A MOLECULE LIKE SODIUM

The use of neutral π-radicals as building blocks for molecular conductors holds both appeal and challenge. Such systems obviate the need for counterions, as charge transfer is not required to generate charge carriers. Essentially an array of π-radicals should function like atoms in an elemental metal, e.g., sodium, affording a half-filled energy band. Most radicals, however, tend to dimerize, and even when association can be suppressed the resulting low bandwidth W, coupled with a high on-site Coulomb repulsion U, leads to a Mott insulating state. We are pursuing the design and synthesis of stable heterocyclic thiazyl radicals, with a view to generating stable, crystalline materials with a high W/U ratio. The search for these new radicals, the molecular analogues of sodium, is the subject of this presentation.     

Molecular and crystalline structure of 2-methyl-4,4-diphenyl-5-phenylazo-2-thia-3-aza-4-phosphahepta-2,4-diene-6-one-2-oxide

The molecular structure of 2-methyl-4,4-diphenyl-5-phenylazo-2-thia-3-aza-4-phosphahepta-2,4-diene-6-one-2-oxide has been determined by x-ray crystallography. The sulfur and phosphorus atoms exhibited distorted tetrahedral coordination. The P-N and P=C bond lengths are intnermediate between single and double bond lengths. Delocalization of -electron density was observed in the flattened molecular fragment Ph–N=N–C(=P)–C(=O)–CH₃.Institute of Physiologically Active Substances, Russian Academy of Sciences, 142432 Chernogolovka. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 12, pp. 2737–2741, December, 1992.     

F3CCN5S3, A BICYCLIC MULTIFUNCTIONAL SULFUR-NITROGEN LIGAND

The bicyclic sulfur-nitrogen heterocycle F₃CCN₅S₃ (1) was investigated as a donor and acceptor toward H⁺, metal cations, and F^?. Whereas the protonated species F₃CCN₅S₃H⁺ AsF₆ ^? (2) can be isolated, the product of the reaction with F^? is unstable and decomposes among other products to TAS⁺ F₃CCN₅S₃NC(NH₂)CF₃ ^? (3), which is isolated from this reaction in small amounts.     

Synthesis of Biologically Active 4-Oxo-4H-Chromene Derivatives Containing Sulfur-Nitrogen Heterocycles

The synthesis of 4-oxo-4H-chromenes containing sulfur-nitrogen heterocyclic rings as well as their biological activities are reviewed.     

Alkali Metal Based Triimidosulfite Cages as Versatile Precursors for Single-Molecule Magnets

Based on the potassium [{S(tBuN)₂(tBuNH)}₂K₃(tmeda)-K₃{(HNtBu)(NtBu)₂S}₂] ( 1 ) and sodium precursors [S(tBuN)₃(thf)₃-Na₃SNa₃(thf)₃(NtBu)₃S] ( 2 ), [S(tBuN)₃(thf)₃Na₃{(HNtBu)(NtBu)₂S}] ( 3 ) and [(tmeda)₃S-{Na₃(NtBu)₃S}₂] ( 4 ) the syntheses and magnetic properties of three mixed metal triimidosulfite based alkali-lanthanide-metal-cages [(tBuNH)Dy{K(0.5tmeda)}₂{(NtBu)₃S}₂]_n ( 5 ) and [ClLn{Na(thf)}₂{(NtBu)₃S}₂] with Ln=Dy ( 6 ), Er ( 7 ) are reported. The corresponding potassium ( 1 ) and sodium ( 2 – 4 ) based cages are characterized through XRD and NMR experiments. Preventing lithium chloride co-complexation led to a significant increase of SMM performance to previously reported sulfur-nitrogen ligands. The subsequent Dy^III-complexes 5 and 6 display slow relaxation of magnetization at zero field, with relaxation barriers U=77.0 cm⁻¹ for 5 , 512.9 and 316.3 cm⁻¹ for 6 , respectively. Significantly, the latter complex 6 also exhibits a butterfly-shaped hysteresis up to 7 K.