Molecules

306 KiB

Open AccessArticle

Studies on TMPD:TCNB; a Donor-Acceptor with Room Temperature Paramagnetism and n-π Interaction†

by Prasanna S. Ghalsasi, Brant Cage and J. L. Yarger

Molecules 2004, 9(9), 808-814; https://doi.org/10.3390/90900808 - 31 Aug 2004

Cited by 7 | Viewed by 9790

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Ferromagnetic Organic Radicals)

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528 KiB

Open AccessArticle

Theoretical Studies on Electronic States of Rh-C₆₀. Possibility of a Room-temperature Organic Ferromagnet

by S. Nakano, Y. Kitagawa, T. Kawakami, M. Okumura, H. Nagao and K. Yamaguchi

Molecules 2004, 9(9), 792-807; https://doi.org/10.3390/90900792 - 31 Aug 2004

Cited by 11 | Viewed by 10510

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-C [...] Read more.

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. Full article

(This article belongs to the Special Issue Ferromagnetic Organic Radicals)

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484 KiB

Open AccessArticle

Restricting Magnetic Interaction Pathways in Polyoxometalate Salts of Cationic Nitronyl Nitroxide Free Radicals

by Ana Tarazón, Carlos Giménez-Saiz, Carlos J. Gómez-García and Francisco M. Romero

Molecules 2004, 9(9), 782-791; https://doi.org/10.3390/90900782 - 31 Aug 2004

Cited by 4 | Viewed by 8185

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. Full article

(This article belongs to the Special Issue Ferromagnetic Organic Radicals)

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335 KiB

Open AccessArticle

Synthesis and Magnetic Properties of the Novel Dithiadiazolyl Radical, p-NCC₆F₄C₆F₄CNSSN

by Antonio Alberola, Robert J. Less, Fernando Palacio, Christopher M. Pask and Jeremy M. Rawson

Molecules 2004, 9(9), 771-781; https://doi.org/10.3390/90900771 - 31 Aug 2004

Cited by 35 | Viewed by 10255

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 [...] Read more.

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 μ_B) is temperature independent and inexcellent agreement with the value expected for an S = 1⁄2 paramagnet with g = 2.01(1.74μ_B). The lack of exchange coupling between radicals is attributed to the absence ofsignificant orbital overlap between radical centres. Full article

(This article belongs to the Special Issue Ferromagnetic Organic Radicals)

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758 KiB

Open AccessArticle

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

by Mercè Deumal, Jordi Ribas-Ariño, Michael A. Robb, Joan Ribas and Juan J. Novoa

Molecules 2004, 9(9), 757-770; https://doi.org/10.3390/90900757 - 31 Aug 2004

Cited by 13 | Viewed by 11000

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 [...] Read more.

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 J_^AB 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 Cu_II 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. Full article

(This article belongs to the Special Issue Ferromagnetic Organic Radicals)

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263 KiB

Open AccessArticle

N-Salicylideneamine Derivatives with TEMPO Substituents

by Masayuki Hata, Hiroki Akutsu, Jun-ichi Yamada and Shin’ichi Nakatsuji

Molecules 2004, 9(9), 746-756; https://doi.org/10.3390/90900746 - 31 Aug 2004

Cited by 6 | Viewed by 10130

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Ferromagnetic Organic Radicals)

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288 KiB

Open AccessArticle

The Effects of Conjugation Path Variation on Electron Delocalization in Phenoxyl-Based Systems.

by Yanbing Liu and Paul M. Lahti

Molecules 2004, 9(9), 725-745; https://doi.org/10.3390/90900725 - 31 Aug 2004

Cited by 8 | Viewed by 12315

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Ferromagnetic Organic Radicals)

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299 KiB

Open AccessArticle

New π-Delocalized Persistent Radicals

by Piotr Kaszynski

Molecules 2004, 9(9), 716-724; https://doi.org/10.3390/90900716 - 31 Aug 2004

Cited by 13 | Viewed by 7163

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Ferromagnetic Organic Radicals)

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118 KiB

Open AccessEditorial

“Seek, and ye shall find” (Matthew 7:7)

by Jeremy M. Rawson and Antonio Alberola Catalán

Molecules 2004, 9(9), 713-715; https://doi.org/10.3390/90900713 - 31 Aug 2004

Cited by 1 | Viewed by 4982

Abstract

The preparation and characterisation of organic molecular magnets is a non-trivial task which touches on many contemporary issues within chemistry.[...] Full article

(This article belongs to the Special Issue Ferromagnetic Organic Radicals)

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Molecules, Volume 9, Issue 9 (September 2004) – 9 articles , Pages 713-814

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