EPR Evidence for Low-Lying MLCT States in Tetracyanoiron and -ruthenium Complexes with Strongly .pi.-Accepting Chelate Ligands. Comparison with Isoelectronic Tetracarbonylmetal Species

Waldhoer, Eberhard; Poppe, Juergen; Kaim, Wolfgang; Cutin, Edgardo H.; Posse, M. E. Garcia; Katz, Néstor E.

doi:10.1021/ic00115a042

Cited by 27 publications

(13 citation statements)

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“…The isotope 99 Ru (12.7% natural abundance, I ϭ 5/2) has a 10% smaller hyperfine coupling [45] and would be still harder to detect. The maximum calculated isotropic hyperfine splitting of 0.94 mT according to Table 2 is only slightly larger than the A iso ( 101 Ru) parameters measured for radical complexes containing cyanoruthenium [37,38] (Յ0.52 mT) or other ruthenium() complex fragments (Յ0.86 mT). [39] Species with metal-centered spin containing ruthenium() [40] are expected to have isotropic metal coupling constants of several milliteslas.…”

Section: Resultsmentioning

confidence: 63%

EPR Insensitivity of the Metal‐Nitrosyl Spin‐Bearing Moiety in Complexes [L_nRu^II‐NO^·]^k

et al. 2004

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A survey of 18 paramagnetic species [L n Ru(NO)] k , including seven new examples studied by in situ electrolysis, reveals a surprisingly narrow range of EPR parameters despite a wide variety of ligands such as pyridine, polypyridines, imines, amines, nitriles, phosphanes, carbonyl, cyclopentadienides, halides, hydride, hydroxide, thiocyanate or cyanide: g 1 = 2.015 ± 0.02, g 2 = 1.990 ± 0.015, g 3 = 1.892 ± 0.03, g av = 1.968 ± 0.02, ∆g = g 1 − g 3 = 0.122 ± 0.037, A 2 ( 14 N) = 3.3 ± 0.5 mT. This rather small variability, smaller still if the organometallic compounds are excluded, differs from the wider range of EPR data reported for nitrosyliron species with S = 1/2; appar-

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Section: Resultsmentioning

confidence: 63%

EPR Insensitivity of the Metal‐Nitrosyl Spin‐Bearing Moiety in Complexes [L_nRu^II‐NO^·]^k

et al. 2004

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“…We observed hyperfine couplings (hfcs) to eight [ [41][42][43] The hfc to the imine proton (AA C H T U N G T R E N N U N G (H imine ) = 9.77 MHz) falls within the expected ranges. [44] The proton coupling constants of the pyridyl entity were revealed to be much larger compared to those of the 2,6-diisopropylphenyl substituent (between 1.14 and 1.36 MHz).…”

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confidence: 59%

Sodium and Potassium Salts of Mono‐ and Dianionic α‐Iminopyridines

Nayek

Arleth

Trapp

et al. 2011

Chemistry A European J

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[a] a-Diimine (1,4-diaza-1,3-butadiene) ligands are well established in main-group, transition-metal, and lanthanide chemistry. [1][2][3][4][5][6][7] Beside their application as ligands for latetransition-metal complexes, which can function as active and selective catalysts for a-olefin polymerization, [8] a-diimine and related ligands are of special interest due to their ability to undergo redox chemistry.[9] They have frequently been described as "non-innocent" ligands. [10][11][12] For example, in lanthanide chemistry, it has been found that the formal oxidation state of Eu [13] and Yb [14] depends on the nature of the substituents on the a-diimine ligand and on the ligand on the metal center. Thus, in both cases, the a-diimine acts either as neutral ligand or as radical anion. Reduction of adiimines, using either alkali metals or electrochemical methods, leads in each case to the corresponding radical anions [15][16][17][18] and eventually to diamagnetic dianions, [17][18][19][20][21][22][23][24] albeit at much more negative potentials. In contrast to the well-established chemistry of a-diimines, the related a-iminopyridines are much less investigated. The three different redox states of a-iminopyridines are shown in Scheme 1. The neutral system L 0 has been extensively used as ligand for late transition metals. [4,[25][26][27][28][29] Only recently, the monoanion LC À and the doubly reduced dianion L 2À were investigated as ligands in more detail. Recent reports showed a series of bis(a-iminopyridine)-metal complexes featuring aluminum [30] and the first-row transition ions (Cr, Mn, Fe, Co, Ni, and Zn) [31,32] with the monoanionic, and thus paramagnetic p-radical form of the ligand in coordination complexes. The a-iminopyridine N-2,6-diisopropylphenylimino-2-pyridine (IPy) has also been introduced in lanthanide chemistry. [33,34] In this context, a potassium derivative of the monoanionic form of a-iminopyridine was prepared in situ, but not further characterized.[34] The doubly reduced dianion has only been observed in two magnesium complexes so far. [35] In contrast, the reaction of "GaI" with a-iminopyridine leads to reductive coupling of the coordinated ligand to give neutral diamido-digallium complexes. [36] Based on this information, we were interested in a comprehensive study of the properties of the alkali metal salts of the monoanionic p-radical and the doubly reduced dianion of a-iminopyridine in solution and in the solid state. We report here the synthesis, characterization and magnetic properties of sodium and potassium salts of the mono-and dianionic a-iminopyridines.N-2,6-Diisopropylphenylimino-2-pyridine (IPy) was prepared according to literature procedures.[37] As a first entry point, we examined the electrochemical properties of IPy using cyclic voltammetry at room temperature in THF. As can be seen from Figure 1, we detected a quasi-reversible one-electron reduction process centered at E 0 1=2 = À2.57 V (vs. the ferrocene/ferrocenium couple, Fc/Fc + ), with a peakto-peak separation of 15...

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“…Increases in the solvent polarity cause blue shifts in the aborption and emission bands. The details of the interaction mechanism in the cyanide system have been described in detail by Winkler, Kaim, and Meyer . The two CN eq ligands trans to bpy show enhanced π acceptor ability in more polar environments that stabilize the Ru(II) and lower the energy of the d xz and d yz orbitals.…”

Section: Discussionmentioning

confidence: 99%

“…To date, only a few pure compounds have been reported that can optically sense water vapor concentrations in air, , so we directed our work to this area. We began with the intention to use the well-documented solvatochromic diiminetetracyanoruthenate anions − as a required structural component. The diiminetetracyanoruthenate anions are very stable and exhibit shifts in the E ° red , E ° ox , the UV−vis absorption and the emission spectra that correlate to the Gutmann acceptor number of the solvent used to dissolve the anion. , For the cation, we chose bis(triphenylphosphine)iminium (PPN + ) as it structurally resembles the “hexa-hosts” that have been investigated previously in inclusion chemistry …”

Section: Introductionmentioning

confidence: 99%

Synthesis and Spectroscopic Investigations of a Crystalline Humidity Sensor: Bis(triphenylphosphine)iminium 2,2‘-Bipyridyltetracyanoruthenate

Evju

Mann

1999

Chem. Mater.

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We have prepared a new salt of the solvatochromic [Ru(bpy)(CN)4]2- anion bis(triphenylphosphine)iminium 2,2‘-bipyridyltetracyanoruthenate, ((PPN)2[Ru(bpy)(CN)4]), that reversibly sorbs water and changes color from purple to yellow when it is exposed to humid air. Solid samples of anhydrous (PPN)2[Ru(bpy)(CN)4] reversibly hydrate in humid air, first to (PPN)2[Ru(bpy)(CN)4]·H2O and then to (PPN)2[Ru(bpy)(CN)4]·15H2O. A single-crystal X-ray study of (PPN)2[Ru(bpy)(CN)4]·2CH3CN·2(CH3CH2)2O·2H2O shows that this novel humidity sensor has large channels in the structure that allows sorbed water molecules to reversibly interact with the cyanide ligands of the chromophore. The hydration changes that result from exposure of the solid in the 0 to 66% relative humidity range cause the MLCT visible absorption bands to shift dramatically to higher energy. These hydration changes also result in large shifts in the ν(CN) region of the infrared spectrum; these changes indicate significant H-bonding interactions between sorbed water molecules and the dianionic chromophore occur in the crystal lattice. The hydration changes in the 66 to 100% relative humidity range cause large intensity changes in a visible photoluminescence band. This emission intensity increase is accompanied by small wavelength shifts in absorption and emission and in the ν(CN) region of the infrared spectrum. These changes are consistent with further oligomerization of the water molecules that initially formed hydrogen-bonding interactions to the cyanide ligands.

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EPR Evidence for Low-Lying MLCT States in Tetracyanoiron and -ruthenium Complexes with Strongly .pi.-Accepting Chelate Ligands. Comparison with Isoelectronic Tetracarbonylmetal Species

Cited by 27 publications

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EPR Insensitivity of the Metal‐Nitrosyl Spin‐Bearing Moiety in Complexes [L_nRu^II‐NO^·]^k

EPR Insensitivity of the Metal‐Nitrosyl Spin‐Bearing Moiety in Complexes [L_nRu^II‐NO^·]^k

Sodium and Potassium Salts of Mono‐ and Dianionic α‐Iminopyridines

Synthesis and Spectroscopic Investigations of a Crystalline Humidity Sensor: Bis(triphenylphosphine)iminium 2,2‘-Bipyridyltetracyanoruthenate

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EPR Evidence for Low-Lying MLCT States in Tetracyanoiron and -ruthenium Complexes with Strongly .pi.-Accepting Chelate Ligands. Comparison with Isoelectronic Tetracarbonylmetal Species

Cited by 27 publications

References 0 publications

EPR Insensitivity of the Metal‐Nitrosyl Spin‐Bearing Moiety in Complexes [LnRuII‐NO·]k

EPR Insensitivity of the Metal‐Nitrosyl Spin‐Bearing Moiety in Complexes [LnRuII‐NO·]k

Sodium and Potassium Salts of Mono‐ and Dianionic α‐Iminopyridines

Synthesis and Spectroscopic Investigations of a Crystalline Humidity Sensor: Bis(triphenylphosphine)iminium 2,2‘-Bipyridyltetracyanoruthenate

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EPR Insensitivity of the Metal‐Nitrosyl Spin‐Bearing Moiety in Complexes [L_nRu^II‐NO^·]^k

EPR Insensitivity of the Metal‐Nitrosyl Spin‐Bearing Moiety in Complexes [L_nRu^II‐NO^·]^k