Ruthenium, Rhodium, Osmium, and Iridium Complexes of Osazones (Osazones = Bis-Arylhydrazones of Glyoxal): Radical versus Nonradical States

Phenyl osazone (L^NHPhH₂), phenyl osazone anion radical (L^NHPhH₂^•–), benzoyl osazone (L^NHCOPhH₂), benzoyl osazone anion radical (L^NHCOPhH₂^•–), benzoyl osazone monoanion (L^NCOPhHMe^–), and anilido osazone (L^NHCONHPhHMe) complexes of ruthenium, osmium, rhodium, and iridium of the types <i>trans</i>-[Os­(L^NHPhH₂)­(PPh₃)₂Br₂] (<b>3</b>), <i>trans</i>-[Ir­(L^NHPhH₂^•–)­(PPh₃)₂Cl₂] (<b>4</b>), <i>trans</i>-[Ru­(L^NHCOPhH₂)­(PPh₃)₂Cl₂] (<b>5</b>), <i>trans</i>-[Os­(L^NHCOPhH₂)­(PPh₃)₂Br₂] (<b>6</b>), <i>trans</i>- [Rh­(L^NHCOPhH₂^•–)­(PPh₃)₂Cl₂] (<b>7</b>), <i>trans</i>-[Rh­(L^NHCOPhHMe^–)­(PPh₃)₂Cl]­PF₆ ([<b>8</b>]­PF₆), and <i>trans</i>-[Ru­(L^NHCONHPhHMe)­(PPh₃)₂Cl]Cl ([<b>9</b>]­Cl) have been isolated and compared (osazones = bis-arylhydrazones of glyoxal). The complexes have been characterized by elemental analyses and IR, mass, and ¹H NMR spectra; in addition, single-crystal X-ray structure determinations of <b>5</b>, <b>6</b>, [<b>8</b>]­PF₆, and [<b>9</b>]Cl have been carried out. EPR spectra of <b>4</b> and <b>7</b> reveal that in the solid state they are osazone anion radical complexes (<b>4</b>, <i>g</i>_av = 1.989; <b>7</b>, 2.028 (Δ<i>g</i> = 0.103)), while in solution the contribution of the M­(II) ions is greater (<b>4</b>, <i>g</i>_av = 2.052 (Δ<i>g</i> = 0.189); <b>7</b>, <i>g</i>_av = 2.102 (Δ<i>g</i> = 0.238)). Mulliken spin densities on L^NHPhH₂ and L^NHCOPhH₂ obtained from unrestricted density functional theory (DFT) calculations on <i>trans</i>-[Ir­(L^NHPhH₂)­(PMe₃)₂Cl₂] (<b>4</b>^Me) and <i>trans</i>-[Rh­(L^NHCOPhH₂)­(PMe₃)₂Cl₂] (<b>7</b>^Me) in the gas phase with doublet spin states authenticated the existence of L^NHPhH₂^•– and L^NHCOPhH₂^•– anion radicals in <b>4</b> and <b>7</b> coordinated to iridium­(III) and rhodium­(III) ions. DFT calculations on <i>trans</i>-[Os­(L^NHPhH₂)­(PMe₃)₂Br₂] (<b>3</b>^Me), <i>trans</i>-[Os­(L^NHCOPhH₂)­(PMe₃)₂Br₂] (<b>6</b>^Me), and <i>trans</i>-[Ru­(L^NHCONHPhHMe^–)­(PMe₃)₂Cl] [<b>9</b>^Me]⁺ with singlet spin states established that the closed-shell singlet state (CSS) solutions of <b>3</b>, <b>5</b>, <b>6</b>, and [<b>9</b>]­Cl are stable. The lower value of M^III/M^II reduction potentials and lower energy absorption bands corroborate the higher extent of mixing of d orbitals with the π* orbital in the case of <b>3</b> and <b>6</b>. Time-dependent (TD) DFT calculations elucidated the MLCT as the origin of the lower energy absorption bands of <b>3</b>, <b>5</b>, and <b>6</b> and π → π* as the origin of transitions in <b>4</b> and <b>7</b>

Ruthenium, Rhodium, Osmium, and Iridium Complexes of Osazones (Osazones = Bis-Arylhydrazones of Glyoxal): Radical versus Nonradical States

Phenyl osazone (L^NHPhH₂), phenyl osazone anion radical (L^NHPhH₂^•–), benzoyl osazone (L^NHCOPhH₂), benzoyl osazone anion radical (L^NHCOPhH₂^•–), benzoyl osazone monoanion (L^NCOPhHMe^–), and anilido osazone (L^NHCONHPhHMe) complexes of ruthenium, osmium, rhodium, and iridium of the types <i>trans</i>-[Os­(L^NHPhH₂)­(PPh₃)₂Br₂] (<b>3</b>), <i>trans</i>-[Ir­(L^NHPhH₂^•–)­(PPh₃)₂Cl₂] (<b>4</b>), <i>trans</i>-[Ru­(L^NHCOPhH₂)­(PPh₃)₂Cl₂] (<b>5</b>), <i>trans</i>-[Os­(L^NHCOPhH₂)­(PPh₃)₂Br₂] (<b>6</b>), <i>trans</i>- [Rh­(L^NHCOPhH₂^•–)­(PPh₃)₂Cl₂] (<b>7</b>), <i>trans</i>-[Rh­(L^NHCOPhHMe^–)­(PPh₃)₂Cl]­PF₆ ([<b>8</b>]­PF₆), and <i>trans</i>-[Ru­(L^NHCONHPhHMe)­(PPh₃)₂Cl]Cl ([<b>9</b>]­Cl) have been isolated and compared (osazones = bis-arylhydrazones of glyoxal). The complexes have been characterized by elemental analyses and IR, mass, and ¹H NMR spectra; in addition, single-crystal X-ray structure determinations of <b>5</b>, <b>6</b>, [<b>8</b>]­PF₆, and [<b>9</b>]Cl have been carried out. EPR spectra of <b>4</b> and <b>7</b> reveal that in the solid state they are osazone anion radical complexes (<b>4</b>, <i>g</i>_av = 1.989; <b>7</b>, 2.028 (Δ<i>g</i> = 0.103)), while in solution the contribution of the M­(II) ions is greater (<b>4</b>, <i>g</i>_av = 2.052 (Δ<i>g</i> = 0.189); <b>7</b>, <i>g</i>_av = 2.102 (Δ<i>g</i> = 0.238)). Mulliken spin densities on L^NHPhH₂ and L^NHCOPhH₂ obtained from unrestricted density functional theory (DFT) calculations on <i>trans</i>-[Ir­(L^NHPhH₂)­(PMe₃)₂Cl₂] (<b>4</b>^Me) and <i>trans</i>-[Rh­(L^NHCOPhH₂)­(PMe₃)₂Cl₂] (<b>7</b>^Me) in the gas phase with doublet spin states authenticated the existence of L^NHPhH₂^•– and L^NHCOPhH₂^•– anion radicals in <b>4</b> and <b>7</b> coordinated to iridium­(III) and rhodium­(III) ions. DFT calculations on <i>trans</i>-[Os­(L^NHPhH₂)­(PMe₃)₂Br₂] (<b>3</b>^Me), <i>trans</i>-[Os­(L^NHCOPhH₂)­(PMe₃)₂Br₂] (<b>6</b>^Me), and <i>trans</i>-[Ru­(L^NHCONHPhHMe^–)­(PMe₃)₂Cl] [<b>9</b>^Me]⁺ with singlet spin states established that the closed-shell singlet state (CSS) solutions of <b>3</b>, <b>5</b>, <b>6</b>, and [<b>9</b>]­Cl are stable. The lower value of M^III/M^II reduction potentials and lower energy absorption bands corroborate the higher extent of mixing of d orbitals with the π* orbital in the case of <b>3</b> and <b>6</b>. Time-dependent (TD) DFT calculations elucidated the MLCT as the origin of the lower energy absorption bands of <b>3</b>, <b>5</b>, and <b>6</b> and π → π* as the origin of transitions in <b>4</b> and <b>7</b>

Polypropylene and Graphene Nanocomposites: Effects of Selected 2D-Nanofiller’s Plate Sizes on Fundamental Physicochemical Properties

The authors developed a nanocomposite using polypropylene (PP) and graphene nanoplatelets (GNPs) with a melt mixing method. Virgin PP was filled with three sets of GNPs with a fixed thickness (15 nm) and surface area (50–80 m2/g). The selected H-type GNPs had three different sizes of 5, 15 and 25 µm. The nanocomposites were made by loading GNPs at 1, 2 and 3 wt.%. Mechanical analysis was carried out by performing tensile, flexural and impact strength tests. The crystalline, micro-structural, thermal and dynamic mechanical properties were assessed through XRD, FESEM, PLM, DSC, TGA and DMA tests. It was observed that all three types of GNPs boosted the mechanical strength of the polymer composite. Increasing the nanofiller size decreased the tensile strength and the tensile modulus, increased the flexural strength and flexural modulus, and increased the impact strength. Maximum tensile strength (≈41.18 MPa) resulted for the composite consisting 3 wt.% H5, whereas maximum flexural (≈50.931 MPa) and impact (≈42.88 J/m) strengths were observed for nanocomposite holding 3 wt.% H25. Graphene induced the PP’s crystalline phases and structure. An improvement in thermal stability was seen based on the results of onset degradation (TD) and melting (Tm) temperatures. Graphene increased the crystallization (Tc) temperatures, and acted like a nucleating agent. The experimental analysis indicated that the lateral size of graphene plays an important role for the nanocomposite’s homogeneity. It was noted that the small-sized GNPs improved dispersion and decreased agglomeration. Thus overall, small-sized GNPs are preferable, and increasing the lateral size hardly establishes feasible characteristics in the nanocomposite

Ambient-Stable Bis-Azoaromatic-Centered Diradical (L-center dot)M(L-center dot)] Complexes of Rh(III): Synthesis, Structure, Redox, and Spin-Spin Interaction

Bis-azoaromatic electron traps, viz. 2-(2-pyridylazo)azoarene 1, have been synthesized by colligating electron-deficient pyridine and azoarene moieties, and they act as apposite proradical templates for the formation of stable open-shell diradical complexes (1(center dot-))Rh-III(1(center dot-))](+) (2](+)), starting from the low-valent electron reservoir Rh-I]. The less stable monoradical Rh-III(1(center dot-))Cl-2(PPh3)(3)] (3) has also been isolated as a minor product. These p-radical complexes are multiredox systems, and the electron transfer processes occur exclusively within the pincer-type NNN ligand backbone 1. Molecular and electronic structures of the diradicals and monoradicals have been ascertained with the aid of X-ray diffraction, electrochemical, spectroelectrochemical, and spectral (electronic, IR, NMR, and EPR) studies. In the diradicals 2](+), the orthogonal disposition of two ligand pi orbitals linked via a closed-shell metal center (t(2)(6)) impedes significant coupling between the radicals. Indeed, the observed magnetic moment of 2a](+) lies near similar to 2.3 mu(B) over the temperature range 50-300 K. A very weak antiferromagnetic (AF) intramolecular spin-spin interaction between two ligand pi arrays in (1(center dot-))Rh-III(1(center dot-))](+) have been found experimentally (J approximate to -5 cm(-1)), and this is further substantiated by density functional theory (DFT) calculations at the (U)B3LYP/6-31G(d,p) level

Ambient-Stable Bis-Azoaromatic-Centered Diradical [(L^•)M(L^•)] Complexes of Rh(III): Synthesis, Structure, Redox, and Spin–Spin Interaction

Bis-azoaromatic electron traps, viz. 2-(2-pyridylazo)­azoarene <b>1</b>, have been synthesized by colligating electron-deficient pyridine and azoarene moieties, and they act as apposite proradical templates for the formation of stable open-shell diradical complexes [(<b>1</b>^•–)­Rh^III(<b>1</b>^•–)]⁺ ([<b>2</b>]⁺), starting from the low-valent electron reservoir [Rh^I]. The less stable monoradical [Rh^III(<b>1</b>^•–)­Cl₂(PPh₃)₃] (<b>3</b>) has also been isolated as a minor product. These π-radical complexes are multiredox systems, and the electron transfer processes occur exclusively within the pincer-type NNN ligand backbone <b>1</b>. Molecular and electronic structures of the diradicals and monoradicals have been ascertained with the aid of X-ray diffraction, electrochemical, spectroelectrochemical, and spectral (electronic, IR, NMR, and EPR) studies. In the diradicals [<b>2</b>]⁺, the orthogonal disposition of two ligand π orbitals linked via a closed-shell metal center (t₂⁶) impedes significant coupling between the radicals. Indeed, the observed magnetic moment of [<b>2a</b>]^<b>+</b> lies near ∼2.3 μ_B over the temperature range 50–300 K. A very weak antiferromagnetic (AF) intramolecular spin–spin interaction between two ligand π arrays in [<b>(1</b>^•–)­Rh^III(<b>1</b>^•–)]⁺ have been found experimentally (<i>J</i> ≈ −5 cm^–1), and this is further substantiated by density functional theory (DFT) calculations at the (U)­B3LYP/6-31G­(d,p) level

Electronic Structures of Ruthenium and Osmium Complexes of 9,10-Phenanthrenequinone

The reaction of 9,10-phenanthrenequinone (PQ) with [M^II(H)­(CO)­(X)­(PPh₃)₃] in boiling toluene leads to the homolytic cleavage of the M^II–H bond, affording the paramagnetic <i>trans</i>-[M­(PQ)­(PPh₃)₂(CO)­X] (M = Ru, X = Cl, <b>1</b>; M = Os, X = Br, <b>3</b>) and <i>cis</i>-[M­(PQ)­(PPh₃)₂(CO)­X] (M = Ru, X = Cl, <b>2</b>; M = Os, X = Br, <b>4</b>) complexes. Single-crystal X-ray structure determinations of <b>1</b>, <b>2</b>·toluene, and <b>4·</b>CH₂Cl₂, EPR spectra, and density functional theory (DFT) calculations have substantiated that <b>1</b>–<b>4</b> are 9,10-phenanthrenesemiquinone radical (PQ^•–) complexes of ruthenium­(II) and osmium­(II) and are defined as <i>trans</i>-[Ru^II(PQ^•–)­(PPh₃)₂(CO)­Cl] (<b>1</b>), <i>cis</i>-[Ru^II(PQ^•–)­(PPh₃)₂(CO)­Cl] (<b>2</b>), <i>trans</i>-[Os^II(PQ^•–)­(PPh₃)₂(CO) Br] (<b>3</b>), and <i>cis</i>-[Os^II(PQ^•–)­(PPh₃)₂(CO)­Br] (<b>4</b>). Two comparatively longer C–O [average lengths: <b>1</b>, 1.291(3) Å; <b>2</b>·toluene, 1.281(5) Å; <b>4</b>·CH₂Cl₂, 1.300(8) Å] and shorter C–C lengths [<b>1</b>, 1.418(5) Å; <b>2</b>·toluene, 1.439(6) Å; <b>4</b>·CH₂Cl₂, 1.434(9) Å] of the OO chelates are consistent with the presence of a reduced PQ^•– ligand in <b>1</b>–<b>4</b>. A minor contribution of the alternate resonance form, <i>trans</i>- or <i>cis</i>-[M^I(PQ)­(PPh₃)₂(CO)­X], of <b>1</b>–<b>4</b> has been predicted by the anisotropic X- and Q-band electron paramagnetic resonance spectra of the frozen glasses of the complexes at 25 K and unrestricted DFT calculations on <b>1</b>, <i>trans</i>-[Ru­(PQ)­(PMe₃)₂(CO)­Cl] (<b>5</b>), <i>cis</i>-[Ru­(PQ)­(PMe₃)₂(CO)­Cl] (<b>6</b>), and <i>cis</i>-[Os­(PQ)­(PMe₃)₂(CO)­Br] (<b>7</b>). However, no thermodynamic equilibria between [M^II(PQ^•–)­(PPh₃)₂(CO)­X] and [M^I(PQ)­(PPh₃)₂(CO)­X] tautomers have been detected. <b>1</b>–<b>4</b> undergo one-electron oxidation at −0.06, −0.05, 0.03, and −0.03 V versus a ferrocenium/ferrocene, Fc⁺/Fc, couple because of the formation of PQ complexes as <i>trans</i>-[Ru^II(PQ)­(PPh₃)₂(CO)­Cl]⁺ (<b>1</b>^<b>+</b>), <i>cis</i>-[Ru^II(PQ)­(PPh₃)₂(CO)­Cl]⁺ (<b>2</b>^<b>+</b>), <i>trans</i>-[Os^II(PQ)­(PPh₃)₂(CO)­Br]⁺ (<b>3</b>^<b>+</b>), and <i>cis</i>-[Os^II(PQ)­(PPh₃)₂(CO)­Br]⁺ (<b>4</b>^<b>+</b>). The trans isomers <b>1</b> and <b>3</b> also undergo one-electron reduction at −1.11 and −0.96 V, forming PQ^2– complexes <i>trans</i>-[Ru^II(PQ^2–)­(PPh₃)₂(CO)­Cl]⁻ (<b>1</b>^<b>–</b>) and <i>trans</i>-[Os^II(PQ^2–)­(PPh₃)₂(CO)­Br]⁻ (<b>3</b>^<b>–</b>). Oxidation of <b>1</b> by I₂ affords diamagnetic <b>1</b>^<b>+</b>I₃^– in low yields. Bond parameters of <b>1</b>^<b>+</b>I₃^– [C–O, 1.256(3) and 1.258(3) Å; C–C, 1.482(3) Å] are consistent with ligand oxidation, yielding a coordinated PQ ligand. Origins of UV–vis/near-IR absorption features of <b>1</b>–<b>4</b> and the electrogenerated species have been investigated by spectroelectrochemical measurements and time-dependent DFT calculations on <b>5</b>, <b>6</b>, <b>5</b>^<b>+</b>, and <b>5</b>^<b>–</b>

Electronic Structures of Ruthenium and Osmium Complexes of 9,10-Phenanthrenequinone

The reaction of 9,10-phenanthrenequinone (PQ) with [M^II(H)­(CO)­(X)­(PPh₃)₃] in boiling toluene leads to the homolytic cleavage of the M^II–H bond, affording the paramagnetic <i>trans</i>-[M­(PQ)­(PPh₃)₂(CO)­X] (M = Ru, X = Cl, <b>1</b>; M = Os, X = Br, <b>3</b>) and <i>cis</i>-[M­(PQ)­(PPh₃)₂(CO)­X] (M = Ru, X = Cl, <b>2</b>; M = Os, X = Br, <b>4</b>) complexes. Single-crystal X-ray structure determinations of <b>1</b>, <b>2</b>·toluene, and <b>4·</b>CH₂Cl₂, EPR spectra, and density functional theory (DFT) calculations have substantiated that <b>1</b>–<b>4</b> are 9,10-phenanthrenesemiquinone radical (PQ^•–) complexes of ruthenium­(II) and osmium­(II) and are defined as <i>trans</i>-[Ru^II(PQ^•–)­(PPh₃)₂(CO)­Cl] (<b>1</b>), <i>cis</i>-[Ru^II(PQ^•–)­(PPh₃)₂(CO)­Cl] (<b>2</b>), <i>trans</i>-[Os^II(PQ^•–)­(PPh₃)₂(CO) Br] (<b>3</b>), and <i>cis</i>-[Os^II(PQ^•–)­(PPh₃)₂(CO)­Br] (<b>4</b>). Two comparatively longer C–O [average lengths: <b>1</b>, 1.291(3) Å; <b>2</b>·toluene, 1.281(5) Å; <b>4</b>·CH₂Cl₂, 1.300(8) Å] and shorter C–C lengths [<b>1</b>, 1.418(5) Å; <b>2</b>·toluene, 1.439(6) Å; <b>4</b>·CH₂Cl₂, 1.434(9) Å] of the OO chelates are consistent with the presence of a reduced PQ^•– ligand in <b>1</b>–<b>4</b>. A minor contribution of the alternate resonance form, <i>trans</i>- or <i>cis</i>-[M^I(PQ)­(PPh₃)₂(CO)­X], of <b>1</b>–<b>4</b> has been predicted by the anisotropic X- and Q-band electron paramagnetic resonance spectra of the frozen glasses of the complexes at 25 K and unrestricted DFT calculations on <b>1</b>, <i>trans</i>-[Ru­(PQ)­(PMe₃)₂(CO)­Cl] (<b>5</b>), <i>cis</i>-[Ru­(PQ)­(PMe₃)₂(CO)­Cl] (<b>6</b>), and <i>cis</i>-[Os­(PQ)­(PMe₃)₂(CO)­Br] (<b>7</b>). However, no thermodynamic equilibria between [M^II(PQ^•–)­(PPh₃)₂(CO)­X] and [M^I(PQ)­(PPh₃)₂(CO)­X] tautomers have been detected. <b>1</b>–<b>4</b> undergo one-electron oxidation at −0.06, −0.05, 0.03, and −0.03 V versus a ferrocenium/ferrocene, Fc⁺/Fc, couple because of the formation of PQ complexes as <i>trans</i>-[Ru^II(PQ)­(PPh₃)₂(CO)­Cl]⁺ (<b>1</b>^<b>+</b>), <i>cis</i>-[Ru^II(PQ)­(PPh₃)₂(CO)­Cl]⁺ (<b>2</b>^<b>+</b>), <i>trans</i>-[Os^II(PQ)­(PPh₃)₂(CO)­Br]⁺ (<b>3</b>^<b>+</b>), and <i>cis</i>-[Os^II(PQ)­(PPh₃)₂(CO)­Br]⁺ (<b>4</b>^<b>+</b>). The trans isomers <b>1</b> and <b>3</b> also undergo one-electron reduction at −1.11 and −0.96 V, forming PQ^2– complexes <i>trans</i>-[Ru^II(PQ^2–)­(PPh₃)₂(CO)­Cl]⁻ (<b>1</b>^<b>–</b>) and <i>trans</i>-[Os^II(PQ^2–)­(PPh₃)₂(CO)­Br]⁻ (<b>3</b>^<b>–</b>). Oxidation of <b>1</b> by I₂ affords diamagnetic <b>1</b>^<b>+</b>I₃^– in low yields. Bond parameters of <b>1</b>^<b>+</b>I₃^– [C–O, 1.256(3) and 1.258(3) Å; C–C, 1.482(3) Å] are consistent with ligand oxidation, yielding a coordinated PQ ligand. Origins of UV–vis/near-IR absorption features of <b>1</b>–<b>4</b> and the electrogenerated species have been investigated by spectroelectrochemical measurements and time-dependent DFT calculations on <b>5</b>, <b>6</b>, <b>5</b>^<b>+</b>, and <b>5</b>^<b>–</b>