Intramolecular Exchange Coupling Research Articles

Magnetic properties of new Fe 6(triethanolaminate(3-)) 6 spin-clusters

We report the magnetic properties of three cyclic hexanuclear iron(III) spin-clusters ([Fe 6(tea) 6] · 6MeOH ( 1), [NaFe 6(tea) 6]ClO 4 · 2MeOH ( 2) and [LiFe 6(tea) 6]ClO 4 · 2MeOH ( 3), (tea: triethanolaminate(3-)). The intra-molecular exchange coupling between the Fe III-spins is determined by measurements of the magnetic susceptibility in the range 2–300 K. The zero-field splitting of the lowest cluster spin states ( E/k B < 200K) is studied by ESR (electron-spin resonance) at frequencies between 9.5 and 350 GHz. The level splitting is analyzed by the irreducible-tensor operator technique.

Intramolecular Long Range Electronic Spin Exchange Coupling in Diradicals: A New Magnetic Coupling Unit

Abstract A phenyl diethynyl bridge is used as a magnetic coupling unit (MCU) between two iminonitroxide π-radicals. The ethynyl moiety is attached to the central phenyl ring either in the para or in the meta position. The magnetic properties of the resulting bis-imino nitroxide diradicals (p-BIN and m-BIN) are investigated both at the molecular scale and in the condensed phases. An intramolecular through bond spin coupling is observed at an unusual long distance (about 20 ÅS) in both derivatives. However, the ground state is found to be a singlet spin state in both compounds. The results suggest an interplay between the spin polarization and the spin delocalization (π-conjugation). An intermolecular weak antiferromagnetic spin coupling is occuring in both compounds.

Intramolecular exchange coupling of arylnitrenes by OXYGEN

AbstractA series of m,n′‐diazidodiphenyl ethers (m ≤ n, m = 3,4; n = 3,4) was photolyzed at 77 K in frozen, glassy 2‐methyltetrahydrofuran matrices to generate the corresponding diphenyl ether m,n′‐dinitrenes for study by electron spin resonance (ESR) spectroscopy. 3,4′‐Diazidodiphenyl ether gave an ESR spectrum dominated by a mononitrene peak with ∣D/hc∣ = 0·972 cm−1, and also showed a weak dinitrene quintet spectrum with ∣D/hc∣ = 0·162 cm−1 having ESR spectral intensity vs temperature dependence (Curie law) consistent with either a high‐spin ground state or a very small singlet–quintet gap. Di(3‐azidophenyl) ether gave a strong mononitrene peak with ∣D/hc∣ = 0·996 cm−1 and a quintet dinitrene ESR spectrum (∣D/hc∣ = 0·162 cm−1) which exhibited non‐linear Curie law intensity behavior consistent with the quintet being a thermally populated excited state 40 cal mol−1 above a singlet ground state. Di(4‐azidophenyl) ether gave a strong mononitrene peak with ∣D/hc∣ = 0·961 cm−1, but no observable spectrum related to a high‐spin open‐shell dinitrene. The results are consistent with oxygen being a weak exchange coupling linker in pi‐conjugated open‐shell molecules. The observed ground‐state spin multiplicities are in accord with qualitative superexchange and connectivity models, despite any perturbations due to resonance effects between the oxygen linker and p‐nitrene sites.

ChemInform Abstract: Persistent 1,3,5‐Benzenetriyltris(N‐tert‐butyl nitroxide) and Its Analogues with Quartet Ground States. Intramolecular Triangular Exchange Coupling Among Three Nitroxide Radical Centers

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Persistent 1,3,5-benzenetriyltris(N-tert-butyl nitroxide) and its analogs with quartet ground states. Intramolecular triangular exchange coupling among three nitroxide radical centers

1,3,5-Benzenetriyltris(N-tert-butyl nitroxide (3), its 2-methoxy derivative (4), and 1,3,5-tris{p-(N-oxy-N-tert-butylamino)phenyl}benzene (5) were prepared and studied by EPR and magnetic susceptibility/magnetization measurements. Trinitroxides 3 and 4 showed EPR fine structures characteristic of quartet states: 3: g=2,0062, |D/hc|=0.009 32 cm -1 and |E/hc|=0.000 15 cm -1 ; 4: g=2.0063, |D/hc|=0.009 66 cm -1 and |E/hc|=0.000 32 cm -1 . The changes in the signal intensity vs reciprocal temperature obeyed Curie's law in the range 10-100 K, suggesting that the quartets are their ground states. Magnetization data for 3 and 4 at 1.8, 3.0, and 4.0 K in the field range 0-7 T obeyed the Brillouin function in which S=3/2

Models for intramolecular exchange in organic .pi.-conjugated open-shell systems: a comparison of three non-Kekule biphenyldinitrenes

The important effect of connectivity upon the nature of intramolecular exchange coupling of unpaired electrons by the biphenyl group was investigated by cryogenic matrix photolysis of diazide precursors expected to yield biphenyl-3,4'-dinitrene (1), biphenyl-3,3'-dinitrene (2), and biphenyl-4,4'-dinitrene (3). System 1 was predicted by parity-based qualitative models to exhibit a high-spin ground state. By Curie law analysis of its electron spin resonance (SSR) spectrum at cryogenic temperatures in frozen 2-methyltetrahydrofuran solution, 1 was found to be a quintet ground-state dinitrene with zero field splitting (zfs) parameters of |D/hc|=0.153 cm -1 , |E/hc|=0.003 cm -1

ChemInform Abstract: Magnetic Properties and EPR Spectra of Tetranuclear Copper(II) Complexes.

AbstractAnalysis of the low‐temp.

1,4,7-Triazacyclononane and N,N'N''-trimethyl-1,4,7-triazacyclononane - two versatile macrocycles for the synthesis of monomeric and oligomeric metal complexes

Abstract

Magnetic properties and EPR spectra of tetranuclear copper(II) complexes

The low-temperature EPR powder spectra of four tetrameric oxygen-bridged copper(II) complexes with ligands, (L), derived from pyridoxal and amino- alcohols, (Cu 4L 4)· xCH 3OH, are reported. A comparison of the electron paramagnetic resonance study with the magnetic susceptibility measurements provides further informations on the magnetic properties of these compounds. The ferromagnetic nature of the resulting intramolecular exchange coupling into the Cu 4O 4 core is observed for the four complexes. For one peculiar tetramer the evolution of the EPR spectra by gradual loss of the solvent is presented, to show the importance of the solvent molecules and of the resulting hydrogen bond network to maintain the tetrameric structure.