Magnetism has fascinated and served humanity for
almost 3000 years. Since the discovery of the lodestone
(FeO-Fe_2O_3), many different magnetic materials
have been developed, almost all based on transition
metals and/or rare-earth elements. Technological application
of magnetism also has a long history, from the compass to today's sophisticated magnetic memory systems. In contrast, the theory of magnetism has progressed more slowly, despite the efforts of great minds throughout history. The reason early theoretical models were not very valuable is now clear. Any viable theory of magnetism must be based on two inherently quantum mechanical concepts: electron spin and the Pauli exclusion principle. As such, only the 20th century has produced a competent model for magnetism,
and that model continues to evolve. Studies over the
last 20 years have revealed a bewildering array of new
magnetic phenomena that continue to challenge our
understanding of solid-state physics.

Spin control in organic molecules

http://lib.fibopt.ru/Articles/PAPER/Elsevier/CCRev-2007-251-1007.pdf

Stretching bonds in main group element compounds—Borderlines between biradicals and closed-shell species

A large number of thermal and photochemical reactions proceed via biradical intermediates. Typically, a biradical generated in the triplet state must first undergo intersystem crossing (ISC) to the singlet biradical before forming products. This presents one of the major challenges of photochemistry; to understand a reaction in which the molecule must hop from one potential energy surface to another. In this Account we are concerned with triplet-derived flexible chain biradicals, and Scheme I shows the important processes. A triplet precursor (e.g., an {sup 3}n, {pi}* ketone) cleaves with conservation of spin to produce a triplet biradical in a set of conformations where the radical centers are close together. Two processes ensue: ISC in a given conformation produces a singlet biradical in the same conformation, and internal rotation gives rise to chain dynamics, which changes the end-to-end distance.

Dynamics of flexible triplet biradicals

Radical ions generated by electron transfer reactions are known as important intermediates in organic chemistry. On the other hand, their formation, recombination and transport in organic materials is responsible for a series of attractive physical properties. Radical ion formation is often accompanied by structural changes being well understood in small organic molecules, which also constitute repeating units of intensively studied macromolecules. Therefore, an approach is described herein to compare and combine the structural and energetic description of monomeric and oligomeric radical ions with that of partially oxidized or reduced polymeric materials.

Radical ions - where organic-chemistry meets materials sciences

The assembly of a new family of [(η5-C5Me5)MoS3Cu3]-supported supramolecular compounds from a preformed cluster [PPh4][(η5-C5Me5)MoS3(CuNCS)3]·DMF (1·DMF) with four multitopic ligands with different symmetries is described. Reactions of 1 with 1,2-bis(4-pyridyl)ethane (bpe) (Cs symmetry) or 1,4-pyrazine (1,4-pyz) (D2h symmetry) in aniline gave rise to two polymeric clusters {[{(η5-C5Me5)MoS3Cu3}2(NCS)3(μ-NCS)(bpe)3]·3aniline}n (2) and [(η5-C5Me5)MoS3Cu3(1,4-pyz)(μ-NCS)2]n (3). On the other hand, solid-state reactions of 1 with 2,4,6-tri(4-pyridyl)-1,3,5-triazine (tpt) (D3h symmetry) or 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphyrin (H2tpyp) (D4h symmetry if 21H and 23H of the H2tpyp are omitted) at 100 °C for 12 h followed by extraction with aniline yielded another two polymeric clusters {[(η5-C5Me5)MoS3Cu3(tpt)(aniline)(NCS)2]·0.75aniline· 0.5H2O}n (4) and {[(η5-C5Me5)MoS3Cu3(NCS)(μ-NCS)(H2tpyp)0.4(Cu−tpyp)0.1]·2aniline·2.5benzene}n (5). These compounds were characterized by elemental analysis, IR spectra...

Construction of [(η5-C5Me5)MoS3Cu3]-Based Supramolecular Assemblies from the [(η5-C5Me5)MoS3(CuNCS)3]- Cluster Anion and Multitopic Ligands with Different Symmetries

2,4-Dimethylene-1,3-cyclobutadiyl

Observation directe de l'etat triplet du compose cite dans le titre par spectroscopie RPE et etude de ses comportements thermiques

Gary J. Snyder

Papers

2,4-Dimethylene-1,3-cyclobutadiyl

Direct, ESR observation of the localized biradical 1,3-dimethyl-1,3-cyclobutadiyl

Electronic spectroscopy of a non-Kekule isomer of benzene, 2,4-dimethylene-1,3-cyclobutanediyl

Electronic Spectroscopy of a Non‐Kekulé Isomer of Benzene, 2,4‐Dimethylene‐1,3‐cyclobutanediyl

Direct, esr observation of the localized biradical 1,3-dimethyl-1,3-cyclobutadiyl