The ligand, the metal and the 'Holey'-host: Synthesis, structural and magnetic characterisation of Co(II), Ni(II) and Mn(II) metal-organic frameworks incorporating 4,4'-dicarboxy-2,2'-bipyridine

We report herein the single crystal structures of four metal-organic framework complexes incorporating the 4,4'-dicarboxy-2,2'-bipyridine ligand, H(2)dcbp: alpha-[Co(dcbp)(H(2)O)(2)], 1; beta-[Co(dcbp)(H(2)O)(2)], 2, [Ni(dcbp)(H(2)O)(2)], and [[Mn(dcbp)].1/2DEF], 4 (DEF = diethylformamide). In each complex the ligand is deprotonated giving neutral species with 1:1 stoichiometry that form three-dimensional coordination polymers. Supramolecular isomerism (polymorphism) in 1 and 2 arises from the different ligand connectivity around the octahedral Co(II) centres. The two coordinated water molecules in 1 occupy cis positions, which are trans to the chelating bipyridine nitrogen atoms, leaving the carboxylate oxygen atoms in axial trans positions. In 2 all like donors occupy cis positions. Different modes of carboxylate coordination in 1 and 2 give dissimilar network topologies. A rare example of two interpenetrating 6(4)8(2)-b (quartz-like) chiral networks in 1 results from both dcbp carboxylate groups coordinating in a monodentate fashion to adjacent Co(II) centres, whereas in 2 only one carboxylate group bridges between adjacent Co(II) centres giving rise to a single chiral (10,3)-a net. In 1 and 2 the coordinated water molecules hydrogen bond to the non-coordinated carboxylate oxygen atoms. These interactions give rise to water-carboxylate double helices in , and support the coordination network in 2. Strikingly for a pair of dimorphs the crystal densities of 1 and 2 differ by ca. 0.3 g cm(-3)(1.654 vs. 1.940 g cm(-3), respectively). Compound 3 is isomorphous with 1 and likewise features two chiral interpenetrating nets of quartz topology. In 4, chelating bipyridine nitrogen atoms and four carboxylate oxygen atoms from a total of five adjacent dcbp ligands provide distorted octahedral geometry around Mn(II). The carboxylate groups bridge adjacent Mn(II) centres to produce bis-carboxylato chains which cross-link and generate a 3D network that is perforated with channels. The channels are occupied with disordered DEF molecules. The network topology in 4 is quite different to 1-3 and has a (4.6(2))(4(2).6)(4(3).6(6).8(6)) Schlafli notation. Magnetic susceptibility studies performed on 1, 2, [[Mn(dcbp)].1/2DMF] 5 (DMF = dimethylformamide) and [[Mn(dcbp)].2H(2)O] 6 reveal very weak antiferromagnetic coupling between the metal centres in each case.     

Imine Derivatives of Fumaraldehyde From Oxidation of A β-Aziridinyl Alcohol

Oxidation of a β-aziridinyl alcohol with tetrapropylammonium perruthenate yields a pyrrole and two unusual imine derivatives of fumaraldehyde.     

The diffraction of elastic waves by an imperfect fusion bond

We consider diffraction by a semi-infinite crack located alonga fusion interface between two differing elastic media. Twotypes of crack, namely open and partially closed cracks, areinvestigated. An open crack is modelled by a stress-free contactboundary condition and a partially closed crack is modelledby a spring contact boundary condition. For the latter, thejump in the stress across the crack is assumed to be proportionalto the jump in the displacement across the crack. This situationarises in, for example, a K-weld where the fine grain of theparent material (for example, ferritic or forged austeniticsteel) is in stark contrast with the coarse-grained weld metal(for example, austenitic weld metal). In the metal weld thedirection of the grain axis varies through the metal. However,diffraction is a local phenomenon and so the austenitic steelis assumed to have a zonal axis so that it may be modelled bya transversely isotropic composite. The ferritic or forged austeniticsteel will be modelled as an isotropic material.     

Observation of turbulent-driven shear flow in a cylindrical laboratory plasma device

An azimuthally symmetric radially sheared plasma fluid flow is observed to spontaneously form in a cylindrical magnetized helicon plasma device with no external sources of momentum input. A turbulent momentum conservation analysis shows that this shear flow is sustained by the Reynolds stress generated by collisional drift turbulence in the device. The results provide direct experimental support for the basic theoretical picture of drift-wave-shear-flow interactions.     

EPR-NMR Signal Enhancement with a Small Computer

A Digital Equipment Corporation PDP 8/S Computer is interfaced with an EPR Spectrameter to achieve signal enhancement.

A computer-based system for spectrum accumulation and noise averaging of EPR or NMR signals has been designed and implemented. The computer-based system was chosen over other perhaps more conventional systems because of its greater flexibility in the processing of spectra, especially after the accumulation is complete.(1)     

ON AVOIDANCE ACTIVITIES IN FISHERY ENFORCEMENT MODELS

Compliance and enforcement in fisheries are important issues from an economic point of view since management measures are useless without a certain level of enforcement. These conclusions come from the well‐established theoretical literature on compliance and enforcement problems within fisheries and a common result is that, it is efficient to set fines as high as possible and monitoring as low as possible, when fines are costless and offenders are risk neutral. However, this result is sensitive to the assumption that fishermen cannot engage in avoidance activities, e.g., activities to reduce the likelihood of being detected when noncomplying. The paper presents a model of fisheries that allows the fishermen to engage in avoidance activities. The conclusions from the model are that, under certain circumstances, fines are costly transfers to society since they not only have a direct positive effect on the level of deterrence, but also an indirect negative effect in the form of increased avoidance activities to reduce the probability of detection. The paper contributes to the literature on avoidance activities by introducing the externality from the illegal behavior as an endogenous effect on other offenders. For an externality, that has an exogenous effect on other actors, Malik shows that fines are only costly transfers for conditional deterrence (when one actor is deterred while another actor is not). For fisheries, we show that fines are also costly transfers under no deterrence (when no agents are deterred).