Effects of Halo-substitution on 2'-Chloro-5'-halo-phenyl-1,2,3,5-dithiadiazolyl Radicals: A Crystallographic, Magnetic and EPR Case Study

The syntheses and characterization of the aryl-substituted dithiadiazolyls, 2ʹ-Cl-5ʹ- X-C6H3CNSSN• [1 (X = F), 2 (X = Cl), 3 (X = Br), 4 (X = I)] are described. In all four cases the radicals adopt distorted stacks of π*-π* dimers with inter-stack S···X contacts. In 1 (monoclinic P2/c) S···Cl contacts are manifested through a non-crystallographic 3-fold axis forming supramolecular trimers whereas the inter-stack S…X contacts in 2 (triclinic P-1), 3 and 4 (which form an isostructural pair, orthorhombic Pna21) form supramolecular chains. While all the structures adopt π*-π* cis-oid dimer motifs, tuning the halogen modifies the intra-dimer S···S distance. Variable temperature SQUID magnetometry and X-band CW-EPR studies revealed the presence of a thermally accessible triplet state in all cases, with the singlet-triplet separation appearing in the order 1 > 2 > 3 > 4, consistent with a reduction in the overlap integral with increasing intra-dimer S···S separation. Variable temperature structural studies on both 2 and 4 reveal a structural evolution from a distorted π-stack motif towards a regular π-stacked array on warming. This is particularly pronounced in 2 where the intermolecular S…S separations along the stacking direction converge on a regular 3.6 Å spacing at ambient temperature

Crystal Structure and Solid-State Packing of 4-Chloro-5H-1,2,3-dithiazol-5-one and 4-Chloro-5H-1,2,3-dithiazole-5-thione

The crystal structure and solid-state packing of 4-chloro-5H-1,2,3-dithiazol-5-one and two polymorphs of 4-chloro-5H-1,2,3-dithiazole-5-thione were analyzed and compared to structural data of similar systems. These five-membered S,N-rich heterocycles are planar with considerable bond localization. All three structures demonstrate tight solid-state packing without voids which is attributed to a rich network of short intermolecular electrostatic contacts. These include Sδ+…Nδ−, Sδ+…Oδ−, Sδ+…Clδ− and Sδ+…Sδ− interactions that are well within the sum of their van der Waals radii (∑VDW). B3LYP, BLYP, M06, mPW1PW, PBE and MP2 were employed to calculate their intramolecular geometrical parameters, the Fukui condensed functions to probe their reactivity, the bond order, Bird Index and NICS(1) to establish their aromaticity

Access to 1,4-Dihydrobenzo[<i>e</i>][1,2,4]triazin-4-yl Derivatives

A simple, one-pot method for the preparation of 1-aryl-3-phenyl-1,4-dihydrobenzo­[<i>e</i>]­[1,2,4]­triazin-4-yl radicals by addition of aryllithium to the readily available 3-phenylbenzo­[<i>e</i>]­[1,2,4]­triazine followed by aerial oxidation is described. The intermediate anion is also trapped as an <i>N</i>-benzyloxycarbonyl derivative and purified prior to deprotection and oxidation to the radical. The method was demonstrated for nine (het)­arenes, and the regioselectivity of nucleophilic addition to the benzo­[<i>e</i>]­[1,2,4]­triazine and trapping of the intermediate anion with electrophiles was assessed computationally

From Blatter Radical to 7-Substituted 1,3 - Diphenyl-1,4 - Dihydrothiazolo [5′,4′:4,5] Benzo[1,2-e][1,2,4] Triazin-4-yls : Toward Multifunctional Materials

A Blatter radical is oxidized to benzotriazin-7(H)-one which after amination and subsequent acyl- and aroylation gives N-(benzotriazin-6-yl) carboxamides that undergo ring closure with P 2S 5 to afford the corresponding thiazolo[5′,4′:4,5]benzo[1,2-e][1,2,4]triazin-4- yls. These highly delocalized radicals are air stable and show good reversible electrochemical behavior. © 2012 American Chemical Societ

Novel PANK2 mutation in the first Greek compound heterozygote patient with pantothenate-kinase-associated neurodegeneration

Pantothenate-kinase-associated neurodegeneration is the most common autosomal recessive form of neurodegeneration with brain iron accumulation. Less than 100 mutations in PANK2 gene (20p13) are responsible for classic and atypical cases. We report here the first Greek case of atypical pantothenate-kinase-associated neurodegeneration, confirmed by molecular analysis that revealed two trans-acting mutations. Our findings highlight the possible role of rare variants contributing to disease risk and possibly to variable clinical phenotype

Visual attention based region of interest coding for video-telephony applications

Bottom up approaches to Visual Attention (VA) have been applied successfully in a variety of applications, where no domain information exists, e.g. general purpose image and video segmentation. On the other hand, when humans are looking for faces in a scene they perform an implicit conscious search. Therefore, using simple bottom up approaches for identifying visually salient areas in scenes containing humans are not so efficient. In this paper we introduce the inclusion of a top-down channel in the VA architecture proposed in the past (i.e., Itti et al) to account for conscious search in video telephony applications. In such kind of applications the existence of human faces is almost always guaranteed. The regions, in the video-telephony stream, identified by the proposed algorithm as being visually salient are encoded with higher precision compared to the remaining ones. This procedure leads to a significant bit-rate reduction while the visual quality of the VA based encoded video stream is only slightly deteriorated, as the visual trial tests show. Furthermore, extended experiments concerning both static images as well as low-quality video show the efficiency of the proposed method, as far as the compression ratios achieved is concerned. The comparisons are made against standard JPEG and MPEG-1 encoding respectively

Weakening of the pi*-pi* dimerisation in 1,2,3,5-dithiadiazolyl radicals: structural, EPR, magnetic and computational studies of dichlorophenyl dithiadiazolyls, Cl2C6H3CNSSN

A series of dichlorophenyl dithiadiazolyls (DCP-DTDA) have been prepared and structurally characterized by X-ray diffraction (1 = 2,3-DCP-DTDA; 2 = 2,4-DCP-DTDA; 3 = 2,5-DCP-DTDA, 4 = 3,4-DCP-DTDA and 5 = 3,5-DCP-DTDA). All the radicals adopt cis-cofacial π*–π* dimers with intra-dimer SS contacts in the range 3.119(8)–3.300(5) Å. The propensity for chloro-aromatics to adopt a β-sheet structure assists formation of lamellar structures in 1–5 with intra-stack ClCl contacts in the range 3.44(1)–3.82(1) Å. Perpendicular to the stacking direction, the packing is dominated by formation of intermolecular SCl contacts. Variable-temperature magnetic susceptibility measurements on 1–5 in the range 5–300 K reveal the onset of paramagnetism around ca. 200 K. Solid-state EPR studies reveal that this paramagnetism is associated with thermal population of a triplet excited state. A good fit to the Bleaney–Bowers model determined the exchange interactions (2J) between the radicals in the dimers to be in the range −904 to −1529 cm−1. Computational studies of the dimerisation process indicate that at intra-dimer SS distances in excess of 3.2 Å the closed-shell singlet becomes destabilized with respect to both the open-shell singlet and triplet state configurations