The molecular structure of 9,10-diethyl-9,10-diphospha-9,10-dihydroanthracene (PEPP) was determined by X-ray analysis. The central six-membered ring takes a boat conformation with two phosphorus atoms being the stem and stern, and the condensed tricyclic skeleton forms a butterfly-like structure. Of the two ethyl groups, which are attached to two P atoms in the central ring, the one is placed toward outside the skeleton (extra), and the other is located toward the inside of the ‘butterfly’ (intra). The observed redox potential of 0.63 V vs. Ag/AgCl suggests that this molecule has a fairly good electron-donating characteristics. From the spectroscopic observation and a quantum-chemical calculation, the donating orbital is estimated to be that of lone pair electrons at the P atom that attaches to the intra ethyl group.

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A couple of TEMPO-substituted anthraquinone isomers showed marked difference regarding solvating properties and the resulting magnetic behavior: without obstruction an isomer includes solvent molecules as benzene or acetonitrile to form crystals exhibiting different intermolecular magnetic interactions, while another isomer gives solvent-free crystals showing singlet-triplet behavior.Since the first discovery of a purely organic ferromagnet, -phase crystal of p-nitrophenyl nitronyl nitroxide radical with a Tc-value of 0.60 K, in 1991 [1], much attention has been paid to the development of new organic radical crystals based mainly on aminoxyl (nitroxyl or nitroxide) radicals, such as nitroxyl nitroxide or TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) radicals [2]. The increase in Tc-value to 1.48 K was next attained in N, N'-dioxy-1,3,5,7-tetramethyl-2,6diazaadamantane in 1993 [3] but, since then, no steep increase in Tc-value could be realized in any organic radical crystal-based on aminoxyls.accepting property, with an aminoxyl group, having electron-donating property [7], would result in the formation of intriguing supramolecular structures in the radical crystals. Additionally, our intention was to use the anthraquinones as building blocks for CT complex formation or redox materials.In this paper we wish to report on the preparation of a couple of TEMPO-substituted anthraquinone isomers (1 and 2) prepared for the purpose, and the marked difference, of their magnetic properties depending on the variation of their packing features, i.e., supramolecular structures. O O O C O N O O O O C O N O 1 2In recent years rather, considerable attention has been turned to the development of organic multifunctional magnetic materials [4], and we have also turned our interest towards developing organic multifunctional spin systems with photo-functionality, heat-responsive properties or conductivity by using aminoxyl radicals as the building blocks [5].The isomers were prepared by conventional esterification of 1-or 2-hydroxyanthraquinone with 4-carboxy-TEMPO biradical by using DCC and DMAP and were isolated both as powdery materials in 31% for 1 and 47 % for 2, respectively. The magnetic susceptibility data were taken by SQUID susceptometer between the temperature range from 2 K to 300 K and the data for a powder sample of 1-position isomer 1 showed the existence of weak ferromagnetic intermolecular interactions with Curie-Weiss behavior between the radical spins (Table 1).Nevertheless, it is still noteworthy to investigate structure/magnetic properties of certain classes of organic radical compounds [6] to develop and design organic magnetic materials with exotic magnetic properties and possible organic ferromagnets. We then initiated the preparation of anthraquinone derivatives with aminoxy substituents to see their structure/magnetic property relations. This was performed with the expectation that the combination of an anthraquinone moiety, having electronRecrystallization of the isomer from benzene gave orange needles and ...

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