Search

Acknowledgements. This work was supported by the Spanish Ministry of Science and Innovation (project PID2020-115429GB-I00), by the Andalusian Regional Ministry of Economy, Knowledge, Business and University (PAI group SEJ-532 and project UMA18-FEDERJA-024, also supported by FEDER funding), and by the University of Malaga (project B1-2020 18). Sandra Gonzalez-Gallardo is recipient of a research contract within “Ayudas para la Recualificación del Sistema Universitario Español, Modalidad Margarita Salas”, financiado por la Unión Europea – NextGenerationEU., In this paper, we propose a theoretical framework that combines econometric and multiobjective programming methodologies to help researchers to identify and achieve optimal solutions to socio-economic and management problems. Sometimes, it is important to analyse which combination of values of the explanatory variables -in an econometric model- would imply the simultaneous achievement of the best values of the response variables. In such situations, if certain degree of conflict is observed among the response variables, we propose to formulate a multiobjective optimization problem based on the conclusions obtained from a regression analysis. Subsequently, the application of multiobjective optimization techniques allows gaining a better insight about the conflicting relation between the response variables, and how a balanced “optimal” situation among them could be achieved. This piece of information can be hardly extracted just by econometric techniques. An application in the field of economics of education, related to the analysis of the students’ well-being as a way to improve their academic performance, demonstrates the potential of our proposal., Spanish Ministry of Science and Innovation (project PID2020-115429GB-I00), Andalusian Regional Ministry of Economy, Knowledge, Business and University (PAI group SEJ-532 and project UMA18-FEDERJA-024, also supported by FEDER funding), University of Malaga (project B1-2020 18), “Ayudas para la Recualificación del Sistema Universitario Español, Modalidad Margarita Salas”, financiado por la Unión Europea – NextGenerationEU

Preference-based Evolutionary Multiobjective Optimization (EMO) algorithms approximate the region of interest (ROI) of the Pareto optimal front defined by the preferences of a decision maker (DM). Here, we propose a preference-based EMO algorithm, in which the preferences are given by means of aspiration and reservation points. The aspiration point is formed by objective values which the DM wants to achieve, while the reservation point is constituted by values for the objectives not to be worsened. Internally, the first generations are performed in order to generate an initial approximation set according to the reservation point. Next, in the remaining generations, the algorithm adapts the search for new non-dominated solutions depending on the dominance relation between the solutions obtained so far and both the reservation and aspiration points. This allows knowing if the given points are achievable or not; this type of information cannot be known before the solution process starts. On this basis, the algorithm proceeds according to three different scenarios with the aim of re-orienting the search directions towards the ROI formed by the Pareto optimal solutions with objective values within the given aspiration and reservation values. Computational results show the potential of our proposal in 2, 3 and 5-objective test problems, in comparison to other state-of-the-art algorithms.

In this article, we carry out a combined econometric and multiobjective analysis using data from a representative sample of Andalusian schools. In particular, four econometric models are estimated in which the students’ academic performance (scores in math and reading, and percentage of students reaching a certain threshold in both subjects, respectively) are regressed against the satisfaction of students with different aspects of the teaching-learning process. From these estimates, four objective functions are defined which have been simultaneously maximized, subject to a set of constraints obtained by analyzing dependencies between explanatory variables. This multiobjective programming model is intended to optimize the students’ academic performance as a function of the students’ satisfaction. To solve this problem we use a decomposition-based evolutionary multiobjective algorithm called Global WASF-GA with different scalarizing functions which allows generating an approximation of the Pareto optimal front. In general, the results show the importance of promoting respect and closer interaction between students and teachers, as a way to increase the average performance of the students and the proportion of high performance students.

Yıldız, Cem Burak ( Aksaray, Yazar ), Hauptgruppenanaloga von 1,3-Cyclobutandiylen faszinieren mit ihrer einzigartigen Reaktivitt und ihren elektronischen Eigenschaften. Bisher sind allerdings nur heteronukleare Vertreter isoliert worden. Wir berichten hier ber die Isolierung und Charakterisierung von All-Silicium-1,3-Cyclobutandiylen als stabile Singulettspezies mit geschlossenschaliger Konfiguration aus den reversiblen Reaktionen von Cyclotrisilen c-Si3Tip4 (Tip = 2,4,6-Triisopropylphenyl) mit den N-heterocyclischen Silylenen c-[(CR2CH2)(NtBu)2]Si: (R = H oder Methyl) mit gesttigten Grundger sten. Bei erhçhten Temperaturen werden aus diesen Gleichgewichtsmischungen Tetrasilacyclobutene erhalten. Die analoge Reaktion mit dem ungesttigten N-heterocyclischen Silylen c-(CH)2- (NtBu)2Si: verluft direkt zum entsprechenden Tetrasilacyclobuten ohne Nachweis des angenommenen 1,3-Cyclobutandiyl-Zwischenprodukts

Azizoğlu, Akın (Balikesir Author), Main group analogues of cyclobutane-1,3-diyls are fascinating due to their unique reactivity and electronic properties. So far only heteronuclear examples have been isolated. Here we report the isolation and characterization of all-silicon 1,3-cyclobutanediyls as stable closed-shell singlet species from the reversible reactions of cyclotrisilenec-Si(3)Tip(4)(Tip=2,4,6-triisopropylphenyl) with the N-heterocyclic silylenesc-[(CR2CH2)(NtBu)(2)]Si: (R=H or methyl) with saturated backbones. At elevated temperatures, tetrasilacyclobutenes are obtained from these equilibrium mixtures. The corresponding reaction with the unsaturated N-heterocyclic silylenec-(CH)(2)(NtBu)(2)Si: proceeds directly to the corresponding tetrasilacyclobutene without detection of the assumed 1,3-cyclobutanediyl intermediate., Deutscher Akademischer Austausch Dienst (DAAD)

ChemCatChem celebrates the achievements of female-led research groups in the field of catalysis. With this initiative, we seek to highlight the breadth and depth of the best research developed by women, and to increase its visibility in the wider catalysis community. Women of Catalysis offers a resource to aid in improving the representation of female scientific talent on invited speaker lists, conference and editorial boards, and as leaders in research consortia.

To study the reasons of the low academic performance of students in Spain, authorities must consider emotional dimensions, such as well-being, which directly affect their learning achievement. Furthermore, it would be interesting to compare Spanish students with students from Finland, which stand out in international rankings. We analyze how to promote students’ well-being in Spain as a mechanism to enhance their academic achievement. Using data from PISA 2018, four indicators are used to measure well-being according to variables describing the students’ context. By means of econometric techniques, interval multiobjective linear programming problems are formulated for Spain and Finland and solved through a new methodological scheme proposed in this paper, assuring the generation of possibly and necessarily efficient solutions in interval multiobjective linear programming. The purpose is to determine which aspects would allow the best possible well-being to be reached. We found several differences between the students achieving optimal compromise levels in each country, and we analyzed how the improvement of one indicator might affect the remaining aspects of well-being. Spanish students can further enhance their well-being compared to Finnish students. Furthermore, the lowest improvement rate is associated with the bullying index, especially in Finland, highlighting the need to promote anti-bullying measures.

In this paper, we propose a preference-based Evolutionary Multiobjective Optimization algorithm, at which the preferences are given in the form of desirable ranges for the objective functions, i.e. by means of aspiration and reservation levels. The aspiration levels are values to be achieved by the objectives, while the reservation levels are objective values not to be worsen. In the algorithm proposed, the first generations are performed using a set of weight vectors to initially converge to the region of the Pareto optimal front associated with the point formed with the reservation levels. At a certain moment, these weights are updated using the nondominated solutions generated so far, to re-direct the search towards the region which contains the Pareto optimal solutions with objective values among the desirable ranges. To this aim, the remaining number of generations are run using the updated weight vectors and the point formed with the aspiration levels. The computational experiment show the potential of our proposal in 2, 3 and 5-objective problems, in comparison to other state-of-the-art algorithms.

Carbon dioxide is readily fixed when reacting with either alumoxane dihydride [{MeLAl(H)}2(μ-O)] (1) or aluminum dihydride [MeLAlH2] (2) (MeL = HC[(CMe)N(2,4,6-Me3C6H2)]2-) to produce bimetallic aluminum formates [(MeLAl)2(μ-OCHO)2(μ-O)] (3) and [(MeLAl)2(μ-OCHO)2(μ-H)2] (5), respectively. Furthermore, [(MeLAl)2(μ-OCHO)2(μ-OH)2] (4) is easily obtained upon the reaction of 3 or 5 with H2O. The stability of the unusual dialuminum diformate dihydride core observed in 5 stems from the proximity of the Al centers allowing the formation of two Al-HAl bridges and precluding further hydride transfer to the HCO2 moieties. Contrary to this behavior, 1 and 2 react with CS2 giving cyclic alumoxane and aluminum sulfides [(MeLAl)2(μ-S)(μ-O)] (6) and [{MeLAl(μ-S)}2] (7), respectively. The molecular structures of 3-7 were characterized by IR, Raman, solution or solid-state (MAS) NMR spectroscopy and mass spectrometry and for 4-7 were characterized by X-ray diffraction studies. NMR kinetic studies and DFT calculations suggest that the mechanisms for the formation of 6 and 7 involve the transfer of a hydride group forming transient aluminum thioformate intermediates which proceed to form Al-S-Al moieties through the cleavage of C-S bonds and insertion of a sulfur atom, followed by the elimination of thioformaldehyde.

Carbon dioxide is readily fixed when reacting with either alumoxane dihydride [{MeLAl(H)}2(μ-O)] (1) or aluminum dihydride [MeLAlH2] (2) (MeL = HC[(CMe)N(2,4,6-Me3C6H2)]2-) to produce bimetallic aluminum formates [(MeLAl)2(μ-OCHO)2(μ-O)] (3) and [(MeLAl)2(μ-OCHO)2(μ-H)2] (5), respectively. Furthermore, [(MeLAl)2(μ-OCHO)2(μ-OH)2] (4) is easily obtained upon the reaction of 3 or 5 with H2O. The stability of the unusual dialuminum diformate dihydride core observed in 5 stems from the proximity of the Al centers allowing the formation of two Al-HAl bridges and precluding further hydride transfer to the HCO2 moieties. Contrary to this behavior, 1 and 2 react with CS2 giving cyclic alumoxane and aluminum sulfides [(MeLAl)2(μ-S)(μ-O)] (6) and [{MeLAl(μ-S)}2] (7), respectively. The molecular structures of 3-7 were characterized by IR, Raman, solution or solid-state (MAS) NMR spectroscopy and mass spectrometry and for 4-7 were characterized by X-ray diffraction studies. NMR kinetic studies and DFT calculations suggest that the mechanisms for the formation of 6 and 7 involve the transfer of a hydride group forming transient aluminum thioformate intermediates which proceed to form Al-S-Al moieties through the cleavage of C-S bonds and insertion of a sulfur atom, followed by the elimination of thioformaldehyde.

In this paper, a new version of the aggregation-based evolutionary algorithm Global WASF-GA (GWASF-GA) for many-objective optimization is proposed, called Adaptive Global WASF-GA (A-GWASF-GA). The fitness function of GWASF-GA is defined by an achievement scalarizing function (ASF) based on the Tchebychev distance, which considers two reference points (the nadir and utopian points) and a set of weight vectors. Despite of the benefits of using these two reference points simultaneously and a well-distributed set of weight vectors, it is necessary to go a step further to get better approximations in problems with complicated Pareto optimal fronts. For this, in A-GWASF-GA, some of the weight vectors are re-calculated during the optimization process based on the sparsity of the solutions found so far, and taking into account some theoretical results demonstrated in this paper regarding the ASF considered. Different strategies are carried out to accelerate the convergence and to maintain the diversity. The computational results, carried out in comparison with RVEA, NSGA-III, and different versions of MOEA/D, show the potential of A-GWASF-GA in well-known but also in novel many-objective optimization benchmark problems.

The convergence and the diversity of the decompositionbased evolutionary algorithm Global WASF-GA (GWASF-GA) relies on a set of weight vectors that determine the search directions for new non-dominated solutions in the objective space. Although using weight vectors whose search directions are widely distributed may lead to a well-diversified approximation of the Pareto front (PF), this may not be enough to obtain a good approximation for complicated PFs (discontinuous, non-convex, etc.). Thus, we propose to dynamically adjust the weight vectors once GWASF-GA has been run for a certain number of generations. This adjustment is aimed at re-calculating some of the weight vectors, so that search directions pointing to overcrowded regions of the PF are redirected toward parts with a lack of solutions that may be hard to be approximated. We test different parameters settings of the dynamic adjustment in optimization problems with three, five, and six objectives, concluding that GWASF-GA performs better when adjusting the weight vectors dynamically than without applying the adjustment. Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech.

Reactions of the tris(3,5-dimethylpyrazolyl)methanide amido complexes [M'{C(3,5-Me2 pz)3 }{N(SiMe3 )2 }] (M'=Mg (1 a), Zn (1 b), Cd (1 c); 3,5-Me2 pz=3,5-dimethylpyrazolyl) with two equivalents of the acidic Group 6 cyclopentadienyl (Cp) tricarbonyl hydrides [MCp(CO)3 H] (M=Cr (2 a), Mo (2 b)) gave different types of heterobimetallic complex. In each case, two reactions took place, namely the conversion of the tris(3,5-dimethylpyrazolyl)methanide ligand (Tpmd*) into the -methane derivative (Tpm*) and the reaction of the acidic hydride M = H bond with the M' = N(SiMe3 )2 moiety. The latter produces HN(SiMe3 )2 as a byproduct. The Group 2 representatives [Mg(Tpm*){MCp(CO)3 }2 (thf)] (3 a/b) form isocarbonyl bridges between the magnesium and chromium/molybdenum centres, whereas direct metal-metal bonds are formed in the case of the ions [Zn(Tpm*){MCp(CO)3 }](+) (4 a/b; [MCp(CO)3 ](-) as the counteranion) and [Cd(Tpm*){MCp(CO)3 }(thf)](+) (5 a/b; [Cd{MCp(CO)3 }3 ](-) as the counteranion). Complexes 4 a and 5 a/b are the first complexes that contain Zn - Cr, Cd - Cr, and Cd - Mo bonds (bond lengths 251.6, 269.8, and 278.9 pm, respectively). Quantum chemical calculations on 4 a/b* (and also on 5 a/b*) provide evidence for an interaction between the metal atoms.

A series of coinage metal complexes containing the redox-active metalloligands [RuCpX(κ3N-Tpmd)] {κ3N-Tpmd = κ3N-[C(pz)3] with pz = pyrazolyl; [RuCp(Tpmd)] (2a) and [RuCp*(Tpmd)] (2b)} are presented. 2a and 2b are isolable, relatively stable compounds, despite the fact that they feature a “naked” carbanion at the bridgehead position of the κ3N-coordinated tris(pyrazolyl)methanide ligand scaffold. As expected, both complexes act as κ1C ligands toward coinage metal fragments to yield dinuclear complexes of the general formula [RuCpX(μ-Tpmd){MX}] (μ-Tpmd = μ-κ1C:κ3N-[C(pz)3]; M = Au, X = Cl, CpX = C5H5 (3a) or C5Me5 (3b); M = Au, X = CN, CpX = C5H5 (4a) or C5Me5 (4b); M = Cu, X = OC(O)Me, CpX = C5H5 (5a); M = Cu, X = Si(SiMe3)3, CpX = C5H5 (6a) or C5Me5 (6b); M = Ag, X = SC(S)NEt2, CpX = C5H5 (7a), M = Au, X = C≡C–Ar, CpX = C5H5 {Ar = C6H5 (8a), 4-NH2-C6H4 (9a), 3,5-(CF3)2-C6H3 (10a)}). All complexes under study were fully characterized by common spectroscopic techniques; the structural parameters of 2a, 3a,...

Reactions of HC(pz)3 and HC(4-Mepz)3 with MgBu2 and Mg{N(SiMe3)2}2 gave the zwitterionic complexes [Mg{C(pz)3}2] (2) and [Mg{C(4-Mepz)3}2] (4), respectively, containing “free” pyramidal carbanions (pz = pyrazolyl). The solid-state structure of 2 has been determined. Reactions of 2 and 4 as well as the recently reported homo- and heteroleptic complexes [Mg{C(3, 5-Me2pz)3}2] (1) and [Mg{C(3, 5-Me2pz)3}{C(pz)3}] (3) with the Lewis acid AlEt3 furnished the bi- and trimetallic complexes [Mg{C(pz)3}2(AlEt3)2] (5), [Mg{C(pz)3}(AlEt3){C(3, 5-Me2pz)3}] (6), and [Mg{C(4-Mepz)3}2(AlEt3)2] (7). Based on NMR spectroscopic investigations, including an X-ray structural analysis on single crystals of 5, only the parent tris(pyrazolyl)methanide {C(pz)3}– and the 4-methyl-substituted ligand scaffolds form C-bound adducts with the Lewis acid. By quantifying the steric bulk of κ3N-coordinated {C(pz)3}– it could be shown that its steric features are similar to those of bulky phosphine ligands.

[D(CH2CH2S)2]M(XCH2CH2Y) 1–8 (M = Ge, Sn; D = O, S; X = Y = S, O and X = S, Y = O) spirocycles were synthesized to analyze the influence of the metal center replacement and the donor atom hardness on the strength of the transannular bond and the hypercoordination phenomena. The compounds were characterized by IR, Raman and NMR (1H, 13C and 119Sn) spectroscopy, E.I. mass spectrometry and elemental analysis. The molecular and crystal structures of compounds 3, 4, 6–8 and Ge(SCH2CH2S)2 (9) were obtained by X-ray diffraction analyses. They all exhibit five-coordinate central atoms due to transannular metal coordination (M ⋯ D) except 4, which displays a dimeric structure formed by the fusion of two five-membered rings resulting in a cyclic-distannoxane unit, {[O(CH2CH2S)2]Sn(SCH2CH2O)}2. The relationship between the nature of the metal center and the differences found between the two germanium and tin series are discussed.

The synthesis and structural characterization of the linear, cationic complex [{(DDP)Ga} 2 CUI[OTf]·2C 6 H 5 F (2, Tf = 0 2 SCF 3 ) stabilized by the monodentate, gallium-based ligand Ga(DDP) (DDP = [HC{(CMe)N(2,6-jPr 2 C 6 H 3 )} 2 ] - ), as well as NMR spectroscopic evidence for the formation of the corresponding silver compound [{(DDP)Ga} 2 Ag][Al(hfip) 4 ] (3, hfip = [OC(H)(CF 3 ) 2 ]), are reported. The remarkable steric properties of this gallium-based ligand permit the stabilization of 2, which exhibits an unusual linear geometry and a coordination number of two.

Synthesis and X-ray structural determination of three phosphorus compounds are reported. (3b) is monoclinic P2(1)/c with a = 11.852(1), b = 12.825(1), c = 12.445(1) A, β = 103.693(1)o; (4a) and (4b) are monoclinic P2(1)/n with a = 12.1422(16), b = 9.0860(12), c = 14.845(2) A, β = 96.498(3)o for (4a), and a = 12.2714(16), b = 9.2812(12), c = 14.800(2) A, β = 97.176(2)o for (4b). They all exhibit distorted tetrahedral geometry about the P atom. Ph2P(X)NHC7H7 (X=S (4a) and X=Se (4b)) show typical P–S and P–Se double bond distances and P–N single bonds, while P–S bond in 1-Ad2P(S)Cl (3b) is comparable to P–S single bonded probably due to the largeness of 1-adamantyl groups. Synthesis and X-ray structural determination of 1-Ad2P(S)Cl (3b), Ph2P(S)NHC7H7 (4a) and Ph2P(Se)NHC7H7 (4b) are reported.

The cyclic alumosiloxane [{LAl(μ-O)(Ph(2)Si)(μ-O)}(2)] (3) and alumosilicate [{LAl(μ-O){((t)BuO)(2)Si}(μ-O)}(2)] (4) were obtained by reaction of the appropriate R(2)Si(OH)(2) precursor (R = Ph, O(t)Bu) with [{LAl(H)}(2)(μ-O)] (1), providing a nice illustration of the Loewenstein rule at work at the molecular level.

Syntheses of the heavy chalcogen-containing alumoxanes [(Me)LAl(SeH)]2(μ-O) (4) and ((Me)LAl)2(μ-Te)(μ-O) (7) were accomplished by the reaction of ((Me)LAlH)2(μ-O) (2; (Me)L = HC[(CMe)N(2,4,6-Me3C6H2)]2(-)) with either red selenium or metallic tellurium. The aluminum hydrogenselenide [(Me)LAl(SeH)]2(μ-Se) (3) was also prepared from the reaction of red selenium and (Me)LAlH2 (1). All compounds were characterized by spectroscopic methods and X-ray diffraction studies. Density functional theory calculations were performed on 4 and 7.

In the last few decades, spectacular discoveries in the chemistry of the heavier main group elements appeared. One important development in the late 1980s and 1990s was the synthesis of a wide range of novel singlet biradicaloids, which can be regarded as stable and isolable analogs of reactive organic biradicals. More than 20 years after the first member of this family has been published, several contributions to this area have impressively extended the spectrum of these main group biradicaloids. This range includes fascinating electronic properties as well as closed-shell and radical-type reactivities. All these aspects can mainly be attributed to the inclusion of heavier main group elements into the biradicaloid scaffolds providing the essential electronic and structural flexibility. In this comprehensive chapter, early findings and recent developments in this area are presented. Particular attention is drawn on synthetically accessible systems, in which both radical sites are located in close spatial proximity as found in small rings and cages.

Recent developments in the field of metal-rich low valent metal complexes with gallium(I)/zinc(I) ligands and their structural features are reviewed together with related theoretical calculations. Some emphasis is given to sterically encumbering NHC analogous ligands as well as the naked ions E+. The chemistry of organo Zn(I) ligands at transition metals is reviewed in the light of the recently discovered synthetic approach via suitable organo Ga(I) complexes as starting materials.

The activation of the C≡N moiety in the redox-active metalloligand [CpRu{κ(3)N(pz)-1}][PF6] (2) (1: ambidentate hybrid ligand, N≡C-C(pz)3, with pz = pyrazolyl) was observed in the reaction with [Ir(cod)Cl]2 (cod = 1,5-cyclooctadiene). By performing detailed NMR spectroscopic and X-ray crystallographic investigations the product was found to be a bimetallic Ru(II)-Ir(III) complex of the composition [CpRu{μ-1}Ir(cod)Cl2][PF6] (3) consisting of a chemically modified ligand 1'. Most notably, the heterobimetallic complex 3 features an unprecedented metallacyclic alkyl-amido carbene (MCAAC) core structure, which is coordinated to an Ir(III) centre. Density functional theory (DFT) calculations as well as cyclic voltammetry (CV) studies were performed in an effort to establish the formal oxidation states of the metal atoms in 3. Indeed, a quasi-reversible oxidation wave was detected at E(1/2)(0) = 0.36 V, which was attributed to the Ru(II)/Ru(III) redox couple, while two irreversible reduction processes were observed at very negative potentials and have been assigned to the stepwise reduction of Ir(III) to Ir(I). First efforts to elucidate the reaction mechanism have also been performed.