1,721,260 research outputs found
Syntheses and studies on transition metal complexes involving phosphine ligands towards the syntheses of macrocyclic phosphines
No full textThe soft acyclic phosphathia ligands, Ph2P(CH2)2)nS(CH2)2PPh2 (n = 2, 3) and Ph2P(CH2)2S(o-C6H4)S(CH2)2PPh2 have been complexed to the relatively hard Cr(III) ion giving the species [CrX2(L)]PF6 (X = Cl, Br). The P2S2-donor macrocycle, Ph2[14]aneP2S2, has been reacted with Cr(III), Cu(I), Ag(I) and Au(I). A series of Au(I) complexes have been prepared with Ph2P(CH2)2S(o-C6H4)S(CH2)2PPh2 and the P2O2 ligand, Ph2P(CH2)2O(CH2)2O(CH2)2PPh2. Characterisation of these complexes includes electrospray mass spectrometry, elemental analyses, IR, UV-vis and NMR (1H, 31P) spectroscopies and in the cases of [Au(Ph2P(CH2)2O(CH2)2O(CH2)2PPh2)]PF6, [(AuBr)2(Ph2P(CH2)2S(o-C6H4)S(CH2)2PPh2)] and [(AuCl)2(Ph2P(CH2)2O(CH2)2PPh2)] structural characterisation has been achieved using single crystal X-ray crystallography. The structures show, in each case, an approximately linear P2 or PX (X = Cl, Br) coordination geometry at the Au(I) centres and reveal non-coordinating ether and thioether functionalities.A series of secondary phosphine complexes of Rh(III), trans-[RhCl2(L)4]PF6 (L = PPh2H, PCy2H) and trans-[RhCl2(L-L)2]PF6 (L-L = PhHP(CH2)2PHPh, PhHP(CH2)3PHPh), have been prepared. Electrospray mass spectrometry, elemental analyses, IR and NMR (1H, 31P) spectroscopies have been used to characterise these species and confirm the trans coordination geometry in solutions. The X-ray crystal structures of two dinuclear phosphinite species, [(PPhOH)2(PPh2O)Rh(μ-Cl)3Rh(PPh2OH)(PPh2O)2] and [(PPh2OH)(PPh2O)Cl(NCMe)Rh(μ-Cl)2PPh2OH)(PPh2O)(NCMe)].2thf, the former adopting a face bridged biotahedral geometry while the latter involves an edge shared bioctahedral core. Both structures show phosphinite and phosphinic acid ligands indicating the sensitivity of these Rh(III) complexes in solution.Mono- and bidentate primary and secondary phosphines and a series of ditertiary phosphine, arsine and stibine ligands have been coordinated to Mn(I) carbonyl halides. Multinuclear NMR (1H, 13C, 31P, 55Mn) spectroscopies have been used to probe the solution behaviour, in particular the Mn-donor atom bonding in these species, X-ray crystallographic studies on several examples, including [MnCl(CO)3{o-C6H4(PH2)2}], confirms the fac-tricarbonyl arrangement. A related series of cationic Mn(I) compounds have also been investigated. A strategy for the preparation of triphosphine macrocycles based upon Mn(I) templates has been studied. The stepwise introduction of suitable phosphine precursors to Mn(I) has been achieved and template mediated ring closure reactions investigated. Characterisation of the macrocyclic products has been conducted using electrospray mass spectrometry, solution IR and multinuclear NMR spectroscopies.</p
Synthesis and luminescent properties of hetero-bimetallic and hetero-trimetallic Ru( ii )/Au( i ) or Ir( iii )/Au( i ) complexes
Full text linkA series of Ru(ii) and Ir(iii) based photoluminescent complexes were synthesised that incorporate an ancillary 2,2′-bipyridine ligand adorned with either one or two pendant N-methyl imidazolium groups. These complexes have been fully characterised by an array of spectroscopic and analytical techniques. One Ir(iii) example was unequivocally structurally characterised in the solid state using single crystal X-ray diffraction confirming the proposed formulation and coordination sphere. These complexes were then transformed into their heterometallic, Au(i)-containing, analogues in two steps to yield either bi- or trimetallic complexes that integrate {Au(PPh3)}+ units. X-ray diffraction was used to corroborate the solid state structure of the hetero bimetallic complex, based upon a Ru(ii)–Au(i) species. The heterometallic complexes all displayed red photoluminescent features (λem = 616–629 nm) that were consistent with the parent Ru(ii) or Ir(iii) lumophores in each case. The modulation of the emission from the Ru(ii)–Au(i) complexes was much more strongly evident than for the Ir(iii)–Au(i) analogues, which is ascribed to the inherent differences in the specific triplet excited state character of the emitting states within each heterometallic species
Acoustic impedance matching using loop shaping PID controller design
No full textFor several decades Proportional-Integral-Derivative control (PID) has been successfully used for a wide variety of industrial processes and remains the most used method. Recent work concerning the tuning of PID control coefficients has been proven to provide both robust and near-optimal performance using a Frequency Loop Shaping (FLS) procedure. The FLS tuning method minimizes the difference between the actual and the desired target loop transfer function. Such a control design procedure is ideal for problems in which the desired closed loop frequency response is predetermined over a specific frequency band. This paper explores the possibilities and trade-offs of applying the FLS control strategy in Active Noise Control (ANC) problems. The use of the FLS design is ideal for the problem of noise suppression in ducts, because the required acoustic impedance for the elimination of reflecting sound waves in the one-dimensional case is well defined. Hence, by controlling locally the reflecting boundary structure, a global cancelation of the undesired noise can be accomplished
Viscoelastic locally resonant double negative metamaterials with controllable effective density and elasticity
No full textA metamaterial that is composed of solid viscoelastic elements with controllable properties is proposed in this Letter. This enables an adaptable and general acoustic metamaterial to be practically realised. An array of masses with a single elastic connection to a supporting viscoelastic structure, such as one that is dynamically equivalent to an array of Helmholtz resonators, only provides a system with negative effective mass. A local active control scheme applied to each of these masses can emulate additional elastic connections to the supporting structure. An array of masses with a suitable local control scheme can provide both the negative effective stiffness and mass required for negative refraction. The tuneable feedback control parameters determine the characteristics of the region of double negativity.<br/
Polycationic Ru(II) luminophores: syntheses, photophysics, and application in electrostatically driven sensitization of lanthanide luminescence
Full text linkA series of photoluminescent Ru(II) polypyridine complexes have been synthesized in a manner that varies the extent of the cationic charge. Two ligand systems (L1 and L2), based upon 2,2′-bipyridine (bipy) mono- or difunctionalized at the 5- or 5,5′-positions using N-methylimidazolium groups, were utilized. The resulting Ru(II) species therefore carried +3, +4, +6, and +8 complex moieties based on a [Ru(bipy)3]2+ core. Tetra-cationic [Ru(bipy)2(L2)][PF6]4 was characterized using XRD, revealing H-bonding interactions between two of the counteranions and the cationic unit. The ground-state features of the complexes were found to closely resemble those of the parent unfunctionalized [Ru(bipy)3]2+ complex. In contrast, the excited state properties produce a variation in emission maxima, including a bathochromic 44 nm shift of the 3MLCT band for the tetra-cationic complex; interestingly, further increases in overall charge to +6 and +8 produced a hypsochromic shift in the 3MLCT band. Supporting DFT calculations suggest that the trend in emission behavior may, in part, be due to the precise nature of the LUMO and its localization. The utility of a photoactive polycationic Ru(II) complex was then demonstrated through the sensitization of a polyanionic Yb(III) complex in free solution. The study shows that electrostatically driven ion pairing is sufficient to facilitate energy transfer between the 3MLCT donor state of the Ru(II) complex and the accepting 2F5/2 excited state of Yb(III)
Controller architectures for optimum performance in practical active acoustic metamaterials
No full textOver the last decade there has been significant interest in the design and production of acoustic metamaterials with physical qualities not seen in naturally occurring media. Progress in this area has been stimulated by the desire to create materials that exhibit novel behaviour when subject to acoustic waves,such as negative refraction or the appearance of band gaps in the frequency response of the material. Proposed designs range from locally resonant phononic crystals to arrays of Helmholtz resonators within ducts and past research has investigated both passive and active materials. Much of the research into active acoustic metamaterials remains theoretical, therefore to determine whether such materials are physically realisable and of potentially practical use it is important to understand the physical constraints that may arise in a produced active metamaterial. In this paper a 1-dimensional active acoustic metamaterial derived from a passive, Helmholtz resonator based design is considered where the applied control forces produce controllable double negative behaviour. The physical dimensions and active forces required to achieve the desired novel behaviour are explored for different architectures and any trade-offs that might have to be considered when producing a practically useful active metamaterial are identifie
Active elastic metamaterials with applications in vibration and acoustics
No full textElastic metamaterials provide a new approach to solving existing problems in vibration and acoustics. They have also been associated with novel concepts such as acoustic invisibility and subwavelength imaging. To be applied to many of the proposed applications a metamaterial would need to have the desired mass density and elastic moduli over a prescribed frequency band. Importantly active metamaterials provide a degree of adaptability. This paper will focus on extending a previous theoretical concept to a more realistic experimental design. This will include a consideration of the problems which arise when the theory and simulation are developed into an experimental demonstration, including the role which the control system dynamics play in the achievable performance. The adaptability of the bandwidth in which the properties achieve their desired values will also be investigated
Combined colourimetric and turn-on luminescence from a redox-switchable 2-aza-anthraquinone bridged dimetallic assembly
Full text linkA redox active 2-aza-anthraquinone unit was conjugated with 1,10-phenanthroline chelating units to give a dimetallic Ir(III) complex. The complex shows ‘switch on’ luminescence upon reduction of the azaanthraquinone bridge in turn revealing a highly visual colourimetric response
Experimental validation of a geometric method for the design of stable and broadband vibration controllers using a propeller blade test rig
No full textA systematic geometric design methodology to generate a stable controller for simultaneous local and remote attenuation that was previously proposed is experimentally validated on a structure. The local control path transfer function for this experimental system is non-minimum phase due to which the original broadband controller design would yield an unstable controller. Here a modified procedure for systems with local non- minimum phase dynamics is used to generate a stable controller. According to this method, reduction in vibration at local and remote points on a structure can be parameterised in terms of the available design freedom and a controller is realised in terms of the optimal selection of this using the minimum phase counterpart of the local control path transfer function. The modified method results in a controller that is both stable and stabilizing and which achieves the desired vibration attenuation at the local and remote points on the structure. An experimental facility that replicates the vibration transmission through the shaft of a propeller blade rig system is used to demonstrate the method. Vibration for excitation near the first bending mode frequency of the resonating part of this structure is attenuated at the non-resonating part of the system without deteriorating vibration at the resonating en
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