Charged Nitronyl Nitroxide Biradicals as Building Blocks for Molecular Ferrimagnetics

Abstract

A crystal-engineering approach to organic ferrimagnetics is reported. Coulombic energy between cationic biradical with S=l and anionic radical with S=1/2 is a promising driving force of co-crystallizing the hetero-molecular assemblage in a controllable manner. As a cationic component of "organic salt femmagnetics", two kinds of nitronyl nitroxide biradicals, 2,6-and 3,5-substituted pyridine derivatives, were examined. It was predicted from semi-empirical molecular orbital calculations that both the 2,6-and 3,5-derivatives have the triplet ground states both in the neutral and cationic states. The molecular ground state of the 2,6-biradical in the neutral state was found to be triplet from magnetic susceptibility measurements, while the susceptibility and ESR measurements suggested a singlet ground state for the 3.5-biradical.

Magnetic Phase Transition in a Heteromolecular Hydrogen-Bonded Complex of Nitronylnitroxide Radicals

“…The magnetic susceptibility of 2 has been reported in ref . Only a monotonic decrease in χ T on lowering the temperature has been observed for the crystalline solid state owing to intermolecular antiferromagnetic interactions.…”

“…An OH···N hydrogen bond between carboxylic acid and pyridine is invoked to cocrystallize two inequivalent open-shell molecular entities with different spin quantum numbers S . An organic acid−base complex 1 (Figure ) has been synthesized, which is composed of a pyridine-substituted biradical 2 and a benzoic acid derivative of monoradical 3 . The biradical 2 is known to have a triplet ( S = 1) ground state .…”

“…The constituent molecules 2 and 3 were synthesized by literature procedures. , Single crystals of the complex 1 were obtained by recrystallization from acetone and pentane solutions.…”

Modulating the Magnetic Properties of Copper(II)/Nitroxyl Heterospin Complexes by Suppression of the Jahn–Teller Distortion

“…20 However 6•2H2O, with the distally methylated co-ligand Me2-3-bpp (Chart 2), shows larger values for J (+50 cm -1 ) and J' (-25 cm -1 ). Hence, 25 but is antiferromagnetic in [Cu(L 2 )2] 2+ . 26 Since the materials were only available in small quantities, these results were investigated by gas phase DF calculations.…”

“…Precedent is provided by 2,6-bis­{3-oxide-1-oxyl-4,4, 5,5-tetramethyl-4,5-dihydro-1 H -imidazol-2-yl}­pyridine (L 2 ), the nitronyl nitroxide analogue of L 1 . J ′{NO···NO} is also ferromagnetic in L 2 but is antiferromagnetic in [Cu­(L 2 ) 2 ] 2+ …”