Inter-annual and inter-seasonal variability of the Orkney wave power resource

The waters surrounding the Orkney archipelago in the north of Scotland are one of the key regions in the world suitable for exploitation of both wave and tidal energy resources. Accordingly, Orkney waters are currently host to 1.08 GW of UK Crown Estate leased wave and tidal energy projects, with a further 0.5 GW leased in the southern part of the adjacent Pentland Firth. Although several wave resource models exist of the region, most of these models are commercial, and hence the results not publicly available, or have insufficient spatial/temporal resolution to accurately quantify the wave power resource of the region. In particular, no study has satisfactorily resolved the inter-annual and inter-seasonal variability of the wave resource around Orkney. Here, the SWAN wave model was run at high resolution on a high performance computing system, quantifying the Orkney wave power resource over a ten year period (2003–2012), a decade which witnessed considerable inter-annual variability in the wave climate. The results of the validated wave model demonstrate that there is considerable variability of the wave resource surrounding Orkney, with an extended winter (December–January–February–March, DJFM) mean wave power ranging from 10 to 25 kW/m over the decade of our study. Further, the results demonstrate that there is considerably less uncertainty (30%) in the high energy region to the west of Orkney during winter months, in contrast to much greater uncertainty (60%) in the lower energy region to the east of Orkney. The DJFM wave resource to the west of Orkney correlated well with the DJFM North Atlantic Oscillation (NAO). Although a longer simulated time period would be required to fully resolve inter-decadal variability, these preliminary results demonstrate that due to considerable inter-annual variability in the NAO, it is important to carefully consider the time period used to quantify the wave power resource of Orkney, or regions with similar exposure to the North Atlantic. Finally, our study reveals that there is significantly less variability in the practical wave power resource, since much of the variability in the theoretical resource is contained within relatively few extreme events, when a wave device enters survival mode

Manganese tricarbonyl complexes with asymmetric 2 2‑iminopyridine ligands: toward decoupling steric and electronic 3 factors in electrocatalytic CO2 reduction

Manganese tricarbonyl bromide complexes incorporating IP (2-(phenylimino)pyridine) derivatives, [MnBr(CO)3(IP)], are demonstrated as a new group of catalysts for CO2 reduction, which represent the first example of utilization of (phenylimino)pyridine ligands on manganese centers for this purpose. The key feature is the asymmetric structure of the redox-noninnocent ligand that permits independent tuning of its steric and electronic properties. The α-diimine ligands and five new Mn(I) compounds have been synthesized, isolated in high yields, and fully characterized, including X-ray crystallography. Their electrochemical and electrocatalytic behavior was investigated using cyclic voltammetry and UV−vis−IR spectroelectrochemistry within an OTTLE cell. Mechanistic investigations under an inert atmosphere have revealed differences in the nature of the reduction products as a function of steric bulk of the ligand. The direct ECE (electrochemical−chemical−electrochemical) formation of a five-coordinate anion [Mn(CO)3(IP)]−, a product of two-electron reduction of the parent complex, is observed in the case of the bulky DIPIMP (2-[((2,6-diisopropylphenyl)imino)methyl]pyridine), TBIMP (2-[((2-tert-butylphenyl)imino)methyl]-pyridine), and TBIEP (2-[((2-tert-butylphenyl)imino)ethyl]pyridine) derivatives. This process is replaced for the least sterically demanding IP ligand in [MnBr(CO)3(IMP)] (2-[(phenylimino)methyl]pyridine) by the stepwise formation of such a monoanion via an ECEC(E) mechanism involving also the intermediate Mn−Mn dimer [Mn(CO)3(IMP)]2. The complex [MnBr(CO)3(IPIMP)] (2-[((2-diisopropylphenyl)imino)methyl]pyridine), which carries a moderately electron donating, moderately bulky IP ligand, shows an intermediate behavior where both the five-coordinate anion and its dimeric precursor are jointly detected on the time scale of the spectroelectrochemical experiments. Under an atmosphere of CO2 the studied complexes, except for the DIPIMP derivative, rapidly coordinate CO2, forming stable bicarbonate intermediates, with no dimer being observed. Such behavior indicates that the CO2 binding is outcompeting another pathway: viz., the dimerization reaction between the five-coordinate anion and the neutral parent complex. The bicarbonate intermediate species undergo reduction at more negative potentials (ca. −2.2 V vs Fc/Fc+ ), recovering [Mn(CO)3(IP)]− and triggering the catalytic production of CO

Optimal design of measurements on queueing systems

We examine the optimal design of measurements on queues with particular reference to the M/M/1 queue. Using the statistical theory of design of experiments, we calculate numerically the Fisher information matrix for an estimator of the arrival rate and the service rate to find optimal times to measure the queue when the number of measurements are limited for both interfering and non-interfering measurements. We prove that in the non-interfering case, the optimal design is equally spaced. For the interfering case, optimal designs are not necessarily equally spaced. We compute optimal designs for a variety of queuing situations and give results obtained under the $D-$- and $D_s$-optimality criteria

Sensitisation of Eu(III)- and Tb(III)- based luminescence by Ir(III) units in Ir/lanthanide dyads: evidence for parallel energy-transfer and electron-transfer based mechanisms

A series of blue-luminescent Ir(III) complexes with a pendant binding site for lanthanide(III) ions has been synthesized and used to prepare Ir(III)/Ln(III) dyads (Ln = Eu, Tb, Gd). Photophysical studies were used to establish mechanisms of Ir→Ln (Ln = Tb, Eu) energy-transfer. In the Ir/Gd dyads, where direct Ir→Gd energy-transfer is not possible, significant quenching of Ir-based luminescence nonetheless occurred; this can be ascribed to photoinduced electron-transfer from the photo-excited Ir unit (*Ir, 3MLCT/3LC excited state) to the pendant pyrazolyl-pyridine site which becomes a good electron-acceptor when coordinated to an electropositive Gd(III) centre. This electron transfer quenches the Ir-based luminescence, leading to formation of a charge-separated {Ir4+}•—(pyrazolyl-pyridine)•− state, which is short-lived possibly due to fast back electron-transfer (<20 ns). In the Ir/Tb and Ir/Eu dyads this electron-transfer pathway is again operative and leads to sensitisation of Eu-based and Tb-based emission using the energy liberated from the back electron-transfer process. In addition direct Dexter-type Ir→Ln (Ln = Tb, Eu) energytransfer occurs on a similar timescale, meaning that there are two parallel mechanisms by which excitation energy can be transferred from *Ir to the Eu/Tb centre. Time-resolved luminescence measurements on the sensitised Eu-based emission showed both fast and slow rise-time components, associated with the PET-based and Dexter-based energy-transfer mechanisms respectively. In the Ir/Tb dyads, the Ir→Tb energy-transfer is only just thermodynamically favourable, leading to rapid Tb→Ir thermally-activated back energy-transfer and non-radiative deactivation to an extent that depends on the precise energy gap between the *Ir and Tb-based 5D4 states. Thus, the sensitised Tb(III)-based emission is weak and unusually short-lived due to back energy transfer, but nonetheless represents rare examples of Tb(III) sensitisation by a energy donor that could be excited using visible light as opposed to the usually required UV excitation

Rhenium and Manganese α-diimine tricarbonyls as CO2 reduction catalysts: Insights from novel ligand design

Concerns over climate change and energy security combined with the commercial application of carbon capture technologies has led to increased interest in the use of CO2 reduction catalysts as a means to convert this captured waste into fuel. In order to accomplish this photocatalytic or electrocatalytic systems must be employed of which the Lehn type catalyst based on the original [ReCl(CO)3(bpy)] complex is highly suitable due its selective CO formation and high efficiency. The purpose of this project was to develop new understanding of Lehn type CO2 reduction catalysis and, in particular, to develop new families of catalysts integrating manganese in place of rhenium. Much of the research has focussed on the concept of decoupling – either decoupling electron withdrawing groups from the α-diimine or decoupling the electronic effects from the steric effects. A variety of rhenium and manganese complexes have been synthesised and studied using a variety electrochemical and spectroscopic methods. Initial research focussed upon developing our understanding of the photodecomposition of the manganese based Lehn type catalysts and it was determined that the complexes decay via CO elimination giving a large variety of decomposition products. This research led to the investigation of the electrocatalytic and photocatalytic properties of three rhenium bis(mestiylimino)-acenaphthene complexes which exhibited electrocatalytic activity but not photocatalytic activity. The major family of ligands studied were asymmetric imino pyridine ligands which due to the break of symmetry between the phenyl moiety and the diimine allow for sterically demanding groups to be incorporated into the complexes without changing the electronic properties of the complex. These complexes are ideal for ‘lab mouse’ investigations of systems that show sensitivity to both steric and electronic factors. It was observed that while the rhenium imino pyridine complexes behaved in a manner similar to bipyridine complexes the manganese variants exhibited behaviour more akin to what has been observed in manganese diazabutadiene catalysts. Attempts to provide quantitative analysis of catalyst performance led to the employment of many different techniques ranging from gas chromatography to line shape analysis of voltammograms, however, no satisfactory method of performing quantitative analysis could be found. The overall conclusion is that the manganese based Lehn type catalysts can be used effectively as homogeneous electrocatalysts but the photosensitivity prohibits practical use in photocatalytic systems. The asymmetric imino pyridine ligands have shown great potential for systematic investigation of CO2 reduction catalysts and offer enormous scope for further development, however it is necessary for the community to adopt and publicise standards for benchmarking new catalysts as the methods employed today are not ideal

Manganese Tricarbonyl Complexes with Asymmetric 2‑Iminopyridine Ligands: Toward Decoupling Steric and Electronic Factors in Electrocatalytic CO₂ Reduction

Manganese tricarbonyl bromide complexes incorporating IP (2-(phenylimino)­pyridine) derivatives, [MnBr­(CO)₃(IP)], are demonstrated as a new group of catalysts for CO₂ reduction, which represent the first example of utilization of (phenylimino)­pyridine ligands on manganese centers for this purpose. The key feature is the asymmetric structure of the redox-noninnocent ligand that permits independent tuning of its steric and electronic properties. The α-diimine ligands and five new Mn­(I) compounds have been synthesized, isolated in high yields, and fully characterized, including X-ray crystallography. Their electrochemical and electrocatalytic behavior was investigated using cyclic voltammetry and UV–vis–IR spectroelectrochemistry within an OTTLE cell. Mechanistic investigations under an inert atmosphere have revealed differences in the nature of the reduction products as a function of steric bulk of the ligand. The direct ECE (electrochemical–chemical–electrochemical) formation of a five-coordinate anion [Mn­(CO)₃(IP)]⁻, a product of two-electron reduction of the parent complex, is observed in the case of the bulky DIPIMP (2-[((2,6-diisopropylphenyl)­imino)­methyl]­pyridine), TBIMP (2-[((2-<i>tert</i>-butylphenyl)­imino)­methyl]­pyridine), and TBIEP (2-[((2-<i>tert</i>-butylphenyl)­imino)­ethyl]­pyridine) derivatives. This process is replaced for the least sterically demanding IP ligand in [MnBr­(CO)₃(IMP)] (2-[(phenylimino)­methyl]­pyridine) by the stepwise formation of such a monoanion via an ECEC­(E) mechanism involving also the intermediate Mn–Mn dimer [Mn­(CO)₃(IMP)]₂. The complex [MnBr­(CO)₃(IPIMP)] (2-[((2-diisopropylphenyl)­imino)­methyl]­pyridine), which carries a moderately electron donating, moderately bulky IP ligand, shows an intermediate behavior where both the five-coordinate anion and its dimeric precursor are jointly detected on the time scale of the spectroelectrochemical experiments. Under an atmosphere of CO₂ the studied complexes, except for the DIPIMP derivative, rapidly coordinate CO₂, forming stable bicarbonate intermediates, with no dimer being observed. Such behavior indicates that the CO₂ binding is outcompeting another pathway: viz., the dimerization reaction between the five-coordinate anion and the neutral parent complex. The bicarbonate intermediate species undergo reduction at more negative potentials (ca. −2.2 V vs Fc/Fc⁺), recovering [Mn­(CO)₃(IP)]⁻ and triggering the catalytic production of CO

Manganese Tricarbonyl Complexes with Asymmetric 2‑Iminopyridine Ligands: Toward Decoupling Steric and Electronic Factors in Electrocatalytic CO₂ Reduction

Manganese tricarbonyl bromide complexes incorporating IP (2-(phenylimino)­pyridine) derivatives, [MnBr­(CO)₃(IP)], are demonstrated as a new group of catalysts for CO₂ reduction, which represent the first example of utilization of (phenylimino)­pyridine ligands on manganese centers for this purpose. The key feature is the asymmetric structure of the redox-noninnocent ligand that permits independent tuning of its steric and electronic properties. The α-diimine ligands and five new Mn­(I) compounds have been synthesized, isolated in high yields, and fully characterized, including X-ray crystallography. Their electrochemical and electrocatalytic behavior was investigated using cyclic voltammetry and UV–vis–IR spectroelectrochemistry within an OTTLE cell. Mechanistic investigations under an inert atmosphere have revealed differences in the nature of the reduction products as a function of steric bulk of the ligand. The direct ECE (electrochemical–chemical–electrochemical) formation of a five-coordinate anion [Mn­(CO)₃(IP)]⁻, a product of two-electron reduction of the parent complex, is observed in the case of the bulky DIPIMP (2-[((2,6-diisopropylphenyl)­imino)­methyl]­pyridine), TBIMP (2-[((2-<i>tert</i>-butylphenyl)­imino)­methyl]­pyridine), and TBIEP (2-[((2-<i>tert</i>-butylphenyl)­imino)­ethyl]­pyridine) derivatives. This process is replaced for the least sterically demanding IP ligand in [MnBr­(CO)₃(IMP)] (2-[(phenylimino)­methyl]­pyridine) by the stepwise formation of such a monoanion via an ECEC­(E) mechanism involving also the intermediate Mn–Mn dimer [Mn­(CO)₃(IMP)]₂. The complex [MnBr­(CO)₃(IPIMP)] (2-[((2-diisopropylphenyl)­imino)­methyl]­pyridine), which carries a moderately electron donating, moderately bulky IP ligand, shows an intermediate behavior where both the five-coordinate anion and its dimeric precursor are jointly detected on the time scale of the spectroelectrochemical experiments. Under an atmosphere of CO₂ the studied complexes, except for the DIPIMP derivative, rapidly coordinate CO₂, forming stable bicarbonate intermediates, with no dimer being observed. Such behavior indicates that the CO₂ binding is outcompeting another pathway: viz., the dimerization reaction between the five-coordinate anion and the neutral parent complex. The bicarbonate intermediate species undergo reduction at more negative potentials (ca. −2.2 V vs Fc/Fc⁺), recovering [Mn­(CO)₃(IP)]⁻ and triggering the catalytic production of CO

Manganese Tricarbonyl Complexes with Asymmetric 2‑Iminopyridine Ligands: Toward Decoupling Steric and Electronic Factors in Electrocatalytic CO₂ Reduction

Manganese tricarbonyl bromide complexes incorporating IP (2-(phenylimino)­pyridine) derivatives, [MnBr­(CO)₃(IP)], are demonstrated as a new group of catalysts for CO₂ reduction, which represent the first example of utilization of (phenylimino)­pyridine ligands on manganese centers for this purpose. The key feature is the asymmetric structure of the redox-noninnocent ligand that permits independent tuning of its steric and electronic properties. The α-diimine ligands and five new Mn­(I) compounds have been synthesized, isolated in high yields, and fully characterized, including X-ray crystallography. Their electrochemical and electrocatalytic behavior was investigated using cyclic voltammetry and UV–vis–IR spectroelectrochemistry within an OTTLE cell. Mechanistic investigations under an inert atmosphere have revealed differences in the nature of the reduction products as a function of steric bulk of the ligand. The direct ECE (electrochemical–chemical–electrochemical) formation of a five-coordinate anion [Mn­(CO)₃(IP)]⁻, a product of two-electron reduction of the parent complex, is observed in the case of the bulky DIPIMP (2-[((2,6-diisopropylphenyl)­imino)­methyl]­pyridine), TBIMP (2-[((2-<i>tert</i>-butylphenyl)­imino)­methyl]­pyridine), and TBIEP (2-[((2-<i>tert</i>-butylphenyl)­imino)­ethyl]­pyridine) derivatives. This process is replaced for the least sterically demanding IP ligand in [MnBr­(CO)₃(IMP)] (2-[(phenylimino)­methyl]­pyridine) by the stepwise formation of such a monoanion via an ECEC­(E) mechanism involving also the intermediate Mn–Mn dimer [Mn­(CO)₃(IMP)]₂. The complex [MnBr­(CO)₃(IPIMP)] (2-[((2-diisopropylphenyl)­imino)­methyl]­pyridine), which carries a moderately electron donating, moderately bulky IP ligand, shows an intermediate behavior where both the five-coordinate anion and its dimeric precursor are jointly detected on the time scale of the spectroelectrochemical experiments. Under an atmosphere of CO₂ the studied complexes, except for the DIPIMP derivative, rapidly coordinate CO₂, forming stable bicarbonate intermediates, with no dimer being observed. Such behavior indicates that the CO₂ binding is outcompeting another pathway: viz., the dimerization reaction between the five-coordinate anion and the neutral parent complex. The bicarbonate intermediate species undergo reduction at more negative potentials (ca. −2.2 V vs Fc/Fc⁺), recovering [Mn­(CO)₃(IP)]⁻ and triggering the catalytic production of CO