Electronic Structure of Ru26+ Complexes with Electron-Rich Anilinopyridinate Ligands

Diruthenium paddlewheel complexes supported by electron-rich anilinopyridinate (Xap) ligands were synthesized in the course of the first in-depth structural and spectroscopic interrogation of monocationic [Ru₂(Xap)₄Cl]⁺ species in the Ru₂⁶⁺ oxidation state. Despite paramagnetism of the compounds, ¹H NMR spectroscopy proved highly informative for determining the isomerism of the Ru₂⁵⁺ and Ru₂⁶⁺ compounds. While most compounds are found to have the polar (4,0) geometry, with all four Xap ligands in the same orientation, some synthetic procedures resulted in a mixture of (4,0) and (3,1) isomers, most notably in the case of the parent compound Ru₂(ap)₄Cl. The isomerism of this compound has been overlooked in previous reports. Electrochemical studies demonstrate that oxidation potentials can be tuned by the installation of electron donating groups to the ligands, increasing accessibility of the Ru₂⁶⁺ oxidation state. The resulting Ru₂⁶⁺ monocations were found to have the expected (π*)² ground state, and an in-depth study of the electronic transitions by Vis/NIR absorption and MCD spectroscopies with the aid of TD-DFT allowed for the assignment of the electronic spectra. The empty δ* orbital is the major acceptor orbital for the most prominent electronic transitions. Both Ru₂⁵⁺ and Ru₂⁶⁺ compounds were studied by Ru K-edge X-ray absorption spectroscopy; however, the rising edge energy is insensitive to redox changes in the compounds due to the broad line shape observed for 4d transition metal K-edges. DFT calculations indicate the presence of ligand orbitals at the frontier level, suggesting that further oxidation beyond Ru₂⁶⁺ will be ligand-centered rather than metal-centered.

Steric, Activation Method and Solvent Effects on the Structure of Paddlewheel Diruthenium Complexes

Conventional heating and solvothermal synthetic methods (with or without microwave activation) have been used to study the reaction of o-, m- and p-methoxybenzoic acid with [Ru2Cl(μ-O2CMe)4]. The tetrasubstituted series [Ru2Cl(µ-O2CC6H4-R)4], with R = o-OMe, m-OMe and p-OMe, has been prepared by the three procedures. Depending on the synthetic method and the experimental conditions, three compounds have been isolated (1a, 1b, 1c) with the o-methoxybenzoate ligand. However, with the m- and p-methoxybenzoate ligands, only the complexes 2 and 3 have been obtained, respectively. Compound 1a, with stoichiometry [Ru2Cl(µ-O2CC6H4-o-OMe)4]n, shows a polymeric structure with the chloride ions bridging the diruthenium units to form linear chains. Compounds 2 and 3, with the same stoichiometry, predictably form zig-zag chains in accordance with their insolubility and their magnetic measurements. Compound 1b, [Ru2Cl(µ-O2CC6H4-o-OMe)4(EtOH)], is a discrete molecular species with a chloride ion and one ethanol molecule occupying the axial positions of the dimetallic unit. Compound 1c is a cation-anion complex, [Ru2(µ-O2CC6H4-o-OMe)4(MeOH)2][Ru2Cl2(µ-O2CC6H4-o-OMe)4]. The cationic complex has two solvent molecules at the axial positions whereas the anionic complex has two chloride ligands at these positions. Complexes have been characterized by elemental analyses, mass spectrometry and IR and UV-vis-NIR spectroscopies. A magnetic study of complexes 1a, 1b, 2 and 3 have also been carried out. The crystal structure of compounds 1b and 1c have been solved by single X-ray crystal methods.

Ultrasound-assisted synthesis of water-soluble monosubstituted diruthenium compounds

The elusive monosubstituted diruthenium complexes [Ru₂Cl(DAniF)(O₂CMe)₃] (1), [Ru₂Cl(DPhF)(O₂CMe)₃] (2), [Ru₂Cl(D-p-CNPhF)(O₂CMe)₃] (3), [Ru₂Cl(D-o-TolF)(O₂CMe)₃] (4), [Ru₂Cl(D-m-TolF)(O₂CMe)₃] (5), [Ru₂Cl(D-p-TolF)(O₂CMe)₃] (6) and [Ru₂Cl(p-TolA)(O₂CMe)₃] (7) have been synthesized using for the first time ultrasound-assisted synthesis to carry out a substitution reaction in metal-metal bonded dinuclear compounds (DAniF^- = N,N'-bis(4-anisyl)formamidinate; DPhF^- = N,N'-diphenylformamidinate; D-p-CNPhF^- = N,N'-bis(4-cyanophenyl)formamidinate; D-o/m/p-TolF^- = N,N'-bis(2/3/4-tolyl)formamidinate; p-TolA^- = N-4-tolylamidate). This is a simpler and greener method than the tedious procedures described in the literature, and it has permitted to obtain water-soluble complexes with good yields in a short period of time. A synthetic study has been implemented to find the best experimental conditions to prepare compounds 1-7. Two different types of ligands, formamidinate and amidate, have been used to check the generality of the method for the preparation of monosubstituted complexes. Five new compounds (2-6) have been obtained using a formamidinate ligand, the synthesis of the previously described compound 1 has been improved, and an unprecedented monoamidate complex has been achieved (7). The crystal structures of compounds 3 and 7 have been solved by single crystal X-ray diffraction. These compounds show the typical paddlewheel structure with three acetate ligands and one formamidinate (3) or amidate (7) bridging ligand at the equatorial positions. The axial positions are occupied by the chloride ligand giving rise to one-dimensional polymer structures that were previously unknown for monosubstituted compounds.

Magnetostructural Studies on Zigzag One-Dimensional Coordination Polymers Formed by Tetraamidatodiruthenium(II,III) Paddlewheel Units Bridged by SCN Ligands

We report herein on three zigzag one-dimensional coordination polymers of {[Ru2(μ-NHOCR)4](μ-SCN)}n (R = o-Me-C6H4 (2), m-Me-C6H4 (3), p-Me-C6H4 (4)) formula. These new compounds have been obtained by reaction of the corresponding [Ru2(μ-NHOR)4(THF)2](BF4) complex with (NBu4)(SCN) under different synthetic conditions. The crystal structure of [Ru2(μ-NHOCC6H4-o-Me)4(THF)2](BF4) (1), 2 and 3 are presented. A cis-(2,2) arrangement of the amidate ligands of the [Ru2(μ-NHOCR)4]+ units is observed in all cases. Interestingly, the structures of 2 and 3 show linkage isomerism in alternated tetraamidatodiruthenium units whose axial positions are occupied by the same type of donor atom of the SCN ligands. This results in zigzag chains with a Ru-S-C angle of 98.97° and Ru-N-C angle of 169.36° in the case of 2 and 97.99° and 159.26°, respectively, in the case of 3. The magnetic data obtained for 2–4 are indicative of a σ2π4δ2(π*δ*)3 ground state (S = 3/2) and a large zero-field splitting (ZFS) in all cases (D = 54.57, 62.72 and 43.00 cm−1 for 2–4, respectively). Similar small antiferromagnetic interactions between diruthenium units (zJ = −0.93, −0.79 and −1.11 cm−1 for 2–4, respectively) are estimated for all the polymers, suggesting an analogous zigzag arrangement of the chains for 4.

Magnetic and Electrochemical Properties of Lantern-Type Dinuclear Ru(II,III) Complexes with Axial Chloride Ions or Water Molecules

By using [Ru2(O2CC3H7)4Cl]n (1) as a starting material, nBu4N[Ru2(O2CC3H7)4Cl2] (nBu4N+ = tetra(n-butyl)ammonium cation) (2) and [Ru2(O2CC3H7)4(H2O)2]BF4 (3) were prepared. The lantern-type dinuclear structures with axial chloride ions or water molecules were confirmed for 2 and 3 by X-ray crystal structure analyses. The crystal structures of 2 and 3 were compared with that of 1. In the crystal of 2, there were three crystallographically different dinuclear units; the Ru–Ru distances of each unit were 2.3094(3), 2.3046(4), and 2.3034(4) Å, respectively, which were longer than those of 1 (2.281(4) Å) and 3 (2.2584 (7) Å). Temperature dependent magnetic susceptibility measurements were performed for 1 and 2 as well as 3. The effective magnetic moments (µeff) at 300 K were 3.97 (for 1), 4.00 (for 2), and 3.97 µB (for 3), respectively. The decreases in the µeff value were confirmed for all of the complexes due to the large zero-field splitting (D): D = 68 cm−1 for 1, 78 cm−1 for 2, and 60 cm−1 for 3. Cyclic voltammograms measured in CH2Cl2 with a electrolyte of nBu4N(BF4) showed the Ru25+/Ru24+ process at −0.2–−0.4 V (vs. SCE) and the Ru26+/Ru25+ one at 1.3–1.4 V (vs. SCE), of which potentials were confirmed by the DFT calculation for nBu4N[Ru2(O2CC3H7)4Cl2].

catena-Poly[[tetrakis(μ-3,4,5-trimethoxybenzoato-κ2 O:O′)diruthenium(II,III)(Ru—Ru)]-μ-chlorido] with an unknown solvent

[Ru2Cl{μ-O2CC6H2-3,4,5-(OMe)3}4] n was prepared by the reaction of [Ru2Cl(μ-O2CCH3] n with 3,4,5-trimethoxybenzoic acid. The complex shows a paddlewheel structure with pairs of Ru atoms bridged by four carboxylate ligands. The axial positions are occupied by shared chloride ions giving zigzag chains. These chains are disposed parallel to each other to give a three-dimensional arrangement packed only by van der Waals forces. The final refinement shows high values of residual non-modelled electronic density. Therefore, the SQUEEZE utility [Spek (2015). Acta Cryst. C71, 9–18] was used to remove its contribution to the overal intensity data. The electron density modelled by SQUEEZE is consistent with around eight water molecules per unit cell.

The influence of structural isomerism on fluorescence and organic dye selective adsorption in two complexes based on flexible ligands

Based on Cd(NO₃)₂·4H₂O and 4,4'-((5-carboxy-1,3-phenylene)bis(oxy))dibenzoic acid (H₃cpbda), two isomeric coordination polymers, {[Cd_1.5(cpbda)(bpa)(H₂O)₂]·1.5H₂O}_n (1), [Cd(H₂cpbda)₂(bpa)_0.5(H₂O)]_n (2), were synthesized by using different solvent-systems. The complexes were characterized by single-crystal X-ray diffraction, IR spectroscopy, powder X-ray diffraction, and thermogravimetric analysis. Owing to the obvious structural difference between the two isomeric complexes, the further fluorescence sensing and dye selection and adsorption were investigated. The 3D tight stacking structure of 1 strengthened the fluorescence emission and the loose 2D layer structure of 2 generated the active selection and adsorption of the Malachite Green Oxalate (MGO) dye.

Anilinopyridinate-supported Ru2x+ (x = 5 or 6) paddlewheel complexes with labile axial ligands

Five new metal–metal bonded Ru₂ amidinate compounds with labile axial ligands are presented and discussed.

One-dimensional coordination polymers of [Co3(dpa)4](2+) and [MF6](2-) (M = Re(IV), Zr(IV) and Sn(IV))

One-dimensional coordination polymers of alternating metal-metal bonded trinuclear [Co3(dpa)4](2+) (dpa = the anion of 2,2'-dipyridylamine) building blocks and [ReF6](2-) (1), [ZrF6](2-) (2) or [SnF6](2-) (3) linkers have been self-assembled and crystallographically characterized. Magnetic measurements reveal a significant ferromagnetic coupling (J/k(B) = +9.9 K) between S = 1/2 {Co3(6+)} and S = 3/2 Re(IV) magnetic sites through a single, unsupported fluoride bridge in 1.