Valence and spin situations in isomeric [(bpy)Ru(Q′)2]n (Q′ = 3,5-di-tert- butyl-N-aryl-1,2-benzoquinonemonoimine). An experimental and DFT analysis

The article deals with the ruthenium complexes, [(bpy)Ru(Q′)2] (1–3) incorporating two unsymmetrical redox-noninnocent iminoquinone moieties [bpy = 2,2′-bipyridine; Q′ = 3,5-di-tert-butyl-N-aryl-1,2-benzoquinonemonoimine, aryl = C6H5 (Q′1), 1; m-Cl2C6H3 (Q′2), 2; m-(OCH3)2C6H3 (Q′3), 3]. 1 and 3 have been preferentially stabilised in the cc-isomeric form while both the ct- and cc-isomeric forms of 2 are isolated [ct: cis and trans and cc: cis and cis with respect to the mutual orientations of O and N donors of two Q′]. The isomeric identities of 1–3 have been authenticated by their single-crystal X-ray structures. The collective consideration of crystallographic and DFT data along with other analytical events reveals that 1–3 exhibit the valence configuration of [(bpy)RuII(Q′Sq)2]. The magnetization studies reveal a ferromagnetic response at 300 K and virtual diamagnetic behaviour at 2 K. DFT calculations on representative 2a and 2b predict that the excited triplet (S = 1) state is lying close to the singlet (S = 0) ground state with singlet–triplet separation of 0.038 eV and 0.075 eV, respectively. In corroboration with the paramagnetic features the complexes exhibit free radical EPR signals with g [similar]2 and 1HNMR spectra with broad aromatic proton signals associated with the Q′ at 300 K. Experimental results in conjunction with the DFT (for representative 2a and 2b) reveal iminoquinone based preferential electron-transfer processes leaving the ruthenium(II) ion mostly as a redox insensitive entity: [(bpy)RuII(Q′Q)2]2+ (12+–32+) [leftrightharpoons] [(bpy)RuII(Q′Sq)(Q′Q)]+ (1+–3+) [leftrightharpoons] [(bpy)RuII(Q′Sq)2] (1–3) [leftrightharpoons] [(bpy)RuII(Q′Sq)(Q′Cat)]−/[(bpy)RuIII(Q′Cat)2]− (1−–3−). The diamagnetic doubly oxidised state, [(bpy)RuII(Q′Q)2]2+ in 12+–32+ has been authenticated further by the crystal structure determination of the representative [(bpy)RuII(Q′3)2](ClO4)2 [3](ClO4)2 as well as by its sharp 1H NMR spectrum. The key electronic transitions in each redox state of 1n–3n have been assigned by TD–DFT calculations on representative 2a and 2b

Phenological Study of 53 Spanish Minority Grape Varieties to Search for Adaptation of Vitiviniculture to Climate Change Conditions

The main phenological stages (budburst, flowering, veraison, and ripeness) of 53 Spanish minority varieties were studied to determine their potential to help winegrowers adapt to climate change conditions. In total, 43 varieties were studied in the same location in Spain (Alcalá de Henares, in the Madrid region) and 10 varieties in 5 other regions (Galicia, Navarre, Catalonia, Extremadura, and Andalusia). Other traits of agronomic and oenological interest, such as yield and acidity, were also monitored. The results allow for the grouping of the varieties into several clusters according to the time of ripeness (very early—only for red varieties—and early, intermediate, and late, for both red and white varieties) and yield (high, medium, and low). The total acidity in the grape juice ranged from 3 to 11 g of tartaric acid/L. The average temperatures were higher (up to 3–4 °C during summer) compared to historical averages during the 1957–2021 time period. Advanced phenology phases and reduced acidity are regarded as negative effects of climate change for winegrowing practices. Since some minority varieties showed late or intermediate ripening, high acidity, and high (1 Kg/shoot) or medium (0.5 Kg/shoot) yield, our findings suggest that they may be cultivated in the coming years by winegrowers as an approach to mitigate climate change effects.info:eu-repo/semantics/publishedVersio

Phenological Study of 53 Spanish Minority Grape Varieties to Search for Adaptation of Vitiviniculture to Climate Change Conditions

The main phenological stages (budburst, flowering, veraison, and ripeness) of 53 Spanish minority varieties were studied to determine their potential to help winegrowers adapt to climate change conditions. In total, 43 varieties were studied in the same location in Spain (Alcalá de Henares, in the Madrid region) and 10 varieties in 5 other regions (Galicia, Navarre, Catalonia, Extremadura, and Andalusia). Other traits of agronomic and oenological interest, such as yield and acidity, were also monitored. The results allow for the grouping of the varieties into several clusters according to the time of ripeness (very early—only for red varieties—and early, intermediate, and late, for both red and white varieties) and yield (high, medium, and low). The total acidity in the grape juice ranged from 3 to 11 g of tartaric acid/L. The average temperatures were higher (up to 3–4 °C during summer) compared to historical averages during the 1957–2021 time period. Advanced phenology phases and reduced acidity are regarded as negative effects of climate change for winegrowing practices. Since some minority varieties showed late or intermediate ripening, high acidity, and high (1 Kg/shoot) or medium (0.5 Kg/shoot) yield, our findings suggest that they may be cultivated in the coming years by winegrowers as an approach to mitigate climate change effects.Project RTI2018-101085-R-C31, “Valorization of Minority Grapevine Varieties for their Potential for Wine Diversification and Resilience to Climate Change (MINORVIN),” funded by MCIN/AEI/10.13039/501100011033, and by the ERDF, A Way to Make Europe.Peer reviewe

Controlling metal–ligand–metal oxidation state combinations by ancillary ligand (L) variation in the redox systems [L<SUB>2</SUB>Ru(&#956;-boptz)RuL<SUB>2</SUB>]<SUP>n</SUP>, boptz=3,6-bis(2-oxidophenyl)-1,2,4,5-tetrazine, and L=acetylacetonate, 2,2'-bipyridine, or 2-phenylazopyridine

The new compounds [(acac)2Ru(&#956;-boptz)Ru(acac)2] (1), [(bpy)2Ru(&#956;-boptz)Ru(bpy)2](ClO4)2 (2-(ClO4)2), and [(pap)2Ru(&#956;-boptz)Ru(pap)2](ClO4)2 (3-(ClO4)2 were obtained from 3,6-bis(2-hydroxyphenyl)-1,2,4,5-tetrazine (H2boptz), the crystal structure analysis of which is reported. Compound 1 contains two antiferromagnetically coupled (J=-36.7 cm-1) RuIII centers. We have investigated the role of both the donor and acceptor functions containing the boptz2- bridging ligand in combination with the electronically different ancillary ligands (donating acac-, moderately &#960;-accepting bpy, and strongly &#960;-accepting pap; acac=acetylacetonate, bpy=2,2'-bipyridine pap=2-phenylazopyridine) by using cyclic voltammetry, spectroelectrochemistry and electron paramagnetic resonance (EPR) spectroscopy for several in situ accessible redox states. We found that metal–ligand–metal oxidation state combinations remain invariant to ancillary ligand change in some instances; however, three isoelectronic paramagnetic cores Ru(&#956;-boptz)Ru showed remarkable differences. The excellent tolerance of the bpy co-ligand for both RuIII and RuII is demonstrated by the adoption of the mixed-valent form in [L2Ru(&#956;-boptz)RuL2]3+, L=bpy, whereas the corresponding system with pap stabilizes the RuII states to yield a phenoxyl radical ligand and the compound with L=acac-contains two RuIII centers connected by a tetrazine radical-anion bridge

Valence-state analysis through spectroelectrochemistry in a series of quinonoid-bridged diruthenium complexes [(acac)<SUB>2</SUB>Ru(&#956;-L)Ru(acac)<SUB>2</SUB>]<SUP>n</SUP> (n=+2, +1, 0, -1, -2)

The quinonoid ligand-bridged diruthenium compounds [(acac)2Ru(&#956;-L2-)Ru(acac)2] (acac-=acetylacetonato=2,4-pentanedionato; L2-=2,5-dioxido-1,4-benzoquinone, 1; 3,6-dichloro-2,5-dioxido-1,4-benzoquinone, 2; 5,8-dioxido-1,4-naphthoquinone, 3; 2,3-dichloro-5,8-dioxido-1,4-naphthoquinone, 4; 1,5-dioxido-9,10-anthraquinone, 5; and 1,5-diimido-9,10-anthraquinone, 6) were prepared and characterized analytically. The crystal structure analysis of 5 in the rac configuration reveals two tris(2,4-pentanedionato)ruthenium moieties with an extended anthracenedione-derived bis(ketoenolate) p-conjugated bridging ligand. The weakly antiferromagnetically coupled {RuIII(&#956;-L2-)RuIII} configuration in 1-6 exhibits complicated overall magnetic and EPR responses. The simultaneous presence of highly redox-active quinonoid-bridging ligands and of two ruthenium centers capable of adopting the oxidation states +2, +3, and +4 creates a large variety of possible oxidation state combinations. Accordingly, the complexes 1-6 exhibit two reversible one-electron oxidation steps and at least two reversible reduction processes. Shifts to positive potentials were observed on introduction of Cl substituents (1&#8594;2, 3&#8594;4) or through replacement of NH by O (6&#8594;5). The ligand-to-metal charge transfer (LMCT) absorptions in the visible region of the neutral molecules become more intense and shifted to lower energies on stepwise reduction with two electrons. On oxidation, the para-substituted systems 1-4 exhibit monocation intermediates with intervalence charge transfer (IVCT) transitions of RuIIIRuIV mixed-valent species. In contrast, the differently substituted systems 5 and 6 show no such near infrared (NIR) absorption. While the first reduction steps are thus assigned to largely ligand-centered processes, the oxidation appears to involve metal-ligand delocalized molecular orbitals with variable degrees of mixing

Usual monodentate binding mode of 2,2'-dipyridylamine (L) in isomeric trans-(acac)<SUB>2</SUB>Ru<SUP>II</SUP>(L)<SUB>2</SUB>, trans-[(acac)<SUB>2</SUB>Ru<SUP>III</SUP>(L)<SUB>2</SUB>]ClO<SUB>4</SUB>, and cis-(acac)<SUB>2R</SUB>u<SUP>II</SUP>(L)<SUB>2</SUB> (acac = acetylacetonate). synthesis, structures, and spectroscopic, electrochemical, and magnetic aspects

The reaction of cis-Ru(acac)<SUB>2</SUB>(CH<SUB>3</SUB>CN)<SUB>2</SUB> (acac = acetylacetonate) with 2,2'-dipyridylamine (L) in ethanolic medium resulted in facile one-pot synthesis of stable [(acac)<SUB>2</SUB>Ru<SUP>III</SUP>(L)]ClO<SUB>4 </SUB>([1]ClO<SUB>4</SUB>), trans-[(acac)<SUB>2</SUB>Ru<SUP>II</SUP>(L)<SUB>2</SUB>] (2), trans-[(acac)<SUB>2</SUB>Ru<SUP>III</SUP>(L)<SUB>2</SUB>]ClO<SUB>4</SUB> ([2]ClO<SUB>4</SUB>), and cis-[(acac)<SUB>2</SUB>Ru<SUP>II</SUP>(L)<SUB>2</SUB>] (3). The bivalent congener 1 was generated via electrochemical reduction of [1]ClO<SUB>4</SUB>. Although in [1]<SUP>+</SUP> the dipyridylamine ligand (L) is bonded to the metal ion in usual bidentate fashion, in 2/[2]<SUP>+</SUP> and 3, the unusual monodentate binding mode of L has been preferentially stabilized. Moreover, in 2/[2]<SUP>+</SUP> and 3, two such monodentate L's have been oriented in the trans- and cis-configurations, respectively. The binding mode of L and the isomeric geometries of the complexes were established by their single-crystal X-ray structures. The redox stability of the Ru(II) state follows the order 1 &lt; 2 «3. In contrast to the magnetic moment obtained for [1]ClO<SUB>4</SUB>, μ = 1.84 μ<SUB>B</SUB> at 298K , typical for low-spin Ru(III) species, the compound [2]ClO<SUB>4</SUB> exhibited an anomalous magnetic moment of 2.71 μ<SUB>B</SUB> at 300 K in the solid state. The variable-temperature magnetic measurements showed a pronounced decrease of the magnetic moment with the temperature, and that dropped to 1.59 μ<SUB>B</SUB> at 3K . The experimental data can be fitted satisfactorily using eq 2 that considered nonquenched spin-orbit coupling and Weiss constant in addition to the temperature-independent paramagnetism. [1]ClO<SUB>4</SUB> and [2]ClO<SUB>4</SUB> displayed rhombic and axial EPR spectra, respectively, in both the solid and the solution states at 77K

Bis(acetylacetonato)ruthenium complexes of noninnocent 1,2-dioxolene ligands: qualitatively different bonding in relation to monoimino and diimino analogues

Coordination compounds [Ru(acac)2(Q)] (acac=acetylacetonate; Q=o-benzoquinone) were prepared as complexes 1 (Q=o-benzoquinone), 2 (Q=3-methoxy-o-benzoquinone), 3 (Q=4-methyl-o-benzoquinone), and 4 (Q=3,5-di-tert-butyl-o-benzoquinone). The structures of 1 and 2 were determined to reveal a RuIII/o-benzosemiquinone formulation, supported by analysis of experimental data (spectroscopy, magnetism of 1) and by DFT calculations. The S=1 ground state calculated for 1 stands in contrast to the spin-paired analogues with arylimino-o-benzosemiquinonato and diimino-o-benzoquinone ligands. The close contacts of about 5.3 Å possible between semiquinone O atoms of different molecules in the crystal allow for intermolecular spin-spin interactions and an overall complex magnetic behavior. One quasireversible oxidation and two reversible one-electron reductions yielded the corresponding molecular ions, which were characterized by UV-visible-NIR and EPR spectroelectrochemistry in terms of [RuIII(acac)2(Q°)]+, [RuIII(acac)2(Q2-)]-, and [RuII(acac)2(Q2-)]2- descriptions in agreement with DFT results. The use of acceptor-substituted 1,2-dioxolenes resulted in the isolation of ionic species Na[Ru(acac)2(Q)] (Na(5); Q=4-chloro-o-benzoquinone) and Na(6) (Q=4-nitro-o-benzoquinone), which were similarly investigated as compounds 1-4. Magnetic susceptibility and EPR results confirm an S=½ ground state based on ruthenium(III). The combined studies reveal a remarkable substituent sensitivity, and in comparison to recently analyzed Ru(acac)2 complexes with o-benzoquinone monoimine and diimine ligands, the all-O-donor-containing new systems are distinguished by a qualitatively different metal-ligand interaction based on closer intermolecular radical-radical contacts and on weaker intramolecular dπ-π interactions

Charged, but Found “Not Guilty”: Innocence of the Suspect Bridging Ligands [RO(O)CNNC(O)OR]^2– = L^2– in [(acac)₂Ru(μ-L)Ru(acac)₂]^<i>n</i>, <i>n</i> = +,0,–,2–

Neutral diastereoisomeric diruthenium­(III) complexes, <i>meso</i>- and <i>rac</i>-[(acac)₂Ru­(μ-adc-OR)­Ru­(acac)₂] (acac^– = 2,4-pentanedionato and adc-OR^2– = dialkylazodicarboxylato = [RO­(O)­CNNC­(O)­OR]^2–, R = <i>tert</i>-butyl or isopropyl), were obtained from electron transfer reactions between Ru­(acac)₂(CH₃CN)₂ and azodicarboxylic acid dialkyl esters (adc-OR). The <i>meso</i> isomer <b>3</b> with R = isopropyl was structurally characterized, revealing two deprotonated and N–N coupled carbamate functions in a reduced dianionic bridge with <i>d</i>_N–N = 1.440(5) Å. A rather short distance of 4.764 Å has been determined between the two oxidized, antiferromagnetically coupled Ru^III centers. The <i>rac</i> isomer <b>4</b> with R = isopropyl exhibited stronger antiferromagnetic coupling. While the oxidation of the neutral compounds was fully reversible only for <b>3</b> and <b>4</b>, two well-separated (10⁸ < <i>K</i>_<i>c</i> < 10¹⁰) reversible one-electron reduction steps produced monoanionic intermediates <b>1</b>^––<b>4</b>^– with intense (ε ≈ 3000 M^–1 cm^–1), broad (Δν_1/2 ≈ 3000 cm^–1) absorptions in the near-infrared (NIR) region around 2000 nm. The absence of electron paramagnetic resonance (EPR) signals even at 4 K favors the mixed-valent formulation Ru^II(adc-OR^2–)­Ru^III with innocently behaving bridging ligands over the radical-bridged alternative Ru^II(adc-OR^•–)­Ru^II, a view which is supported by the metal-centered spin as calculated by density functional theory (DFT) for the methyl ester model system. The second reduction of the complexes causes the NIR absorption to disappear completely, the EPR silent oxidized forms <b>3</b>^<b>+</b> and <b>4</b>^<b>+</b>, calculated with asymmetrical spin distribution, do not exhibit near infrared (NIR) activity. The series of azo-bridged diruthenium complex redox systems [(acac)₂Ru­(μ-adc-R)­Ru­(acac)₂]^<i>n</i> (<i>n</i> = +,0,–,2−), [(bpy)₂Ru­(μ-adc-R)­Ru­(bpy)₂]^<i>k</i> (<i>k</i> = 4+,3+,2+,0,2−), and [(acac)₂Ru­(μ-dih-R)­Ru­(acac)₂]^<i>m</i> (<i>m</i> = 2+,+,0,–,2–; dih-R^2– = 1,2-diiminoacylhydrazido­(2-)) is being compared in terms of electronic structure and identity of the odd-electron intermediates, revealing the dichotomy of innocent vs noninnocent behavior