Organic biradical compounds with a mesogenic core and long alkoxy groups: preparation, structures and magnetic properties

Abstract

Series of organic biradical compounds 3a-3h consisting of a mesogenic core (biphenyl, naphthalene, azobenzene and azoxybenzene) and long alkoxy groups with PROXYL or TEMPO radicals were prepared. The TEMPO derivatives (3b, 3d, 3f, and 3h) were found to show fairly large antiferromagnetic interactions (J ¼ À34 $ À45 K) being well expressed by singlet-triplet model irrespective of the mesogenic cores and the behavior is understandable by taking a hand-in-hand like assembled structure into consideration. On the other hand, only weak antiferromagnetic interactions with Curie-Weiss behavior were observed in all of the PROXYL derivatives (3a, 3c, 3e, and 3d) affording a sharp contrast with the TEMPO-based biradicals.

Spin-Carrying Benzoquinone Derivatives

“…The magnetic behavior of compound 7 can be well analyzed by the combination of a Curie−Weiss behavior of antiferromagnetic interaction with a small Weiss temperature (θ = −0.21 K) and a singlet−triplet one of antiferromagnetic interaction with a very large J / k B -value ( J / k B = −154 K) as shown in Figure . Such a large J / k B -value is still rare in nitroxide-based organic radical compounds and is apparently based on the close proximity of a couple of oxygen atoms of nitroxide groups in neighboring molecules and another oxygen atom may contribute to the Curie−Weiss term through the CT interaction.…”

Mesogenic behavior of a 6-oxoverdazyl diradical: towards organic high-spin liquid crystals

“…[15][16][17] Thus, paramagnetic films could be obtained from liquid crystalline radicals, which during the past two decades have become well exemplified in the literature. [18][19][20] Although some mesogenic bi-and tri-radicals have been reported, [21][22][23][24][25][26][27] none of them has coupled spins and exhibits a high spin ground state.…”

Effect of Magnetic and Electric Field on the Orientation of Rare-Earth-Containing Nematics

“…This value can be increased by introducing a stable radical − or paramagnetic metal ions into molecules of liquid crystals. The examples of paramagnetic-metal-containing liquid crystals are mesogenic complexes of copper­(II), − nickel­(II), oxovanadyl, ,, and trivalent ions of rare-earth metals. − The magnetic anisotropy of metallomesogens is a sum of contributions from anisotropies provided by diamagnetic ligands (phenyl groups) and paramagnetic metal ions.…”