Synthesis, Structure, and Electronic Properties of a Dimer of Ru(bpy)2 Doubly Bridged by Methoxide and Pyrazolate

Structural and electronic forms of doubly oxido/Pz and triply oxido/(Pz)2 bridged mixed valent and isovalent diruthenium complexes (Pz = pyrazolate)

The article reported on the diastereomeric dinuclear mixed-valent complexes [(acac)₂Ru(III)(μ-O)(μ-Pz^R)Ru(IV)(acac)₂] (R = H, Me, meso: ΔΛ, 1a-1c; rac: ΔΔ/ΛΛ, 2a-2c) and rac-[(acac)₂Ru(III)(μ-O)(μ-Iz)Ru(IV)(acac)₂], (2d) (HPz = pyrazole, HIz = indazole, acac = acetylacetonate). Moreover, the diruthenium(II,II) complexes [(HPz)₃Ru(II)(μ-O)(μ-Pz)₂ Ru(II)(HPz)₃] (3a) and [(HIz)₃Ru(II)(μ-O)(μ-Iz)₂Ru(II)(HIz)₃] (3d) were presented. The analogous form of 3a, i.e., [(HPz)₂(Pz)Ru(III)(μ-O)(μ-Pz)₂Ru(III)(Pz)(HPz)₂], was previously reported. Single crystal X-ray structures of 1a-1c/2a-2d and representative 3a showed their molecular forms, including the diastereomeric nature of the former. The Ru-O-Ru angle decreased appreciably on switching from doubly bridged 1 and 2 (128-135°) to triply bridged 3a (114°). Both series of complexes displayed rhombic symmetry in their EPR spectra, with g₁ and g₂ being very similar for 1a-1c with an almost axial look. The mixed-valence complex with a Ru(III)Ru(IV) (S = 1/2) state of 1 and 2 would lead to iso-valence complexes of Ru(III)Ru(III) and Ru(IV)Ru(IV) with an EPR inactive state by one electron redox reaction. On the other hand, metal based {Ru(II)Ru(II)/Ru(II)Ru(III), 3a/3a⁺} and terminal ligand (HPz/HPz^-, 3a/3a^-) based redox processes displayed anisotropic and free radical EPR, respectively. An IVCT (intervalence charge transfer) band was found for the delocalised mixed valent 1 and 2 {Ru(III)Ru(IV)} or 3a⁺ {Ru(II)Ru(III)} in the NIR region. The intense metal-to-ligand charge transfer (MLCT) transitions of 1-3 in the visible region varied systematically as a function of the metal oxidation state.

Highly Photoluminescent Blue Ionic Platinum-Based Emitters

New cycloplatinated N-heterocyclic carbene (NHC) compounds with chelate diphosphines (P^P) as ancillary ligands: [Pt(R-C^C*)(P^P)]PF₆ (R = H, P^P = dppm (1A), dppe (2A), dppbz (3A); R = CN, P^P = dppm (1B), dppe (2B), dppbz (3B)) have been prepared from the corresponding starting material [{Pt(R-C^C*)(μ-Cl)}₂] (R = H, A, R = CN, B) and fully characterized. The new compound A has been prepared by a stepwise protocol. The photophysical properties of 1A-3A and 1B-3B have been widely studied and supported by the time-dependent-density functional theory. These compounds show an efficient blue (dppe, dppbz) or cyan (dppm) emission in PMMA films (5 wt %), with photoluminescence quantum yield (PLQY) ranging from 30% to 87% under an argon atmosphere. This emission has been assigned mainly to transitions from ³ILCT [π(NHC) → π*(NHC)] excited states with some ³LL'CT [π(NHC) → π*(P^P)] character. The electroluminescence of these materials in proof-of-concept solution-processed organic light-emitting diodes containing 3A and 3B as dopants was investigated. The CIE coordinates for devices based on 3A (0.22, 0.41) and 3B (0.24, 0.44) fit within the sky blue region.

Heteroleptic Cycloplatinated N-Heterocyclic Carbene Complexes: A New Approach to Highly Efficient Blue-Light Emitters

New heteroleptic compounds of platinum(II)-containing cyclometalated N-heterocyclic carbenes, [PtCl(R-C^C*)(PPh₃)] [R-CH^C*-κC* = 3-methyl-1-(naphthalen-2-yl)-1H-imidazol-2-ylidene (R-C = Naph; 1A), 1-[4-(ethoxycarbonyl)phenyl]-3-methyl-1H-imidazol-2-ylidene (R = CO₂Et; 1B), and [Pt(R-C^C*)(py)(PPh₃)]PF₆ (py = pyridine; R-C = Naph, 2A; R = CO₂Et, 2B], have been prepared and fully characterized. All of them were obtained as the trans-(C*,PPh₃) isomer in high yields. The selectivity of their synthesis has been explained in terms of the degree of transphobia (T) of pairs of ligands in trans positions. X-ray diffraction studies on both 2A and 2B revealed that only in 2A, containing a C^C* with a more extended π system, do the molecules assemble themselves into head-to-tail pairs through intermolecular π···π contacts. The photophysical properties of 2A and 2B and those of the related compounds [Pt(NC-C^C*)(PPh₃)L]PF₆ [NC-CH^C*-κC* = 1-(4-cyanophenyl)-3-methyl-1H-imidazol-2-ylidene; L = pyridine (py; 2C), 2,6-dimethylphenylisocyanide (CNXyl; 3C), and 2-mercapto-1-methylimidazole (MMI; 4C)] have been examined to analyze the influence of the R substituent on R-C^C* (R-C = Naph; R = CO₂Et, CN) and that of the ancillary ligands (L) on them. Experimental data and time-dependent density functional theory calculations showed the similarity of the electronic features associated with R-C^C* (R = CN, CO₂Et) and their difference with respect to R-C^C* (R-C = Naph). All of the compounds are very efficient blue emitters in poly(methyl methacrylate) films under an argon atmosphere, with QY values ranging from 68% (2B) to 93% (2C). In the solid state, the color of the emission changes to yellowish-orange for compounds 2A (λ_max = 600 nm) and 3C (λ_max = 590 nm) because of the formation of aggregates through intermolecular π···π interactions. 2C and 3C were chosen to fabricate fully solution-processed electroluminescent devices with blue-light (2C), yellow-orange-light (3C), and white-light (mixtures of 2C and 3C) emission from neat films of the compounds as emitting layers.

Competitive coordination aggregation for V-shaped [Co3] and disc-like [Co7] complexes: synthesis, magnetic properties and catechol oxidase activity

The synthetic procedures, magnetic properties and catecholase-like activity of a V-shaped [CoII3L₄] and planar disc-like [CoII7L₆] complexes have been discussed.

(2,2'-Bi-pyridine)-chlorido-[diethyl (2,2':6',2''-terpyridin-4-yl)phospho-nate]ruthenium(II) hexa-fluorido-phosphate aceto-nitrile/water solvate

The cationic complex in the title compound, [RuCl(C₁₀H₈N₂)(C₁₉H₂₀N₃O₃P)]PF₆·0.83CH₃CN·0.17H₂O, is a water-oxidation precatalyst functionalized for TiO₂ attachment via terpyridine phospho­nate. The The Ru^II atom in the complex has a distorted octa­hedral geometry due to the restricted bite angle [159.50 (18)°] of the terpyridyl ligand. The dihedral angle between the least-squares planes of the terpyridyl and bipyridyl moieties is 86.04 (14)°. The mean Ru—N bond length for bi­pyridine is 2.064 (5) Å, with the bond opposite to Ru—Cl being 0.068 Å shorter. For the substituted terpyridine, the mean Ru—N distance involving the outer N atoms trans to each other is 2.057 (6) Å, whereas the bond length involving the central N atom is 1.944 (5) Å. The Ru—Cl distance is 2.4073 (15) Å. The P atom of the phospho­nate group lies in the same plane as its adjacent pyridyl ring, with the ordinary character of the bond between P and C_tpy [1.801 (6) Å] allowing for free rotation of the terpyridine substituent around the P—C_tpy axis. The aceto­nitrile solvent mol­ecule was refined to be disordered with two water mol­ecules; occupancies for the acetontrile and water mol­ecules were 0.831 (9) and 0.169 (9), respectively. Also disordered was the PF₆⁻ counter-ion (over three positions) and one of the eth­oxy substituents (with two positions). The crystal structure shows significant intra- and inter­molecular H⋯X contacts, especially some involving the Cl⁻ ligand.

trans-Diaqua-bis(2,2'-bipyridine-κN,N')ruthenium(II) bis-(trifluoro-methane-sulfonate)

The title compound, trans-[Ru(bpy)₂(H₂O)₂](CF₃SO₃)₂ (bpy = 2,2′-bipyridine, C₁₀H₈N₂), crystallized from the decomposition of an aged aqueous solution of a dimeric complex of cis-Ru(bpy)₂ in 0.1 M triflic acid. The Ru^II ion is located on a crystallographic inversion center and exhibits a distorted octa­hedral coordination with equivalent ligands trans to each other. The Ru—O distance is 2.1053 (16) Å and the Ru—N distances are 2.0727 (17) and 2.0739 (17) Å. The bpy ligands are bent, due to inter-ligand steric inter­actions between H atoms of opposite pyridyl units across the Ru center. The crystal structure exhibits an extensive hydrogen-bonding network involving the water ligands and the trifluoromethane­sulfonate counter-ions within two-dimensional layers, although no close hydrogen-bond inter­actions exist between different layers.