tetratopic carboxylate linker. By modulating the reaction conditions, the conformations of the linker and the connectivities of the Zr6 node can be simultaneously tuned, resulting in four types of structures: a new topology (NU-500), she (NU-600), scu (NU-906), and csq (NU-1008). Importantly, we have synthesized the first 5-connected Zr6 node to date with the (4,4,4,5)-connected framework, NU-500. We subsequently performed detailed structural analyses to uncover the relationship between the structures and topologies of these MOFs and demonstrated the crucial role that the flexible linker played to access varied structures by different degrees of linker deformation. Due to a variety of pore structures ranging from micropores to hierarchical micropores and mesopores, the resulting MOFs show drastically different behaviors for the adsorption of n-hexane and dynamic adsorption of 2-chloroethyl ethyl sulfide (CEES) under dry and humid conditions.

Glycerol was used, for the first time, as a green and effective promoting medium for electrophilic activation of aldehydes, and with which, a catalyst-free system for some reactions that conventionally carried out using acid catalysts, such as synthesis of di(indolyl)methanes, 3,4,5,6,7,9-hexahydro-9-aryl-1H-xanthene-1,8(2H)-dione and 1-oxo-hexahydroxanthenes, was developed.

Recent advancements in the development of conductive metal− organic frameworks (MOFs) and covalent organic frameworks (COFs) have sparked interest in a variety of applications that leverage electronic materials due to the inherent tunability, porosity, and crystallinity associated with these materials. Hydrogen-bonded organic frameworks (HOFs) comprise an emerging class of complementary porous materials that assemble crystalline networks mainly from intermolecular hydrogen-bonding interactions; however, relatively few reports on functional HOFs exist as these reversible interactions are much weaker than the coordination or covalent bonds found in the former frameworks, which presents additional challenges in the isolation and activation of HOFs. In this work, we introduce an approach to access a permanently porous HOF derived from a tetrathiafulvalene (TTF) core, which is the first HOF reported to date that exhibits electrical conductivity. Upon precipitation from solution, HOF-110 self-assembles in a preferred orientation that contains vertical columns of TTF dimers, and the postsynthetic incorporation of iodine within the nanoporous channels of this framework affords pressed pellet conductivity values of up to 6.0 × 10 −7 S•cm −1 , which is an almost 30-fold improvement compared with pressed pellets of the pristine framework. Extensive structural characterization studies suggest the presence of radical mixed-valence TTF/TTF •+ species within these materials, which is consistent with previous reports on analogous TTF-based MOFs and COFs. Overall, this work presents a viable strategy to develop robust, electrically conductive frameworks built from purely intermolecular interactions, further expanding the toolbox available for the assembly of functional porous materials.

ypically, the backbone of a wireless mesh network (WMN) is made up of dedicated wireless nodes called mesh routers (MRs), which are configured in an ad hoc mode and use omnidirectional antennas, with one or multiple wireless radio interfaces based on IEEE 802.11 technologies. These MRs can be freely organized into any network topology, and communicate with each other using protocols such as Optimized Link State Routing (OLSR) [1] and Better Approach to Mobile Ad Hoc Networking (BATMAN) [2]. However, traditional WMNs are difficult to manage and upgrade because configurations are made manually and are error-prone. It normally takes weeks or even months to provide new services for service activation, test, and assurance. Furthermore, mesh routers work in a self-organizing manner without a global view, leading to poor network resource allocation and low performance, especially in largescale networks.Software defined networking (SDN) is a promising network paradigm that significantly simplifies network management [3]. By decoupling control plane and data plane, SDN enables flexible control and dynamic resource configuration with a global view of the entire network. In this way, network policies (e.g., traffic load balancing, access control, and fault-tolerance) can be easily realized, and new services be rapidly and agilely deployed.In this article, we propose a novel architecture of softwaredefined wireless mesh networks (SD-WMNs) providing Internet services. A logically centralized controller maintains all of the network information, and conducts global resource allocation. Software-defined MRs make data forwarding according to rules specified by the controller. In particular, we extend OpenFlow [3] to implement complicated interactions between the controller and software-defined MRs in wireless networks.We then summarize several critical challenges in SD-WMNs, such as spectrum isolation of control and data planes, status monitoring and collection, and congestion control.Although the SD-WMN approach is promising due to its global network knowledge and centralized management, frequent message exchange between controller and softwaredefined MRs can lead to a high traffic load that would aggravate transmission congestion in wireless networks. In order to improve resource utilization, we examine the traffic characteristics in SD-WMNs, and propose three novel spectrum allocation and traffic scheduling algorithms, that is, Fixed-Bands Non-Sharing (FB-NS), Non-Fixed-Bands NonSharing (NFB-NS), and Non-Fixed-Bands Sharing (NFB-S) algorithms, to exploit frequency and spatial multiplexing. Finally, the performance of the proposed three algorithms are evaluated by extensive simulation. Preliminaries and the State of the Art SDN and OpenFlowSDN has been envisioned as the next generation network paradigm [3] that decouples the control plane and data plane such that complicated network logic is no longer installed in switches or routers, but at a logically centralized controller. Each switch at the data plane conducts data forward...

Micro/nanophotonic structures that are capable of optical wave-front shaping are implemented in optical waveguides and passive optical devices to alter the phase of the light propagating through them. The beam division directions and beam power distribution depend on the design of the micro/nanostructures. The ultimate potential of advanced micro/nanophotonic structures is limited by their structurally rigid, functional singleness and not tunable against external impact. Here, we propose a thermally induced optical beam-power splitter concept based on a shape memory polystyrene film with programmable micropatterns. The smooth film exhibits excellent transparency with a transmittance of 95% in the visible spectrum and optical stability during a continuous heating process up to 90 °C. By patterning double sided shape memory polystyrene film into erasable and switchable micro-groove gratings, the transmission light switches from one designed light divided directions and beam-power distribution to another because of the optical diffraction effect of the shape changing micro gratings during the whole thermal activated recovery process. The experimental and theoretical results demonstrate a proof-of-principle of the beam-power splitter. Our results can be adapted to further extend the applications of micro/nanophotonic devices and implement new features in the nanophotonics.

No abstract

The spin-polarized transport in a single-molecule magnet Fe 4 sandwiched between two gold electrodes is studied, using nonequilibrium Green's functions in combination with the density-functional theory. We predict that the device possesses spin filter effect (SFE), spin valve effect (SVE), and negative differential resistance (NDR) behavior. Moreover, we also find that the appropriate chemical ligand, coupling the single molecule to leads, is a key factor for manipulating spin-dependent transport. The device containing the methyl ligand behaves as a nearly perfect spin filter with efficiency approaching 100%, and the transport is dominated by transmission through the Fe 4 metal center. However, in the case of phenyl ligand, the spin filter effect seems to be reduced, but the spin valve effect is significantly enhanced with a large magnetoresistance ratio, reaching 1800%. This may be attributed to the blocking effect of the phenyl ligands in mediating transport. Our findings suggest that such a multifunctional molecular device, possessing SVE, NDR and high SFE simultaneously, would be an excellent candidate for spintronics of molecular devices.M olecular spintronics using molecules as spin transport elements has attracted intensive interest due to obtained various functionality, and molecular devices such as spin valve, single-molecule transistors, switch and diode, etc [1][2][3][4][5] . Conventionally, the magnetic molecule junction (MMJ) can be achieved by placing a nonmagnetic molecular bridge between two ferromagnetic electrodes 6,7 . In the rather newer field, MMJ can also be achieved by coupling a magnetic molecule to two nonmagnetic probes [8][9][10] . In this approach, singlemolecule magnets (SMMs) are ideal building blocks to construct MMJ because of their independent magnetically functional units [11][12][13] , where the inner magnetic core in SMMs is surrounded by organic ligands and the interaction between magnetic cores of neighbor molecule is very weak, leading to a large-spin ground state. Unlike above mentioned conventional MMJ depending on reasonable magnetic configuration of two ferromagnetic leads 7,14 , the origin of magnetic behavior in this MMJ consisting of a single-molecule magnet and two nonmagnetic electrodes is the intrinsic spin of the center magnetic molecule, therefore avoiding the great difficulty of the spin injection from ferromagnetic electrodes into a nonmagnetic center in real applications. And so the unique feature of MMJ containing SMM would offer much greater potential for high-density information storage devices 15 .Although there have been some successful efforts to organize SMMs on various substrates, the observation of magnetic hysteresis on individual molecules organized on surfaces 16,17 , that is a necessary step to develop molecular memory arrays, had not been reported for monolayers of SMMs when wired to metallic surfaces until Matteo Mannini and co-workers found that tailor-made tetranuclear Fe 4 complexes retain their magnetic properties at gold surfaces 15 . This...