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Wireless sensor networks (WSNs) are composed of numerous nodes distributed in geographical regions. Security and energy efficiency are challenging tasks due to an open environment and a restricted battery source. The multiobjective trust‐aware artificial hummingbird algorithm (M‐TAAHA) is proposed to achieve secure and reliable transmission over a WSN with a mobile sink (MS). The M‐TAAHA selects secure cluster head (SCH) nodes based on trust, energy, interspace between sensors, interspace between SCH and MS, and the CH balancing factor. A secure route is found by M‐TAAHA with trust, energy, and interspace between SCH and MS. The M‐TAAHA avoids the malicious nodes to improve data delivery and avoid unwanted energy consumption. The M‐TAAHA is analyzed using energy consumption, alive nodes, life expectancy, delay, data packets received in MS, throughput, packet delivery ratio, and packet loss ratio. Existing techniques (LEACH‐TM, EATMR, FAL, Taylor‐spotted hyena optimization [Taylor‐SHO], TBEBR, and TEDG) are used for comparison with the M‐TAAHA. Findings show that the energy consumption of the proposed M‐TAAHA for 1000 rounds is 0.56 J (1.78 × smaller than that of the Taylor‐SHO).

The mining industry is known for its valuable minerals, and the way to get minerals is by mining below the surface. Many industries benefitted by adopting automation which has improved workplace operational management, enhanced safety, real-time monitoring, and cost-effectiveness. On the basis of challenges in underground mines, a reliable wireless communication and monitoring system is required in underground mines to enhance safety and prevent major hazards. Underground mine environments are affected by various environmental parameters such as toxic gases, flammable and inflammable gases, and dust. The variation in the presence of harmful gases is a major issue that causes gas explosions and damages the mine infrastructure. Currently, most underground mines adopted conventional multi-gas detectors to monitor mine gases manually at regular intervals or once a day. In this paper, a real-time data communication system to monitor mining parameters based on wireless ZigBee modules is established and evaluated in two different underground mines in India. A wireless message communication establishment process between two ZigBee modules is described in detail, and an investigation of radio range tests by measuring received signal strength indication (RSSI) parameters is carried out in the first underground mine site at level 3 with consideration of 10-m intervals apart at each test for the straight tunnel case. In addition, wireless communication is established to monitor the environmental parameters of underground mine levels to the surface. Further, established wireless communication to monitor the environmental parameters of the straight and curved tunnels of a second underground mine. The experimental result represents successful wireless communication between ZigBee modules with a distance of 100 m to 120 m in straight tunnels and a reduction in signal strength and data packet loss in curved tunnels of underground mines. In addition, the results show that the developed ZigBee-based system is suitable for measuring environmental parameters in open surface and underground mines.

The automation in the mining industry by adopting Internet of Things (IoT) technology is great potential to improve safety and efficiency. The mining industry is recognized globally for its valuable resources (gold, coal, iron ore, etc.) which are obtained by mining below the surface. The productivity and safety of mine personnel are impacted by several environmental parameters in underground mines, such as toxic gases, flammable gases, elevated levels of carbon dioxide (CO2), and decreased levels of oxygen (O2) concentrations. The presence of these gases is a significant issue and needs to be dealt with suitably. There are various methods to monitor the percentage of gases and provide a suitable course of action in case of an increase in the threshold limit of gases. Each system has its limitations. Wireless monitoring systems are indispensable in underground mines. This paper presents the methodology to adopt IoT in underground mines to measure environmental parameters in underground mine areas, the structure of installation of sensors in underground mines, threshold limits of gases, and underground mine disasters which were caused by gas explosion accidents. Further, it evaluates wireless sensor networks (WSNs) techniques ZigBee and LoRa for underground mines applications. Subsequently, it proposed a real-time industrial safety system in underground mines with its working, effectiveness, and scope are discussed.

The contribution of copper complexes of salen-based Schiff bases N,N′-bis(salicylidene)ethylenediamine (C1), N,N′-bis(4-hydroxysalicylidene)ethylenediamine (C2), and N,N′-bis(5-hydroxysalicylidene)ethylenediamine (C3) to the flame retardancy of thermoplastic polyurethane (TPU) is investigated in the context of minimizing the inherent flammability of TPU. Thermal and fire properties of TPU are evaluated. It is observed that fire performances vary depending upon the substitution of the salen framework. Cone calorimetry [mass loss calorimetry (MLC)] results show that, in TPU at 10 wt % loading, C2 and C3 reduce the peak of heat release rate by 46 and 50%, respectively. At high temperature, these copper complexes undergo polycondensation leading to resorcinol-type resin in the condensed phase and thus acting as intumescence reinforcing agents. C3 in TPU is particularly interesting because it delays significantly the time to ignition (MLC experiment). In addition, pyrolysis combustion flow calorimetry shows reduction in the heat release rate curve, suggesting its involvement in gas-phase action. Structural changes of copper complexes and radical formation during thermal treatment as well as their influence on fire retardancy of TPU in the condensed phase are investigated by spectroscopic studies supported by microscopic and powder diffraction studies. Electron paramagnetic resonance (EPR) spectroscopy was fully used to follow the redox changes of Cu(II) ions as well as radical formation of copper complexes/TPU formulations in their degradation pathways. Pulsed EPR technique of hyperfine sublevel correlation spectroscopy reveals evolution of the local surrounding of copper and radicals with a strong contribution of nitrogen fragments in the degradation products. Further, the spin state of radicals was investigated by the two-dimensional technique of phase-inverted echo-amplitude detected nutation experiment. Two different radicals were detected, that is, one monocarbon radical and an oxygen biradical. Thus, the EPR study permits to deeply investigate the mode of action of copper salen complexes in TPU.

Intumescent coatings are the present-day state-of-art techniques to protect steel structures and other structural materials from fire hazards. Thermal insulation properties of such protective materials are normally deduced from standard fire tests, however, with least reference to char integrity and strength. This work proposes a simple and resourceful in situ experimental protocol to evaluate char strength of intumescent coatings on steel panels during hydrocarbon time–temperature fire test (at about 1200°C). It is based on in-process monitoring the physical integrity, mechanical stability, and thermal insulation capacity of fully developed char under a stream of air (airjet) before steel plate reaches its critical temperature. A bench-scale furnace designed in our laboratory to reproduce hydrocarbon fire scenario (UL1709) was upgraded to simulate air turbulence to impact the char strength. Silicone- and epoxy-based coatings on steel panels were tested under these conditions. Silicone-based coatings are found to have several interesting advantages over the latter. Furthermore, this protocol was extended to investigate the compositional influence on char strength in a set of silicon-based coatings.

A broad spectrum of applications of “Salen”-based Schiff bases tagged them as versatile multifunctional materials. However, their applicability is often bounded by a temperature threshold and, thus, they have rarely been used for high temperature applications. Our investigation of a classical Schiff base, N,N′-bis(4-hydroxysalicylidene)ethylenediamine (L2), reveals that it displays an intriguingly combative response to an elevated temperature/fire scenario. L2 resists and regulates thermal degradation by forming an ablative surface, and acts as a thermal shield. A polycondensation via covalent cross-linking, which forms a hyperbranched cross-linked resin is found to constitute the origin of the ablative surface. This is a unique example of a resin formation produced with a Schiff base, that mimicks the operational strategy of a high-heat resistant phenolic resin. Further applicability of L2, as a flame retardant, was tested in an engineering polymer, polyamide-6. It was found that it reinforces the polymer against fire risks by the formation of an intumescent coating. This paves the way for a new strategic avenue in safeguarding polymeric materials toward fire risks. Further, this material represents a promising start for thermal protective applications.

AbstractLow temperature solution growth technique is a versatile and low cost technique to grow single crystals of good quality. Before crystal growth, it needs to decide solvent and growth temperature by studying solubility at different temperatures in different solvents, and pH of the growth solution. Metastable zone width and induction period are other important parameters considered during crystal growth. We have presented a simple, cost effective test to decide growth temperature, solution pH and proportion of different components (in case of multi-component compounds) of compound in the solution to grow quality single crystals with optimum growth rate. L-arginine phosphate monohydrate is a promising nonlinear optical crystal and we have successfully attempted to study the optimum pH and proportion of L-arginine and phosphoric acid in the solution for crystal growth by measuring ultrasonic velocity and determining related thermodynamic parameters.

A detailed investigation on the properties of the high‐temperature and low‐temperature modifications of the iron(II) spin‐crossover complex [FeL1(HIm)2] (1)and its isotopic deuterium‐labelled analogue [FeL1(DIm)2] (1D), and the pair [FeL2(azpy)]·MeOH/[FeL2(azpy)]·CD3OD/[FeL2(azpy)] (2·MeOH/2·CD3OD/2), in which L1 and L2 are tetradentate N2O22–‐coordinating Schiff base like ligands, L1 = {diethyl(E,E)‐2,2′‐[1,2‐phenylbis(iminomethylidyne)]bis[3‐oxobutanoate](2–)‐N,N′,O3,O3′}, L2 = {2,2′‐[1,2‐phenylbis(iminomethylidyne)]bis[1‐phenylbutane‐1,3‐dione](2–)‐N,N′,O3,O3′},HIm = imidazole, and azpy = 4,4′‐azopyridine, is presented. All complexes except 2show a cooperative spin transition with hysteresis widths between approximately 5 K (1LTand 1LTD), 70 K (1HT[9]and 1HTD, around room temperature), and 80 K (2·MeOH and 2·CD3OD). In all cases, an influence of the H/D exchange on the transition temperature and the hysteresis width is observed. For 1HT, first‐order reversal curves (FORCs) have been recorded, and a statistical analysis gives the interaction parameter J= 560 K, indicating strong intermolecular interactions. X‐ray structural analysis of the different samples (1HT[9]and 1HTD: HS; 1LTand 1LTD: LS; and 2·MeOH and 2·CD3OD: HS) gives a deeper insight into the molecular packing in the crystals and helps explain the increase of cooperative interactions during the spin transition. In all cases, one hydrogen bond involves an oxygen atom of the Schiff base like ligand that serves as a donor for the iron centre. The influence of this hydrogen bond on the ligand field strength of the iron centre is discussed and a new model is developed to explain the observed connection between hydrogen bonds and exceptionally wide hysteresis loops for the complexes presented in this work and other examples from the literature.

Stepping up: A two‐step magnetic spin transition with accompanying structural phase transitions is reported for the first time for FeIII. The transitions are observed at 187 K and 90 K on cooling with a hysteretic transition recorded upon heating during the first crossover at 106 K. The intermediate phase persists over 97 K and contains an unprecedented [HS‐HS‐LS] motif with tripling of the unit cell.

Stufenweise: Erstmals wird für FeIIIein zweistufiger magnetischer Spinübergang mit strukturellen Phasenübergängen beschrieben. Die Übergänge werden beim Abkühlen bei 187 K und 90 K beobachtet; beim Erwärmen tritt eine Hysterese während des ersten Crossovers bei 106 K auf. Die Zwischenphase ist über einen Bereich von 97 K persistent und enthält ein ungewöhnliches [HS‐HS‐LS]‐Motiv mit verdreifachter Elementarzelle.

A supramolecular engineering approach has been developed for a novel family of Nsalicylidene aniline derivatives to control their thermo and photochromic behaviours. Hsaltrz, Habs, Hsalphen, Hsaltz and Ksaltz are versatile molecules built from Nheterocycles, which drive the molecular arrangement to form a controlled crystal packing with predesigned optical properties. A complete structural, optical and computational study of powders of these new molecular nanoswitches is presented. An Nsalicylidene aniline derivative possessing no thermo or photoinduced chromic properties thanks to a specific molecular geometry was sought, and Habs and Hsalphen were designed to enhance π–π stacking interactions. A theoretical study of the crystal packing, combined with timedependent diffuse reflectance studies of Habs, have confirmed the appearance of photochromism at room temperature completed with an unprecedented “springtype effect” observed during the photochemical relaxation of the metastable transketo form. The absence of thermochromism in an Nsalicylidene aniline derivative, induced by the absence of cisketo form, is a unique behaviour, firstly identified and explained for these types of compounds. Finally, Hsaltz and Ksaltz are the result of a molecular derivation of Hsaltrz which allow enhancing the amplitude of thermochromism of these functional materials.

All light and no heat?Structure–property relationships for photochromic and thermochromic N‐salicylideneanils have been revised (see picture). One derivative has a packed crystal structure, is photochromic and exhibits an infinitely slow thermal back relaxation of technological interest. Complexation of the anils to transition metals has also been studied.

The preparation of a novel pentadentate binucleating compartmental ligand, 2-hydroxy-5-methylisophthalaldehyde bis(p-methoxy thiobenzoylhydrazone), is described together with the corresponding chloro-bridged cobalt(II), nickel(II), copper(II) and zinc(II) complexes, which were characterized based on spectral, magnetic, thermal and electrochemical studies. Cryomagnetic investigations (77–296 K) reveal a strong antiferromagnetic spin-exchange between the copper(II) ions (Jbased on H= -2JS1. S2is 305 cm-1). An electrochemical study of the copper(II) complex shows two distinct quasi-reversible redox peaks (E11/2= -0.4 and E21/2= -0.69 V vs saturated calomel electrode), indicating a stepwise reduction of the copper centers (CuIICuII? CuIICuIand CuIICuI? CuICuI). The EPR spectrum is typical of a “rhombic compressed local molecular environment”. The ligand and its copper and zinc complexes exhibit fluorescence at room temperature in DMF. All of the compounds under study were screened for antimicrobial action.

The binucleating ligand LH3, 2,6-diformyl-p-cresol-bis(phenylthioacetyldrazone), a Schiff base condensation product of 2,6-diformyl-p-cresol and phenylthioacetyldrazide forms complexes of the [M2ClL] type with CoII, NiIIand CuIIions, which were characterized by elemental analysis, magnetic susceptibility, electronic spectra, molar conductance, i.r., n.m.r., e.p.r., t.g. and FAB mass spectral measurements. Sub-normal magnetic moments indicate the operation of antiferromagnetic coupling between the metal centres. The ligand and its copper complex show a pronounced fungistatic activity.

Four binuclear transition metal(II) complexes: [Co2L(μ-Cl)Cl2] · 2H2O, [Ni2L(μ-Cl)Cl2(H2O)2] · 2H2O, [Cu2L(μ-Cl)Cl2] · 2H2O and [Zn2L(μ-Cl)Cl2] · 2H2O, where LH is the binucleating ligand 2,6-diformyl-4-methylphenol bis(2-hydrazino benzothiazole), were prepared. Based on the i.r. spectra, elemental analysis, conductivity measurements and thermal analysis, we propose that these complexes contain an endogenous phenoxide bridge and an exogenous chloride bridge. Magnetic and spectral data supports the existence of a weak antiferromagnetic interaction between the metal ions, and octahedral for NiIIand a square pyramidal environment for remaining complexes. The compounds show significant growth inhibitory activity against the fungi, Aspergillus nigerand Candida albicans, as compared to antibacterial activity against Bacillus cirroflagellosusand Pseudomonas auregenosa.

Oxovanadium (IV) complexes, [(VO)2L′(acac)] (where L′H3=thiosemicarbazones derived from 2,6-diformyl-p-cresol with thiosemicarbazides) have been synthesised and characterised using physico-chemical techniques. The complexes have a stoichiometry of 2:1 (M/L) wherein phenolic oxygen is coordinated to two metal atoms to form M–O–M bridge. Each metal atom exhibits a coordination number of five. The transition energies ΔE1and ΔE2obtained from the electronic absorption spectra of the VO2+-complex in conjunction with the spin-Hamiltonian parameters obtained from EPR data are used to evaluate the spin-orbit coupling constant, the dipolar and the Fermi-contact terms. The bonding coefficients α2and β2are evaluated from the available molecular-orbital theories and the experimental data. The various terms evaluated are correlated and the general behaviour of the VO2+ion in various ligand fields is discussed.

A novel dinucleating pentadentate Schiff base, resulting from the condensation of 2,6-diformyl-p-cresol and N-methyl-indolyl-3-thiohydrazide, and its Zn complex have been prepared and characterized on the basis of elemental analysis, IR, UV-Visible,1H NMR and13C NMR studies. The ligand is acyclic and consists of a phenolate head unit, with two inbuilt azomethine shoulders and two indole thiohydrazide arms forming SNONS coordinating sites. NMR and IR spectral studies show that the ligand exists in thioketo form. Each Zn ion in the dinuclear core is in tetrahedral environment with endogenous phenolate bridging and exogenous acetate bridging. The zinc complex in DMF exhibits fluorescence.

Review: 120 refs.

The cover picture showsa panel of functional Nsalicylidene derivatives that can be rationally designed and assembled by crystal engineering. The amplitude of their thermochromism andor photochromism can be finely tuned as shown by the central needle. This study is supported by a multidisciplinary approach syntheses, physical and structural studies, calculations. Details are discussed in the article by Y. Garcia et al. on p. 621 ff.

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