A rotating arc gas pump for circuit breaking and other applications

A rotating arc circuit breaker is described which uses an auxiliary current source to generate the magnetic field for driving the arc. Test results obtained using optical fiber measurement systems have shown that there are three main arcing phases. Initially the arc rotates at an essentially constant but low velocity, subsequently its velocity oscillates between this and much higher values, and finally the arc plasma may become diffuse in nature. Test results obtained with dielectric strength probes have indicated that a unidirectional flow of arc heated gas is generated. The flow is away from the moving contact of the interrupter so promoting good dielectric strength in this critical contact region. The combination of the optical fiber and dielectric probe results indicates two possible modes of gas pumping represented, respectively, by a fan and a piston-type action of the arc. Simplified analytical models for both modes are developed with predictions obtained showing good agreement with the experimental results. Discussion of experimental results suggests that the transition from oscillatory velocity changes to diffuse arcing represents an important parameter for scaling the geometries of future interrupters and arc heaters

Exploring the coordination chemistry of a low symmetry, bent dipyridyl ligand

Although dipyridyl ligands are ubiquitous in their use within coordination polymers, the vast majority of these are symmetrical species (i.e. typically having a C2 axis passing through their core) based on para-substituted pyridyl groups which aids in the predictability of the networks or complexes that they form. Less symmetric species are often more difficult to utilize in the formation of predictable networks and are typically reliant on “post-synthetic rationalization” of the materials that are formed. Herein, we report an asymmetric dipyridyl ligand (L) which has a relatively rigid “kink,” and its use in the formation of several coordination polymers. Detailed structural comparison reveals the ligand to be relatively predictable with a predisposition to making M2L2 cyclic motifs due to the angle subtended between the two coordinating groups. In several instances the size of the motif formed provides a cavity in which aromatic species can reside.</p

Di- and Triammonium Salts of Carbamoyldicyanomethanide, C(CN)₂(CONH₂)⁻: Layered Organic Architectures

Layered organic structures, containing robust hydrogen-bonded anionic tapes bridged by di- and triammonium cations, have been synthesized and structurally characterized. Salts of the carbamoyldicyanomethanide (cdm) anion, C(CN)2(CONH2)−, using H3N(CH2)nNH3 cations (n = 2, 3, or 4) display layered structures containing one-dimensional (1D) hydrogen-bonded chains of cdm. The structure of (H3N(CH2)2NH3)(cdm)2 (1) forms a bilayer structure with the cation bridging, through charge-assissted hydrogen bonds, between parallel anionic ribbons containing two different synthons. The longer cation in (H3N(CH2)3NH3)(cdm)2 (2) results in a structure containing parallel anionic layers with cationic pillars running through them. The layers in 2 contain different hydrogen bonded tapes with R22(8) and R22(16) ring synthons which are also observed in the structure of (H3N(CH2)4NH3)(cdm)2 (3). Despite the differing length of the cation in 2 and 3, the distances between the layers are remarkably similar; however, the extra degree of flexibility in the (CH2)4-based cation results in the relative orientation of the layers differing. The structure of the triammonium salt (H3N(CH2)2NH2(CH2)2NH3)(cdm)3 (4) contains hydrogen-bonded anionic sheets through which the linear cations pass with each cation interacting with five different anionic layers, compared to three in the structures of 2 and 3

Interpenetration in π‑Rich Mixed-Ligand Coordination Polymers

Structural and chemical influences on interpenetration have been investigated through the preparation and structural analysis of a series of seven chiral coordination polymers using a phenyl­alanine-substituted naphthalene­diimide ligand (H₂PheNDI). The reaction of H₂PheNDI with Mn^II or Cd^II and a range of linear dipyridyl-based coligands forms a series of coordination polymers which vary greatly in terms of their topologies and interpenetration while largely retaining a common metallomacrocyclic motif. The metallomacrocyclic motif is found in a tube-like 1D coordination polymer <i>poly</i>-[Cd­(bipy)­(OH₂)­(PheNDI)] (<b>2</b>) and a closely related 2D polythreaded network <i>poly</i>-{[Cd₂­(bipy)₂­(PheNDI)₂]­[Cd­(bipy)­(DMF)_1.5­(NO₃)₂­(OH₂)_0.5]} (<b>3</b>) which are synthesized as pure phases under slightly different conditions. The longer 1,2-di­(4-pyridyl)­ethylene (dpe) ligand gives rise to a 2D coordination polymer <i>poly</i>-[Cd₄­(DMF)­(dpe)₄­(OH₂)₂­(PheNDI)₄] (<b>5</b>) in which the metallomacrocycles are connected only “sideways” rather than as a tube. This difference allows for 2-fold 2D → 2D interpenetration, between two crystallographically distinct sheets, whereby the dpe passes through the metallomacrocycle, assisted by face-to-face aromatic interactions. The use of a larger dipyridyl ligand, <i>N</i>,<i>N</i>′-bis­(4-pyridyl)­naph­thalene­diimide (4pyNDI), yielded 3D coordination polymers with distorted pcu topologies of the form <i>poly</i>-[M₂­(PheNDI)₂­(4PyNDI)₂] (M = Cd, <b>6</b>; Mn, <b>7</b>) which contain neither the metallomacrocyclic motif nor interpenetration

A Conformationally Flexible, Urea-Based Tripodal Anion Receptor: Solid-State, Solution, and Theoretical Studies

Tripodal tris(urea) cationic receptors 1 and 2 containing p-tolyl or octyl substituents, respectively, have been synthesized, and their association behavior with anionic guests has been studied via a variety of methods. The receptors are based around a hexasubstituted aryl core and contain both urea and pyridinium functionalities. For 1:1 complexes, anions reside within the central cavity of the host species, held by hydrogen bonds from both NH and CH donors. The following host−anion complexes have been characterized by X-ray crystallography:  1−(Br)3, 1−(PF6)3·2(CH3)2CO, and 1−(NO3)1.5(PF6)1.5. Each structure contains the receptor in a significantly different geometry, highlighting the anion-dependent conformational flexibility of 1. Solution 1H NMR spectroscopic titrations have shown the two host species to display significant affinity for both halides and hydrogen sulfate and strongly suggest the persistence of CH···X- interactions despite the presence of “stronger” NH donor groups. Variable-temperature 1H NMR studies on the more soluble octyl derivative 2 show that there is a distinct change in conformation associated with the formation of a 1:1 host/guest complex. Computations using density functional theory (with the B3LYP functional) have been employed to aid in understanding the geometry of the 1:1 host/chloride complexes of 1 and 2. These experiments suggest that the lowest energy conformation for 1−Cl is one in which the ureidopyridinium arms are orientated upward forming a cavity that is sealed by CH···π interactions, effectively forming a unimolecular capsule, whereas for 2 a less symmetrical “2-up, 1-down” geometry is favored

A Conformationally Flexible, Urea-Based Tripodal Anion Receptor: Solid-State, Solution, and Theoretical Studies

Tripodal tris(urea) cationic receptors 1 and 2 containing p-tolyl or octyl substituents, respectively, have been synthesized, and their association behavior with anionic guests has been studied via a variety of methods. The receptors are based around a hexasubstituted aryl core and contain both urea and pyridinium functionalities. For 1:1 complexes, anions reside within the central cavity of the host species, held by hydrogen bonds from both NH and CH donors. The following host−anion complexes have been characterized by X-ray crystallography:  1−(Br)3, 1−(PF6)3·2(CH3)2CO, and 1−(NO3)1.5(PF6)1.5. Each structure contains the receptor in a significantly different geometry, highlighting the anion-dependent conformational flexibility of 1. Solution 1H NMR spectroscopic titrations have shown the two host species to display significant affinity for both halides and hydrogen sulfate and strongly suggest the persistence of CH···X- interactions despite the presence of “stronger” NH donor groups. Variable-temperature 1H NMR studies on the more soluble octyl derivative 2 show that there is a distinct change in conformation associated with the formation of a 1:1 host/guest complex. Computations using density functional theory (with the B3LYP functional) have been employed to aid in understanding the geometry of the 1:1 host/chloride complexes of 1 and 2. These experiments suggest that the lowest energy conformation for 1−Cl is one in which the ureidopyridinium arms are orientated upward forming a cavity that is sealed by CH···π interactions, effectively forming a unimolecular capsule, whereas for 2 a less symmetrical “2-up, 1-down” geometry is favored

A Conformationally Flexible, Urea-Based Tripodal Anion Receptor: Solid-State, Solution, and Theoretical Studies

Tripodal tris(urea) cationic receptors 1 and 2 containing p-tolyl or octyl substituents, respectively, have been synthesized, and their association behavior with anionic guests has been studied via a variety of methods. The receptors are based around a hexasubstituted aryl core and contain both urea and pyridinium functionalities. For 1:1 complexes, anions reside within the central cavity of the host species, held by hydrogen bonds from both NH and CH donors. The following host−anion complexes have been characterized by X-ray crystallography:  1−(Br)3, 1−(PF6)3·2(CH3)2CO, and 1−(NO3)1.5(PF6)1.5. Each structure contains the receptor in a significantly different geometry, highlighting the anion-dependent conformational flexibility of 1. Solution 1H NMR spectroscopic titrations have shown the two host species to display significant affinity for both halides and hydrogen sulfate and strongly suggest the persistence of CH···X- interactions despite the presence of “stronger” NH donor groups. Variable-temperature 1H NMR studies on the more soluble octyl derivative 2 show that there is a distinct change in conformation associated with the formation of a 1:1 host/guest complex. Computations using density functional theory (with the B3LYP functional) have been employed to aid in understanding the geometry of the 1:1 host/chloride complexes of 1 and 2. These experiments suggest that the lowest energy conformation for 1−Cl is one in which the ureidopyridinium arms are orientated upward forming a cavity that is sealed by CH···π interactions, effectively forming a unimolecular capsule, whereas for 2 a less symmetrical “2-up, 1-down” geometry is favored

Heteroligand Molecular “Stirrups” Using Conformationally Flexible Ditopic Pyridyl−Pyrazolyl Ligands

Heteroligand molecular “stirrups” form by the self-assembly of flexible ditopic ligands in combination with 4,4′-bipyridine and [(dppp)Pd)]2+. Crystallographic analysis shows that the ligands, bis[3-(4-pyridyl)pyrazolyl]-m-xylene (mXy4py3pz) and bis[4-(4-pyridyl)pyrazolyl]-p-xylene (pXy4py4pz) form complexes of the type [{(dppp)Pd}2(4,4′-bipy)(L)]·4OTf (1·4OTf and 2·4OTf, respectively) in the solid state, with remarkably similar structures considering the differences in substitution patterns between the two ligands. The self-assembly of both 14+ and 24+ is assisted by face-to-face π interactions on the exterior of the macrocycle between the phenyl rings of the dppp ligands and the pyridyl groups of the ditopic ligands

A Conformationally Flexible, Urea-Based Tripodal Anion Receptor: Solid-State, Solution, and Theoretical Studies

Tripodal tris(urea) cationic receptors 1 and 2 containing p-tolyl or octyl substituents, respectively, have been synthesized, and their association behavior with anionic guests has been studied via a variety of methods. The receptors are based around a hexasubstituted aryl core and contain both urea and pyridinium functionalities. For 1:1 complexes, anions reside within the central cavity of the host species, held by hydrogen bonds from both NH and CH donors. The following host−anion complexes have been characterized by X-ray crystallography:  1−(Br)3, 1−(PF6)3·2(CH3)2CO, and 1−(NO3)1.5(PF6)1.5. Each structure contains the receptor in a significantly different geometry, highlighting the anion-dependent conformational flexibility of 1. Solution 1H NMR spectroscopic titrations have shown the two host species to display significant affinity for both halides and hydrogen sulfate and strongly suggest the persistence of CH···X- interactions despite the presence of “stronger” NH donor groups. Variable-temperature 1H NMR studies on the more soluble octyl derivative 2 show that there is a distinct change in conformation associated with the formation of a 1:1 host/guest complex. Computations using density functional theory (with the B3LYP functional) have been employed to aid in understanding the geometry of the 1:1 host/chloride complexes of 1 and 2. These experiments suggest that the lowest energy conformation for 1−Cl is one in which the ureidopyridinium arms are orientated upward forming a cavity that is sealed by CH···π interactions, effectively forming a unimolecular capsule, whereas for 2 a less symmetrical “2-up, 1-down” geometry is favored

Heteroligand Molecular “Stirrups” Using Conformationally Flexible Ditopic Pyridyl−Pyrazolyl Ligands

Heteroligand molecular “stirrups” form by the self-assembly of flexible ditopic ligands in combination with 4,4′-bipyridine and [(dppp)Pd)]2+. Crystallographic analysis shows that the ligands, bis[3-(4-pyridyl)pyrazolyl]-m-xylene (mXy4py3pz) and bis[4-(4-pyridyl)pyrazolyl]-p-xylene (pXy4py4pz) form complexes of the type [{(dppp)Pd}2(4,4′-bipy)(L)]·4OTf (1·4OTf and 2·4OTf, respectively) in the solid state, with remarkably similar structures considering the differences in substitution patterns between the two ligands. The self-assembly of both 14+ and 24+ is assisted by face-to-face π interactions on the exterior of the macrocycle between the phenyl rings of the dppp ligands and the pyridyl groups of the ditopic ligands