Nitroxide-substituted nitronyl nitroxide and iminonitroxide.

We report on the highly compact nitroxide-substituted nitronyl nitroxide 1 and iminonitroxide 2; they have isoelectronic structures with trimethylenemethane. These diradicals are stable under aerated conditions at room temperature and have large positive exchange interactions: J/k(B) = +390 K (H = -2JS(1)(/)(2)·S(1/2)) for 1 and J/k(B) ≈ +550 K for 2.

A new ferrimagnet based on a radical-substituted radical cation salt.

Radical-substituted radical cations are attractive spin building blocks of molecule-based magnets. The introduction of an additional spin as a counteranion provides a unique three-spin system wherein the magnetic interactions between the spins of the radical substituent and the radical cation (J(intra)) and those between the spins of the radical cation and the anion (J(inter)) play decisive roles in determining the magnetic properties of the system. We report the first demonstration of a ferrimagnet by utilizing a large-J(intra) system, nitronyl nitroxide-substituted dihydrophenazine radical cation (NNDPP(*+)) in combination with tetrabromoferrate (FeBr(4)(-)) as the counteranion. On the basis of measurements of dc and ac magnetic susceptibilities and heat capacity, the magnetic properties of NNDPP(*+) x FeBr(4)(-) are elucidated to be those of a three-dimensional long-range-ordered ferrimagnet with T(c) = 6.7 K.

Preparation, structure, and magnetic interaction of a Mn(hfac)2-bridged [2-(3-pyridyl)(nitronyl nitroxide)-Mn(hfac)2]2 chain complex.

A new one-dimensional chain complex, Mn(hfac)(2)-bridged [2-(3-pyridyl)(nitronyl nitroxide)Mn(hfac)(2)](2), was prepared and its structure and magnetic properties were elucidated; the complex exhibited a large antiferromagnetic interaction of J(1)=-185 K between the three Mn(ii) atoms and the two nitronyl nitroxides to give S=13/2 spin units and a small ferromagnetic interaction of J(3)'=+0.02 K between these spin units at low temperatures (50-1.9 K), compatible with the theoretical analysis for model compounds.

Remarkable structure deformation in phenothiazine trimer radical cation.

[structure: see text] A trimeric phenothiazine and its radical cation were prepared, and their structures were elucidated. In contrast to a largely twisted structure in the neutral species, the radical cation had a unique structure deformation that allowed charge-transfer-type conjugation from the outer phenothiazine rings to the central phenothiazine radical cation.

(Nitronyl nitroxide)-substituted trioxytriphenylamine radical cation tetrachlorogallate salt: a 2p-electron-based weak ferromagnet composed of a triplet diradical cation.

The synthesis and the solid state magnetic properties of (nitronyl nitroxide)-substituted trioxytriphenylamine radical cation tetrachlorogallate, NNTOT(+)⋅GaCl(4)(-), are reported. In the temperature region between 300 and 3 K, the magnetic behavior is characterized by the strong intramolecular ferromagnetic interaction (J/k(B)=+400 K) between the radical (NN) and the radical cation (TOT(+)) and the weak intermolecular antiferromagnetic interaction (J/k(B)=-1.9 K) between NNTOT(+) ions. Below 3 K, a 3D-type long-range magnetic ordering into a weak ferromagnet was observed (T(N)=2.65 K). The magnetic entropy (S(mag)=8.97 J K(-1) mol(-1)) obtained by the heat capacity measurement is in good agreement with the theoretical value of R ln3=9.13 J K(-1) mol(-1) based on the S=1 state.

Pyrene-dihydrophenazine bis(radical cation) in a singlet ground state.

A new pyrene-dihydrophenazine dyad was prepared. Oxidation of the neutral species produced a bis(radical cation) species, which was characterized by the absorptions of their component radical cations in the visible region. A thermally accessible triplet state was observed in the ESR measurement in frozen n-PrCN. The energy gap between the singlet and triplet states was determined to be 2J/k(B) = -36 +/- 3 K.

Magnetic interaction of tri- and di-oxytriphenylamine radical cation FeCl4 salts.

The tetrachloroferrates of the 2,2':6',2'':6'',6-trioxytriphenylamine (TOT.+.FeCl4-) and 2,2':6',2''-dioxytriphenylamine (DOT.+.FeCl4-) radical cations were prepared, and their structures, magnetic properties, and the relationship between them were investigated. The TOT.+ moiety had a highly planar structure and packed as a dimer surrounded by tetrachroferrates, which also formed a dimer structure. The magnetic properties of TOT.+.FeCl4- were characterized by strong (2J/kB=approximately -1.3x10(3) K, H=-2JS1/2.S1/2) and weak (2J/kB=-1.76 K, H=-2JS5/2.S5/2) antiferromagnetic interactions due to the (TOT.+)2 and (FeCl4-)2 structures, respectively. DOT.+ had a twisted form and no dimer formation was observed between the DOT.+'s and FeCl4-'s. Instead, short contacts between the DOT.+ and chlorine atoms and between the DOT.+'s producing a DOT.+ chain were observed. The magnetic properties of DOT.+.FeCl4- were characterized by a 3D magnetic phase transition to an antiferromagnet with TN=approximately 8 K.