Stable free radicals. X. Nitronyl nitroxide monoradicals and biradicals as possible small molecule spin labels

Ullman, Edwin F.; Osiecki, Jeanne H.; Boocock, D. G. B.; Darcy, Raphael

doi:10.1021/ja00775a031

Cited by 814 publications

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“…Simple metathesis in the presence of POMs yields the hybrid POMcontaining NN salts. In this paper, we report on the synthesis, crystal structure and magnetic properties of the Lindqvist derivative ( n Bu 3 NCH 2 NN) 2 Compound 1 crystallizes in the centrosymmetric P-1 space group [15]. The Lindqvist anions lie on a center of symmetry and are surrounded by p-MepyNN + cations that form dimeric units by π-π stacking of the pyridine fragments with an interplanar distance of ca.…”

Section: Resultsmentioning

confidence: 99%

“…Diamagnetic contributions were corrected with Pascal constants. p-MepyNNClO 4 , (TBA) 2 [W 6 O 19 ] (TBA = tetrabutylammonium) and ClCH 2 NN were prepared by previously reported procedures [13,19,20]. All other chemicals were used as received unless otherwise stated.…”

Section: Generalmentioning

confidence: 99%

“…Most of the studies have been performed with nitronyl nitroxide (NN) radicals due to their persistence, stability and ease of functionalization [2]. Bulk ferromagnetism in these compounds arises from ferromagnetic interactions between open-shell molecules in the solid state.…”

Section: Introductionmentioning

confidence: 99%

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Restricting Magnetic Interaction Pathways in Polyoxometalate Salts of Cationic Nitronyl Nitroxide Free Radicals

et al. 2004

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Section: Resultsmentioning

confidence: 99%

Section: Generalmentioning

confidence: 99%

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Restricting Magnetic Interaction Pathways in Polyoxometalate Salts of Cationic Nitronyl Nitroxide Free Radicals

et al. 2004

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“…Thenitronylnitroxide radical 2-(4-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (NITpPy)w as prepared according to [1].The Zn(NITpPy) 2 (N(CN) 2 ) 2 ) × 2NITpPy was synthesized by adding Na[N(CN) 2 ](0.045 g, 0.5 mmol) to 20 mL of an ethanol solution containing Zn(OAc) 2 × 6H 2 O(0.0112 g, 0.5m mol) and NITpPy (0.248 g, 1mmol). The mixture was stirred for 5hat room temperature and then filtered off.…”

Section: Source Of Materialsmentioning

confidence: 99%

Crystal structure of catena-bis(μ-dicyanamido)-bis[2-(4-pyridyl)- 4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide-κN)zinc(II) — 2-(4-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (1:2), Zn(C12H16N3O2)2(C2N3)2 · 2C52H64N18O8

Wang¹,

Lou²,

Hai³

2012

Zeitschrift Für Kristallographie - New Crystal Structures

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C 52 H 64 N 18 O 8 Zn, monoclinic, P2 1 /n (no. 14), a =17.825(2) Å, b =7.3268(7) Å, c =21.182(2) Å, b =92.902(1)°, V =2762.8 Å 3 , Z =2,R gt (F) =0.037, wR ref (F 2 ) =0.093, T =294 K. Source of materialThenitronylnitroxide radical 2-(4-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (NITpPy)w as prepared according to [1].The Zn(NITpPy) 2 (N(CN) 2 ) 2 ) × 2NITpPy was synthesized by adding Na[N(CN) 2 ](0.045 g, 0.5 mmol) to 20 mL of an ethanol solution containing Zn(OAc) 2 × 6H 2 O(0.0112 g, 0.5m mol) and NITpPy (0.248 g, 1mmol). The mixture was stirred for 5hat room temperature and then filtered off. Thed ark filtrate was allowedtostand at room temperature. Darkcrystals suitable for X-ray analysis were obtained after three weeks. Elemental analysis-found:C,55.10 %; H, 5.72 %; N, 22.32 %; calculated for C 52 H 64 N 18 O 8 Zn: C, 55.04 %; H, 5.69 %; N, 22.22 %. IR data areavailable in the CIF file. DiscussionAlarge number of multidimensional complexes linked by means of different bridging ligand systemssuch as azido, 4,4'-bipyridine andoxalate have markedly increased in the past fewyears [2,3]. It has also been documented that dicyanamide can be regarded as an idealligandtoconstructpolymers, due to the rich structural and topological features along with the magnetic properties related to this ligand. On the other hand, the nitronylnitroxide radicals acting as useful paramagnetic building blocks have been extensively used to assemble molecular magnetic materials [4][5][6][7]. Taking advantage of theabilitiesofbothnitroxide radicals andthe above mentioned kind of anions to coordinate transition metals, we are dealing with the use of the dicyanamide anions as bridging ligands. In the title crystal structure, the anion [N(CN) 2 ]-acts as end-toend bridging ligand giving rise to achain structure. The Zn atom is bonded to two apical NITpPy units and four equatorial N(CN) 2 units which bridge adjacent metal sites. The distorted octahedral metal site is located on an inversion center, therefore, both radicals anddicyanamide anions areintrans positions. The crystal structure consists of infinite chains of Zn(NITpPy

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“…[5] Such coalescence of the nitroxide's three hyperfine lines into a single line due to strong dipolar coupling has been observed in poly(vinyl ether) thin film with TEMPO covalently attached to the polymer side chains. [22] Also, nitroxides in some organic solvents with carbon-coordinating oxygen, such as tetrahydrofuran or ether, have shown a single line [23][24][25] EPR spectrum, where the 3 hyperfine peaks are constantly exchanged.Having identified that different nitroxide derivatives probe different local environments in Nafion, the next question is whether the local water diffusivity spatially varies with the nitroxide's location. This can be assessed by ODNP measurements.…”

mentioning

confidence: 99%

Nanometer‐Scale Water‐ and Proton‐Diffusion Heterogeneities across Water Channels in Polymer Electrolyte Membranes

Song

Han

2015

Angewandte Chemie

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Nafion, the most widely used polymer for electrolyte membranes (PEM) in fuel cells, consists of fluorocarbon backbones and acidic groups that, upon hydration, swell to form percolated channels through which water and ions diffuse. While the effects of the channel structures and the acidic groups on water/ion transport have been studied before, the surface chemistry or the spatially heterogeneous diffusivity across water channels has never been shown to directly influence water/ion transport. Using molecular spin probes that selectively partition into heterogeneous regions of PEM and Overhauser dynamic nuclear polarization relaxometry, this study reveals that both water and proton diffusivity are significantly faster near the fluorocarbon and the acidic groups lining the water channels compared to within the water channels. The concept that surface chemistry at the (sub-)nanometer scale dictates water and proton diffusivity invokes a new design principle for PEM. Keywordselectron paramagnetic resonance spectroscopy; Overhauser dynamic nuclear polarization relaxometry; water and proton dynamics; polymer electrolyte membrane; heterogeneous structure A polymer electrolyte membrane (PEM) placed between a cathode and an anode in a fuel cell, which is a device that converts chemical energy of fuel into electricity through an electrochemical reaction, should be a good conductor for protons but not for electrons and the molecular constituents of the fuel. Nafion's success as PEM stems from the good ionic conductivity through water channels, [1] as well as high chemical and mechanical stability for a wide operating temperature range between 50°C and 100°C. [2] Nafion is composed of a Correspondence to: Oc Hee Han, ohhan@kbsi.re.kr; Songi Han, songi@chem.ucsb.edu. HHS Public Access Author ManuscriptAuthor Manuscript Author ManuscriptAuthor Manuscript poly(tetrafluoroethylene) backbone with side arms decorated with sulfonic acid groups, as illustrated in Figure S1 of Supporting Information (SI). Nafion is known, upon hydration, to swell to form percolated channels through which water, protons and ions diffuse. [3] Nafion's hydrophobic domains are known to have ordered helical fibers with crystallinity similar to that of pure poly(tetrafluoroethylene) at elevated temperatures. [4] However, the exact structure and ordering of the water channels lined by the sulfonic acid groups is still a subject of controversy. Crucially, the channel dimension was found to increase linearly with the water volume fraction [3] indicating locally flat structures of the channels, [5] while scattering patterns are consistent with rod-like shapes for hydrated Nafion membrane at water volume fraction < 50%. [6][7][8] The structure and connectivity of the water channels has been thought to play an important role in the proton and water diffusivity through Nafion membranes, although a firm relationship between structure and transport function has not been established. At a hydration level of ~20 water molecules per sulfonic acid in Nafion 11...

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Stable free radicals. X. Nitronyl nitroxide monoradicals and biradicals as possible small molecule spin labels

Cited by 814 publications

References 0 publications

Restricting Magnetic Interaction Pathways in Polyoxometalate Salts of Cationic Nitronyl Nitroxide Free Radicals

Restricting Magnetic Interaction Pathways in Polyoxometalate Salts of Cationic Nitronyl Nitroxide Free Radicals

Crystal structure of catena-bis(μ-dicyanamido)-bis[2-(4-pyridyl)- 4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide-κN)zinc(II) — 2-(4-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (1:2), Zn(C12H16N3O2)2(C2N3)2 · 2C52H64N18O8

Nanometer‐Scale Water‐ and Proton‐Diffusion Heterogeneities across Water Channels in Polymer Electrolyte Membranes

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