Discrete Complex Research Articles

Self-Assembly, Structural Transformation, and Guest-Binding Properties of Supramolecular Assemblies with Triangular Metal–Metal Bonded Units

The properties of supramolecular structures are highly dependent on their metal-centered building blocks and organic linkers, thus the search for novel systems will lead to new functions and applications for these unique assemblies. Here, two discrete triangular trimetallic sandwich building blocks were developed to construct supramolecular assemblies through coordination-driven self-assembly with organosulfur ligands. A series of tubelike (Tr2Pd3)4L6 assemblies (Tr = cycloheptatrienyl ring) were obtained from a discrete triangular tripalladium sandwich complex with bifunctional organosulfur ligands. By replacing the metal centers of the platinum analogue, the self-assembly process resulted in the clean formation of (Tr2Pt3)2L3 triple helicates instead of tubelike species. The trimetallic sandwich building blocks were also shown to form face-capped (Tr2M3)4L4 (M = Pd or Pt) tetrahedral cages when trifunctional organosulfur ligands were used. The supramolecular assemblies were comprehensively analyzed by X-ray crystallography. A metal-cluster-induced structural transformation between (Tr2Pd3)4L4 tubes and (Tr2Pt3)2L3 triple helicates was observed. Furthermore, the face-capped (Tr2Pd3)4L4 cage possesses a tetrahedral cavity allowing the encapsulation of a series of guests.

Spin-frustration with two quasi-degenerated spin states of a copper(II) heptanuclear complex obtained from an amino acid ligand.

The Cu(ii) heptanuclear complex (Cu7atac) was synthesised using the hydrated amino acid ligand 2-(5-amino-1H-1,2,4-triazol-3-yl)acetic acid (Hatac·H2O). Single crystal X-ray diffraction analysis revealed a μ3-hydroxo bridged Cu(ii) heptanuclear complex, consisting of two triangular subunits and one Cu(ii) ion as a bridge with the formula [Cu7(atac)6(μ3-OH)2(NO3)2(H2O)10](NO3)4. The magnetic behaviour of this discrete 0D complex shows strong antiferromagnetic couplings between Cu(ii) mediated by N,N bonding and an anti-anti modes of the carboxylate anion of the ligand atac-. The magnetic data were fitted considering a 3J model. To support the model used to fit the magnetic data of the Cu7atac complex, theoretical calculation methods (complete active space self-consistent field, CASSCF, density functional theory (DFT) using the UKS TPSS/Def2-TZVP//Def2-SVP level and periodic boundary conditions (PBC) using PBE/DZVP-MOLOPT-GTH) were performed to obtain the spin states, spin density map and J couplings. The theoretical results suggest that Cu7atac is a spin-frustrated complex in the ground state, in which the doublet spin state co-exists with the quartet spin state.

Set-membership filtering for a class of nonlinear complex networks with mixed time-delays and incomplete measurements

In this paper, the set-membership filtering problem is discussed for a class of discrete time-varying nonlinear complex networks with mixed time-delays and incomplete measurements. Both the process noise and the measurement noise are unknown but bounded. The nonlinear function is assumed to satisfy the sector bounded condition and the incomplete measurement is model by a diagonal matrix. The main purpose of this paper is to design a set-membership filtering method in order to provide the certain regions, which include the real states. Accordingly, the filtering errors at each time can be limited to the ellipsoid sets for the considered nonlinear delayed complex networks in the simultaneous presence of unknown but bounded noise, mixed time-delays and incomplete measurements. Moreover, a convex optimization method is presented to obtain the minimum ellipsoid domain. In addition, the filter gain matrix can be obtained by solving a series of linear matrix inequalities. Finally, a simulation example is used to illustrate the effectiveness of the proposed set-membership filtering method.

On the importance of π-hole spodium bonding in tricoordinated HgII complexes.

A new coordination polymer [Hg(LI)I]n (1) and a new discrete coordination complex [Hg(HLII)I2] (2) are synthesized and X-ray characterized. The existence of positive π-holes at the spodium atoms in both compounds is evidenced by DFT calculations. In 1, a Hg-S semicoordination bond and a HgI spodium bond are formed at opposite sides of the π-hole. In 2, two different HgI spodium bonds are formed at both sides of the π-hole. This is the first study describing structure-guiding π-hole spodium bonding.

Tuning of Discrete Complex Proportional Integral Current Controller for Grid-Connected Converters Based on Critical Damping

Current control is of utmost importance for grid-connected converters to achieve a high level of performance. The complex proportional integral controller is usually employed for its excellent performance in terms of cross-coupling decoupling and stability. The pole/zero cancellation characteristic of the complex proportional integral controller, which is always valid in the continues-time domain, fails in the discrete-time domain, resulting in an oscillatory or even unstable response. The discrete complex proportional integral controller has thus been addressed in this work, which cancels the complex plant pole with a matching zero provided by the controller in the discrete-time domain. It has been proved that pole/zero cancellation of the discrete complex proportional integral controller is always valid, regardless of the variation of the excitation frequency. An important feature of performance independence from the pulse ratio is thus achieved. Also, to achieve the possible highest performance, a tuning method based on critical damping is developed in the discrete-time domain, which addresses the one-sample delay directly in the tuning process. In this manner, the minimum settling time and negligible overshoot for transient response can be achieved, along with the most enhanced stability and avoidance of closed-loop anomalous peaks. Experimental results have verified the effectiveness of the developed method.

In-MOF-derived ultrathin heteroatom-doped carbon nanosheets for improving oxygen reduction.

For electrocatalysis, the development of highly active and low-cost stable electrocatalysts, which would be directly applied in cathodes for fuel cells that are regarded as the most promising candidates for clean energy conversion in the quest for alternatives to conventional fossil fuel technology, remains a massive challenge. In this context, oxygen reduction reaction (ORR) is a critical process under intense research for the direct conversion of chemical energy into electricity. Herein, a facile synthetic method is proposed for the preparation of hierarchically porous 2-dimensional nanosheets consisting of Fe4C and FeCo nanoparticles incorporated in N/S-doped carbon materials at 900 °C, denoted as InFeCo@CNS900. This composite can be conveniently prepared by directly calcining the crystalline indium-organic framework of InOF-24, which is impregnated with the ferric thiocyanate and cobalt ammonium complexes under Ar atmosphere, in which Fe4C and FeCo nanoparticles were in situ formed and embedded into the well-developed carbon materials, which display the hierarchically porous nanosheets with microporous and mesoporous structures. Due to the synergistic effects between different active substances, high specific surface area, suitable graphitization degree, and rich active sites, the as-obtained InFeCo@CNS900 electrocatalyst exhibits an excellent ORR activity, which shows a lower Tafel slope of 59.5 mV dec-1, higher diffusion limit current of 5.15 mA cm-2, and better stability than the commercial 20 wt% Pt/C catalyst. This study provides a facile approach for the design and synthesis of highly efficient non-noble metal-doped carbon materials with a unique 2-dimensional morphology, which are potentially applied in energy science and technology.

Architectural and catalytic aspects of designer materials built using metalloligands of pyridine-2,6-dicarboxamide based ligands.

This perspective presents the design, synthesis and crystal structures of a large number of architectures constructed using assorted metalloligands of pyridine-2,6-dicarboxamide based ligands. The metalloligands offered various appended functional groups, whereas design strategies included varying both their position and number. A combination of these parameters resulted in the development of assorted architectures including discrete trinuclear and tetranuclear complexes as well as 1D/2D/3D coordination polymers. The metalloligand strategy not only assisted in the construction of ordered crystalline materials with varied dimensionalities but also judiciously allowed the incorporation of Lewis acidic and redox-active secondary metals in the resultant architectures. As a result, such designer architectures illustrated their noteworthy role both as homogenous and heterogeneous catalysts in different organic transformation reactions.

A Journey From Improper Gaussian Signaling to Asymmetric Signaling

The deviation of continuous and discrete complex random variables from the traditional proper and symmetric assumption to a generalized improper and asymmetric characterization (accounting correlation between a random entity and its complex conjugate), respectively, introduces new design freedom and various potential merits. As such, the theory of impropriety has vast applications in medicine, geology, acoustics, optics, image and pattern recognition, computer vision, and other numerous research fields with our main focus on the communication systems. The journey begins from the design of improper Gaussian signaling in the interference-limited communications and leads to a more elaborate and practically feasible asymmetric discrete modulation design. Such asymmetric shaping bridges the gap between theoretically and practically achievable limits with sophisticated transceiver and detection schemes in both coded/uncoded wireless/optical communication systems. Interestingly, introducing asymmetry and adjusting the transmission parameters according to some design criterion render optimal performance without affecting the bandwidth or power requirements of the systems. This dual-flavored article initially presents the tutorial base content covering the interplay of reality/complexity, propriety/impropriety and circularity/noncircularity and then surveys majority of the contributions in this enormous journey.

Synthesis, structural diversity, luminescent properties and antibacterial effects of cadmium(II) and silver(I) coordination compounds with bis(1,2,3-benzotriazol-1-yl)alkanes

A series of bis(benzo-1,2,3-triazolyl)alkanes were prepared by the reaction of 1,2,3-benzotriazole with the corresponding dibromoalkanes. Individual isomers of these flexible polydentate ligands were separated by selective copper(II) chloride complex formation. Seven new coordination compounds of 1,3-bis(benzo-1,2,3-triazol-1-yl)propane (L3), 1,4-bis(benzo-1,2,3-triazol-1-yl)butane (L4) and 1,6-bis(benzo-1,2,3-triazol-1-yl)hexane (L6) with cadmium(II) or silver(I) nitrates were prepared, characterized by single crystal X-ray diffraction, IR spectroscopy, thermogravimetric analysis and luminescence studies. It was found that depending on the solvent used, cadmium(II) nitrate forms discrete binuclear complex with the ligand L3 in acetone and 1D coordination polymer in acetonitrile. Ligands L4 and L6 with longer linkers formed 2D coordination polymers with silver nitrate both in acetone and acetonitrile. Silver coordination polymer with L6 demonstrated bactericidal effect towards Staphylococcus albus, Pseudomonas aeruginosa and Klebsiella pneumonia bacteria.

Catalytic activity of Pd dithiolate complexes with large‐bite‐angle diphosphines in Heck coupling reactions

Palladium(II) complexes of aryl dithiolates and wide‐bite‐angle diphosphines Xantphos and dppf have been developed as efficient catalysts in Suzuki and Suzuki carbonylation reactions. The catalytic activity of these highly stable, discrete and charged complexes was investigated in Heck coupling reactions of styrene and a variety of aryl bromides. Under optimized reaction conditions these palladium complexes showed excellent activity with high turnover number (6 × 106) and high turnover frequency (4 × 105 h−1). The effect of bite angle of diphosphines on the catalytic activity of the complexes [Pd2(P∩P)2(SC12H8S)]2(OTf)4 followed the trend P∩P = Xantphos > dppf > dppe as the order of their bite angles. The catalyst could be reused, and after three cycles the formation of significant amount of Pd nanoparticles was noticed, which were characterized using powder X‐ray diffraction, energy‐dispersive X‐ray analysis and transmission electron microscopy. The high catalytic activity has been attributed to the Pd nanoparticles.

A Twisted Tetragold Cyclophane from a Fused Bis-Imidazolindiylidene

The reaction between an angular bis-imidazolidinium salt and [AuCl(SMe)2] allowed the preparation of a discrete digold complex, with a rigid angular bridging bis-imidazolindiylidene ligand. This co...

AtFKBP53: a chimeric histone chaperone with functional nucleoplasmin and PPIase domains.

FKBP53 is one of the seven multi-domain FK506-binding proteins present in Arabidopsis thaliana, and it is known to get targeted to the nucleus. It has a conserved PPIase domain at the C-terminus and a highly charged N-terminal stretch, which has been reported to bind to histone H3 and perform the function of a histone chaperone. To better understand the molecular details of this PPIase with histone chaperoning activity, we have solved the crystal structures of its terminal domains and functionally characterized them. The C-terminal domain showed strong PPIase activity, no role in histone chaperoning and revealed a monomeric five-beta palm-like fold that wrapped over a helix, typical of an FK506-binding domain. The N-terminal domain had a pentameric nucleoplasmin-fold; making this the first report of a plant nucleoplasmin structure. Further characterization revealed the N-terminal nucleoplasmin domain to interact with H2A/H2B and H3/H4 histone oligomers, individually, as well as simultaneously, suggesting two different binding sites for H2A/H2B and H3/H4. The pentameric domain assists nucleosome assembly and forms a discrete complex with pre-formed nucleosomes; wherein two pentamers bind to a nucleosome.

Evolution of triple junctions’ network during severe plastic deformation of copper alloys – a discrete stochastic modelling

ABSTRACTProposed is a methodology for an accurate description of triple junctions’ network evolution in the course of severe plastic deformation (SPD). It is based on representations of polycrystalline solids with discrete combinatorial complexes, processes evolving different substructures (grains, grain boundaries, triple junctions) of these complexes, and methods for analyses of such substructures. It is demonstrated that the methodology can reproduce theoretical results available for the simplest case of quasi-homogeneous microstructure evolution, i.e. spatially random conversion of low to high angle grain boundaries during SPD. It is further shown that the proposed discrete approach can reproduce in a natural way results from recent experiments with copper alloys, where inhomogeneity development during SPD is strongly manifested. Finally, the evolution of different types of triple junctions and their connectivity is analysed to show that these substructure characteristics differentiate inhomogeneous from homogeneous evolution of the polycrystalline solid. It is suggested that such substructure characteristics can form the basis for characterisation of continuous dynamic recrystallisation process.

Resilient Set-membership State Estimation for Uncertain Complex Networks with Sensor Saturation under Round-Robin Protocol

This article gives primarily attention to the resilient set-membership state estimation problem for a class of discrete time-varying complex networks with distributed delays, uncertain inner coupling and sensor saturation under the round-robin (RR) protocol. The process and measurement noises are unknown but bounded, which are confined to the ellipsoidal sets. The RR protocol is utilized to assign the priority of accessing to the communication network to nodes in terms of a fixed circular order. By means of the recursive linear matrix inequality (RLMI) technique, a sufficient criterion is established to guarantee that the one-step ahead estimation error is confined to the ellipsoidal set. In term of the convex optimization approach and the recursive algorithm, the desired estimator gains can be derived by utilizing the sufficient condition and optimizing the corresponding constraint matrices. Finally, a simulation example is used to verify the effectiveness of the designed resilient set-membership state estimation scheme.

Crystal structure of pyridinium tetra-iso-thio-cyanato-dipyridine-chromium(III) pyridine monosolvate.

In the crystal structure of the title compound, (C5H6N)[Cr(NCS)4(C5H5N)2]·C5H5N, the CrIII ions are octa-hedrally coordinated by four N-bonding thio-cyanate anions and two pyridine ligands into discrete negatively charged complexes, with the CrIII ion, as well as the two pyridine ligands, located on crystallographic mirror planes. The mean planes of the two pyridine ligands are rotated with respect to each other by 90°. Charge balance is achieved by one protonated pyridine mol-ecule that is hydrogen bonded to one additional pyridine solvent mol-ecule, with both located on crystallographic mirror planes and again rotated by exactly 90°. The pyridinium H atom was refined as disordered between both pyridine N atoms in a 70:30 ratio, leading to a linear N-H⋯N hydrogen bond. In the crystal, discrete complexes are linked by weak C-H⋯S hydrogen bonds into chains that are connected by additional C-H⋯S hydrogen bonding via the pyridinium cations and solvent mol-ecules into layers and finally into a three-dimensional network.

Crystal structure, synthesis and thermal properties of bis-(aceto-nitrile-κN)bis-(4-benzoyl-pyridine-κN)bis-(iso-thio-cyanato-κN)nickel(II).

In the crystal structure of the title com-pound, [Ni(NCS)2(CH3CN)2(C12H9NO)2] or Ni(NCS)2(4-benzoyl-pyridine)2(aceto-nitrile)2, the NiII ions are octa-hedrally coordinated by the N atoms of two thio-cyanate anions, two 4-benzoyl-pyridine ligands and two aceto-nitrile mol-ecules into discrete com-plexes that are located on centres of inversion. In the crystal, the discrete com-plexes are linked by centrosymmetric pairs of weak C-H⋯S hydrogen bonds into chains. Thermogravimetric measurements prove that, upon heating, the title com-plex loses the two aceto-nitrile ligands and transforms into a new crystalline modification of the chain com-pound [Ni(NCS)2(4-benzoyl-pyridine)2], which is different from that of the corresponding CoII, NiII and CdII coordination polymers reported in the literature. IR spectroscopic investigations indicate the presence of bridging thio-cyanate anions but the powder pattern cannot be indexed and, therefore, this structure is unknown.

Slow Magnetic Relaxation, Antiferromagnetic Ordering, and Metamagnetism in MnII (H2 dapsc)-FeIII (CN)6 Chain Complex with Highly Anisotropic Fe-CN-Mn Spin Coupling.

Reactions of [Mn(H2 dapsc)Cl2 ]⋅H2 O (dapsc=2,6- diacetylpyridine bis(semicarbazone)) with K3 [Fe(CN)6 ] and (PPh4 )3 [Fe(CN)6 ] lead to the formation of the chain polymeric complex {[Mn(H2 dapsc)][Fe(CN)6 ][K(H2 O)3.5 ]}n ⋅1.5n H2 O (1) and the discrete pentanuclear complex {[Mn(H2 dapsc)]3 [Fe(CN)6 ]2 (H2 O)2 }⋅4 CH3 OH⋅3.4 H2 O (2), respectively. In the crystal structure of 1 the high-spin [MnII (H2 dapsc)]2+ cations and low-spin hexacyanoferrate(III) anions are assembled into alternating heterometallic cyano-bridged chains. The K+ ions are located between the chains and are coordinated by oxygen atoms of the H2 dapsc ligand and water molecules. The magnetic structure of 1 is built from ferrimagnetic chains, which are antiferromagnetically coupled. The complex exhibits metamagnetism and frequency-dependent ac magnetic susceptibility, indicating single-chain magnetic behavior with a Mydosh-parameter φ=0.12 and an effective energy barrier (Ueff /kB ) of 36.0 K with τ0 =2.34×10-11 s for the spin relaxation. Detailed theoretical analysis showed highly anisotropic intra-chain spin coupling between [FeIII (CN)6 ]3- and [MnII (H2 dapsc)]2+ units resulting from orbital degeneracy and unquenched orbital momentum of [FeIII (CN)6 ]3- complexes. The origin of the metamagnetic transition is discussed in terms of strong magnetic anisotropy and weak AF interchain spin coupling.

Synthesis, reactivity, X-ray characterization and docking studies of N7/N9-(2-pyrimidyl)-adenine derivatives

The reaction of adenine with 2-chloropyrimidine yields as a major product the unexpected N7-(2-pyrimidyl)-adenine (1) and as a minor one N9-(2-pyrimidyl)-adenine (2). Both compounds have been characterized by X-ray diffraction analysis. Moreover, we report the formation of a 1:1 co-crystal (3) composed by compound (1) and adenine that was formed serendipitously during the synthesis of (1). Unexpectedly, the treatment of (1) with Brönsted acids like HCl or HNO3 causes the opening of the imidazole ring of the N7-substituted adenine, yielding N5-(pyrimidin-2-yl)pyrimidine-4,5,6-triamine (4–7) which we have X-ray characterized in its neutral, (4), monoprotonated [nitrate salt (6)] and diprotonated forms [hydrochloride salt (5) and, also, a tetrachlorozincate salt (7)]. Finally, we have used compound (5) as ligand to synthesize and X-ray characterize its complexes with Ir(III) and Ag(I) (compounds (8) and (9), respectively), where the latter is a 2D coordination polymer and the former is a discrete mononuclear complex. We have studied the supramolecular assemblies formed in the solid state by using density functional theory (DFT) calculations. Finally, DNA-docking studies of several compounds have been carried out in order to analyze their ability to interact with the DNA.

Self-assembled coordination thioether silver(I) macrocyclic complexes for homogeneous catalysis

The bis-ortho-thioether 9,10-bis[(o-methylthio)phenyl]anthracene was synthesized as a syn-atropisomer, as revealed by X-ray diffraction. This alkylaryl thioether ligand (L) formed different macrocyclic complexes by coordination with silver(I) salts depending on the nature of the anion: M2L2 for AgOTf and AgOTFA, M6L4 for AgNO3. A discrete M2L complex was obtained in the presence of bulky PPh3AgOTf. These silver(I) complexes adopted similar structures in solution and in the solid state. As each sulfur atom in the ligand is prochiral, macrocycles L2M2 were obtained as mixtures of diastereoisomers, depending on the configurations of the sulfur atoms coordinated to silver cations. The X-ray structures of the two L2·(AgOTf)2 stereoisomers highlighted their different geometry. The catalytic activity of all silver(I) complexes was effective under homogeneous conditions in two tandem addition/cycloisomerization of alkynes using 0.5–1 mol % of catalytic loading.

Oblique-slip tectonics in an active volcanic chain: A case study from the Southern Andes

Oblique-slip tectonics in the intra-arc region of the Southern Andes accommodates heterogeneous deformation derived from plate convergence during the Pliocene and Quaternary. Long-term mechanical interaction between Andean transverse faults (i.e. NW-striking sinistral faults) and margin-parallel faults (i.e. NNE-striking faults) results in linked transtensional fault damage zones that facilitate structural conditions for the migration and emplacement of geofluids in the upper crust. We investigated the architecture of pre-eruptive units and the nature of faulting at the Tatara–San-Pedro–Pellado volcanic complex in the Southern Andes. Here, oblique-slip faulting crosscuts Miocene folded strata and granitoids. Our main results suggest that Quaternary volcanism and an associated geothermal systems developed on top of an ENE-oriented structural anisotropy defined by hundreds of faults and dikes interacting in a ca. 9km long and 4km wide rock volume, named the Tatara Damage Zone. Deformation in this domain is characterized by ENE- to WNW-striking transtensional oblique-slip faults flanked by (1) the seismically active NS-striking (dextral) Melado Fault to the west, (2) discrete NS- to ENE-striking dextral splay faults to the east and (3) the sinistral NW-striking Los Cóndores Fault to the north-east, which is reported for the first time in this work. The latter fault represents an excellent example of a long-lived Andean Transverse Fault. Furthermore, we suggest that the Los Cóndores Fault accommodates a margin-oblique slip component of bulk transpressional deformation. We demonstrate that Pliocene–Quaternary intra-arc oblique faulting developed after pre-Late Miocene compressional tectonics, and that this oblique faulting constrains the geometry of permeable pathways for the flow, emplacement, and eruption of quaternary geofluids. Furthermore, we evaluated the stress field for a discrete volcanic complex and provided key elements to better understand the role of Andean Transverse Faults in the spatial organization of Quaternary arc volcanism and geothermal systems in the Southern Andes.