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Special Issue "Ferromagnetic Organic Radicals"

A special issue of Molecules (ISSN 1420-3049).

Deadline for manuscript submissions: closed (1 September 2004)

Special Issue Editors

Published Papers (9 papers)

Jeremy M. Rawson and Antonio Alberola Catalán Editorial: “Seek, and ye shall find” (Matthew 7:7) Molecules 2004, 9(9), 713-715; doi:10.3390/90900713 Received: 7 July 2004 / Accepted: 1 August 2004 / Published: 31 August 2004 Show/Hide Abstract | Download PDF Full-text (118 KB) Abstract: n/a

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Piotr Kaszynski Article: New π-Delocalized Persistent Radicals Molecules 2004, 9(9), 716-724; doi:10.3390/90900716 Received: 7 May 2004 / Accepted: 1 June 2004 / Published: 31 August 2004 Show/Hide Abstract | Download PDF Full-text (299 KB) Abstract: Progress in the theoretical and experimental investigation of heterocyclic radicals suitable for incorporation into the structure of a liquid crystalline molecule is described. Five classes of heterocyclic systems are discussed, including their methods of preparation, stability and further functionalization to form potentially mesogenic materials.

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Yanbing Liu and Paul M. Lahti Article: The Effects of Conjugation Path Variation on Electron Delocalization in Phenoxyl-Based Systems. Molecules 2004, 9(9), 725-745; doi:10.3390/90900725 Received: 23 April 2004 / Accepted: 2 June 2004 / Published: 31 August 2004 Show/Hide Abstract | Download PDF Full-text (288 KB) Abstract: A number of persistent 2,6-di-tert-butylphenoxyl based radicals were synthesized as models for unpaired spin delocalization as a function of conjugation pathway, and were investigated by ESR and UV-vis spectroscopy. Phenoxyl spin delocalizes significantly onto a para-phenyl ring, but further delocalization through a meta-vinyl or meta-carbonyl linkage is not detectable by ESR hyperfine coupling. UV- vis spectra do show a red shift of the longest wavelength transition for a carbonyl-type substituent by comparison to a vinyl substituent in the meta-position of a para-phenyl group. By comparison, a para-styryl substituent on the phenoxyl causes very large spin delocalization from the phenoxyl unit, with the largest hyperfine coupling being found on the ethenyl unit of the assemblage. This large delocalization accounts for the reactivity of radicals that incorporate such units.

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Masayuki Hata, Hiroki Akutsu, Jun-ichi Yamada and Shin’ichi Nakatsuji Article: N-Salicylideneamine Derivatives with TEMPO Substituents Molecules 2004, 9(9), 746-756; doi:10.3390/90900746 Received: 25 April 2004 / Accepted: 21 May 2004 / Published: 31 August 2004 Show/Hide Abstract | Download PDF Full-text (263 KB) Abstract: Three N-salicylideneamine derivatives bearing TEMPO (2,2,6,6-tetra- methyl-1-piperidinyloxy) substituents were prepared in order to study their structure and property relationships and to investigate the possibilities of the existence of heat and/or light responsive magnetic properties. Curie-Weiss behavior with weak ferromagnetic intermolecular spin-spin interactions was observed in one of the radicals, while antiferromagnetic interactions were predominant for the other radicals and the structure-property relationships were investigated for the radical compounds from their crystal structures obtained by X-ray analyses. Preliminary results of the examination of their responses towards light and heat are also described.

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Mercè Deumal, Jordi Ribas-Ariño, Michael A. Robb, Joan Ribas and Juan J. Novoa Article: A First-Principles Analysis of the Magnetism of CuII Polynuclear Coordination Complexes: the Case of [Cu4(bpy)4(aspartate)2(H2O)3](ClO4)4•2.5H2O Molecules 2004, 9(9), 757-770; doi:10.3390/90900757 Received: 8 April 2004 / Accepted: 1 May 2004 / Published: 31 August 2004 Show/Hide Abstract | Download PDF Full-text (758 KB) Abstract: The magnetic structure of the [Cu4(bpy)4(aspartate)2(H2O)3](ClO4)4·2.5 H2Ocrystal — using fractional coordinates determined at room-temperature — has beenanalysed in detail. This analysis has been carried out by extending our first principlesbottom-up theoretical approach, which was initially designed to study through-spacemagnetic interactions, to handle through-bond magnetic interactions. The only input datarequired by this approach are the values of the computed JAB exchange parameters for allthe unique pairs of spin-containing centres. The results allow the magnetic structure ofthe crystal, which presents two types of isolated tetranuclear CuII clusters, to be definedin quantitative terms. Each of these clusters presents ferro and antiferromagneticinteractions, the former being stronger, although outnumbered by the latter. Thecomputed magnetic susceptibility curve shows the same qualitative features as theexperimental data. However, there are small differences that are presumed to beassociated with the use of room-temperature crystal coordinates.

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Ana Tarazón, Carlos Giménez-Saiz, Carlos J. Gómez-García and Francisco M. Romero Article: Restricting Magnetic Interaction Pathways in Polyoxometalate Salts of Cationic Nitronyl Nitroxide Free Radicals Molecules 2004, 9(9), 782-791; doi:10.3390/90900782 Received: 1 June 2004 / Accepted: 17 June 2004 / Published: 31 August 2004 Show/Hide Abstract | Download PDF Full-text (484 KB) Abstract: Salts 1 and 2 that combine the [W6O19]2- Lindqvist anion with the cationicnitronyl nitroxide (NN) free radicals p-MepyNN+ and nBu3NCH2NN+ , respectively, havebeen synthesized and their structural and magnetic properties have been studied.

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Antonio Alberola, Robert J. Less, Fernando Palacio, Christopher M. Pask and Jeremy M. Rawson Article: Synthesis and Magnetic Properties of the Novel Dithiadiazolyl Radical, p-NCC6F4C6F4CNSSN Molecules 2004, 9(9), 771-781; doi:10.3390/90900771 Received: 23 May 2004 / Accepted: 21 June 2004 / Published: 31 August 2004 Show/Hide Abstract | Download PDF Full-text (335 KB) Abstract: The dithiadiazolyl radical p-NCC6F4C6F4CNSSN• (4) retains its monomericnature in the solid state with molecules linked together into chains via supramolecularCN···S interactions. Variable temperature magnetic studies on 4 show that it behaves as anear-ideal Curie paramagnet (|θ| less than 0.1 K), indicating negligible intermolecularexchange. The effective magnetic moment (1.78 μB) is temperature independent and inexcellent agreement with the value expected for an S = 1⁄2 paramagnet with g = 2.01(1.74μB). The lack of exchange coupling between radicals is attributed to the absence ofsignificant orbital overlap between radical centres.

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S. Nakano, Y. Kitagawa, T. Kawakami, M. Okumura, H. Nagao and K. Yamaguchi Article: Theoretical Studies on Electronic States of Rh-C60. Possibility of a Room-temperature Organic Ferromagnet Molecules 2004, 9(9), 792-807; doi:10.3390/90900792 Received: 1 April 2004 / Accepted: 3 May 2004 / Published: 31 August 2004 Show/Hide Abstract | Download PDF Full-text (528 KB) Abstract: A possible mechanism for a ferromagnetic interaction in the rhombic (Rh) formof C60 (Rh-C60) is suggested on the basis of theoretical studies in relation to cage distortionof the C60 unit in the polymerized 2D-plane. Band structure calculations on Rh-C60 showthat cage distortion leads to competition between diamagnetic and ferromagnetic states,which give rise to the possibility of thermally populating the ferromagnetic state.

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Prasanna S. Ghalsasi, Brant Cage and J. L. Yarger Article: Studies on TMPD:TCNB; a Donor-Acceptor with Room Temperature Paramagnetism and n-π Interaction† Molecules 2004, 9(9), 808-814; doi:10.3390/90900808 Received: 1 June 2004 / Accepted: 3 August 2004 / Published: 31 August 2004 Show/Hide Abstract | Download PDF Full-text (306 KB) Abstract: A donor-acceptor compound based on N,N,N′,N′-tetramethyl-p-phenylene-diamine and 1,2,4,5-tetracyanobenzene (TMPD:TCNB) has been synthesized. The crystalstructure of the black 1:1 complex formed between TMPD and TCNB has beendetermined by single crystal X-ray diffraction at room temperature. The compoundcrystallizes in the triclinic space group P-1 with cell dimensions: a = 7.4986(15) å, b =7.6772(11) å, c = 8.0764(15) å, α = 78.822(12)°, β = 83.3779(19)°, γ = 86.289(17)°.TMPD and TCNB molecules are stacked alternately in infinite columns along the a-axis.The structure does not seem to show the usual π-π interaction between the two aromaticrings, but indicates an n-π interaction localized between the nitrogen atoms of the donorand the cyano groups of the acceptor.

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Last update: 18 August 2008