A novel hexagonal honeycomb K–Cr-oxalate anionic network with layers separated by a five-coordinated Cu(II)–pypn complex (pypn = N,N′-bis(2-pyridylmethyl)-1,3-propanediamine). Synthesis,characterisation, spectroscopy and crystal structure of {[KCr(C2O4)3][Cu(pypn)(H2O)](H2O)4}

A novel hexagonal-based honeycomb compound with overall formula {[KCr(C₂O₄)₃][Cu(pypn)(H₂O)](H₂O)₄} is reported in which pypn is with the tetradentate ligand (N,N′-bis(2-pyridylmethyl)-1,3-propanediamine). The [KCr(C₂O₄)₃]^2? moiety forms a hexagonal honeycomb structure, while the five-coordinated [Cu(pypn)(H₂O)]²⁺ moiety is located in between the layers, partly filling the holes in the cavities. The synthesis, X-ray crystal structure and some spectroscopic properties are presented. The coordination of Cr(III) is octahedral, with a CrO₆ chromophore, and the K⁺ ion is in a KO₆ environment (K–O distances vary from 2.36 to 2.48 ?). The [KCr(C₂O₄)₃]^2? layers have the K⁺ ions in a Λ conformation, while the Cr(III) ions in the Δ conformation. The geometry around the Cu(II) is five-coordinated with four nitrogens from the chelating pypn ligand in a plane and the apical position being occupied by the oxygen atom of the coordinating water molecule. The packing of the cationic and the anionic layers appears to be of special interest.     

A dinuclear copper(II) compound of a bis(imidazole)-containing tripodal ligand: Crystal structure and EPR spectroscopic studies

The dinuclear compound, 1, with the molecular formula of [Cu₂(H₃L)₂(ClO₄)₂][Cu₂(H₃L)₂(MeCN)₂](ClO₄)₆ was prepared by the reaction of [bis-(1H-imidazol-2-yl)-methyl]-pyridin-2-yl-methylamine (H₃L) with copper(II) perchlorate. The asymmetric unit of the crystal structure of 1 contains two dinuclear units, [Cu₂(H₃L)₂(ClO₄)₂]²⁺ and [Cu₂(H₃L)₂(MeCN)₂]⁴⁺ (abbreviated as 1^ClO4 and 1^MeCN), respectively, and they are linked through hydrogen bonding between the oxygen atom from the axial coordinated perchlorate anions and one of the neighboring imidazole rings from 1^MeCN. EPR spectroscopic studies of 1 in MeOH by addition of bridging ligands including NaN₃ and NaOH were carried out and the reaction process was discussed.     

A method for analysing the reliability of a transmission grid

The paper describes a probabilistic method for transmission grid security evaluation. Power system security is the ability of the power system to withstand sudden disturbances such as short circuits. The method presented here uses event and fault trees and combines them with power system dynamic simulations. Event trees model the substation protection and trip operations after line faults. Different event tree end states (fault duration, circuit breaker trips) are simulated with power system dynamic analysis program. The dynamic analysis results (power system post-fault states) are then classified into secure, alert, emergency and system breakdown. The probabilities, minimal cut sets and grid level importance measures (Fussell-Vesely, risk increase and decrease factors) are calculated for the total and partial system breakdown. In this way, the relative importance of the substation devices regarding to the system breakdown can be reached. Also the more and less likely contributing factors to system breakdown are received. With this method, an existing 400 kV transmission grid with its line fault and device failure statistics is analysed.     

Formation of a silver(I) coordination compound, with a pyrazole-pyridine ligand, whose crystal lattice is composed of three different types of 1D chains

Reaction of silver nitrate with the ligand 2-(1-Methyl-1H-pyrazol-5-yl)pyridine (1-mpp) produces a supramolecular material comprising three different types of one-dimensional coordination polymers as a result of two distinct orientations of the nitrate anions (with a 50/50 ratio) in the crystal lattice.     

Comparison of approaches for estimating pipe rupture frequencies for risk-informed in-service inspections

This paper describes the comparative study of two approaches to estimate pipe leak and rupture frequencies for piping. One method is based on a probabilistic fracture mechanistic model while the other one is based on statistical estimation of rupture frequencies from a large database. In order to be able to compare the approaches and their results, the rupture frequencies of some selected welds have been estimated using both of these methods. This paper highlights the differences both in methods, input data, need and use of plant specific information and need of expert judgement. The study focuses on one specific degradation mechanism, namely the intergranular stress corrosion cracking. This is the major degradation mechanism in old stainless steel piping in BWR environment, and its growth is influenced by material properties, stresses and water chemistry.