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C 16 H 22 S 2 cristallise dans P2 1 /n avec a=8,851, b=15,398 et c=11,590 A, Z=4; affinement jusqu'a R=0,036. Presence de quatre contacts intramoleculaires entre les atomes H et le cycle phenylene dans le domaine 2,53 a 2,68 A, contribuent au «benzene courbe» typique des paracyclophanes

The Ru atom of the title complex, [Ru(C10H8N2)2-(H2O)2](PF6)2, is located on a crystallographic inversion center; the bipyridine ligands are bowed [dihedral angle between C5N planes is 162.68 (12) degrees] due to the interligand steric interactions of the trans bipyridyl units. The Ru--O distance is 2.116 (2) A and the mean Ru--N distance is 2.074 (2) A.

Sublimation of 1,2,3,5-dithiadiazolyl in vacuo affords a triclinic phase of the dimer [HCN2S2]2. The crystals belong to the space group P¯1, a = 6.816(3), b = 13.940(2), c = 14.403(3) Å, α = 116.830(14), β = 98.64(3), γ = 99.18(3)°, FW = 212.4 (for [HCN2S2]2·[N2]0.08) Z = 6. The crystal structure consists of stacked dimers, with three dimers per asymmetric unit. Pairs of asymmetric units, related by an inversion center, generate a pinwheel motif consisting of six dimers. The columnar structure associated with these pinwheels forms close-packed sets of “molecular tubes”. Cosublimation of the radical in the presence of iodine in the mole ratio (HCN2S2:I = 5:1) yields an iodine-doped hexagonal phase of composition [HCN2S2]6[I]1.1. Crystals of this material belong to the space group P61, a = b = 14.132(16), c = 3.352(5) Å, FW = 128.20, Z = 6. The crystal structure consists of sixfold pinwheels in which the now evenly spaced HCN2S2 rings form a spiral about the 61 axis. The iodine atoms lie within the columnar cavity of the pinwheels in a disordered array wrapped tightly about the sixfold screw axis. The single-crystal conductivity of the doped material is 15 S cm-1 at room temperature. Raman spectroscopic and magnetic susceptibility measurements on the doped material are reported.

The reaction of oxamidrazone with sulfur dichloride affords 4,4'-bis(1,2,3,5-dithiadiazolium) dichloride, which can be reduced with triphenylantimony to the corresponding bis(1,2,3,5-dithiadiazolyl) diradical; the solid state structure and transport properties of the dimer [S2N2CCN2S2]2 are reported.

The 1:1 reaction of the heterocyclic radicals [PhCN2E2]∙ (E = S, Se) and iodine affords the mixed valence salts [PhCN2E2]3[I3], while reaction of PhCN2S2 with an excess of iodine affords the simple salt [PhCN2S2][I3]; the solid-state structures of these complexes have been determined by X-ray crystallography. Crystals of both of the mixed valence compounds belong to the triclinic space group P¯1; for E = S, a = 10.278(4), b = 11.508(2), c = 13.333(4) Å, α = 114.97(2), β = 99.21 (3), γ = 92.65(2)°, FW = 308.15, Z = 6; for E = Se, a = 10.368(6), b = 10.818(8), c = 13.421(8) Å, α = 80.64(5), β = 81.20(5), γ = 75.18(6)°, FW = 401.95, Z = 6. Crystals of the simple salt belong to the monoclinic space group P21/a; a = 7.366(4), b = 11.734(1), c = 15.166(2) Å, β = 95.92(3)°, FW = 1303.99(7), Z = 4. In each of the mixed valence compounds the molecular (asymmetric) unit consists of a trimeric [PhCN2E2]3+ cation and an associated triiodide anion. Within the cations the mean interannular E-E contacts are 3.181/3.377 Å (E = S/Se). The packing patterns of the two compounds show important differences. For E = S the crystal structure does not exhibit stacking of the trimeric molecular building blocks, but for E = Se the trimer units form dovetailed stacks in which consecutive layers are oriented in a trans-antipodal fashion. This arrangement introduces close interannular contacts between the blocks along the stack, as well as close lateral contacts. The asymmetric unit of [PhCN2S2][I3] consists of a single PhCN2S2+ cation and an associated triiodide anion; there are no unusual stacking features. The magnetic and conductivity properties of [PhCN2Se2]3[I3] are reported, and the results discussed in the light of extended Hückel band structure calculations.

MOST molecular conductors rely on charge transfer to create carriers. For example, the ET salts1 are hole-doped whereas the C60 salts2 are electron-doped. Neutral radical species in which bands are formed by π-orbital overlap would be expected to have half-filled bands and thus to be conducting3, but no such metals have yet been reported. Here we report the synthesis and characterization of a molecular conductor which combines both of these approaches: energy bands are formed from one-dimensional stacks of neutral π-radicals, and the material is rendered conducting by electron transfer from the conduction band following doping with an acceptor. The radical species is the l,4-phenylene-bis(dithiadiazolyl) diradical 1,4-[(S2N2C)C6H4(CN2S2)] (2 in Fig. 1), reaction of which with iodine vapour leads to crystals of [2][I]. At low temperatures this compound is essentially a diamagnetic insulator, but above 200 K the conductivity and magnetic susceptibility increase markedly, and at room temperature the conductivity reaches l00 S cm−1, which is comparable to that shown by conventional molecular charge-transfer salts.

The preparation and solid-state characterization of the bifunctional radicals [4,4’-(5-cyanobenzene)-1,3-bis(1,2,3,5-dithiadiazolyl)] and [4,4’-(5-cyanobenzene)-1,3-bis( 1,2,3,5-diselenadiazolyl)] [5-CN-1,3-C6H3(CN2E2)2] (E = S, Se) are described. The crystals of the two title compounds are isomorphous and belong to the monoclinic space group P21/c, with (for E = S) a = 7.00(2), b = 30.050(6), c = 10.713(8) A, β = 104.80(10)°, V = 2179(6) A3, Z = 8 and (for E = Se) a = 7.124(4), b = 30.50(2), c = 10.874(2) A, β = 105.46(3)°, V = 2277(2) A3, Z = 8. The crystal structures consist of stacks of diradicals running parallel to x; radical dimerization up and down the stack generates a zigzag arrangement, as seen in the related 1,3-phenylene structures. Along the stacking axis the mean intradimer E-E contacts are 3.12 (E = S) and 3.23 A (E = Se), while the mean interdimer E- - -E distances are 3.89 (E = S) and 3.91 A (E = Se). Magnetic and conductivity data are presented and discussed in light of extended Huckel band structure calculations.

The preparation and solid-state characterization of the trifunctional radical 1,3,5-benzenetris(1,2,3,5-dithiadiazolyl) [4,4’,4”-(1,3,5-benzenetriyl)tris[1,2,3,5-dithiadiazolyl], 1,3,5-C6H3(CN2S2)3] are described. The crystals belong to the monoclinic space group P21/c, with a = 6.927 (2), b = 19.798 (3), c = 19.393 (3), and β = 99.80 (2) A3. The crystal structure consists of stacks of triradicals running parallel to x. Each radical center associates with a neighboring radical, generating alternating long (mean 3.832 A) and short (mean 3.117 A) interradical S···S contacts along the stack; only two of the three crystallographically distinct bond alternation waves so generated are in-phase. The packing of triradical stacks produces an extensive network of close interstack S···S contacts. The compound is diamagnetic at room temperature, but paramagnetic defects begin to appear near 450 K. The room-temperature single-crystal conductivity is near 10-7 S cm-1. Extended Huckel band structure calculations reveal a band gap of 0.8 eV.

Previous research has established dentistry as a growth sector of the U.S. economy. This study examines the economic relationship between dentistry's growth and factors operating on the demand and supply sides of the dental market. Output, defined as real per capita dental expenditures, was hypothesized to be a function of consumer income, dental insurance and the supply of dentists. Data for the period 1950-89, were analyzed using a generalized least squares approach. The analysis supported the hypothesis, indicating a significant relationship between growth in the dental sector and economic market factors. The study concludes that dentistry's real growth since 1950 was: (1) induced by increases in demand, mainly attributable to insurance and to a lesser extent consumer incomes; and (2) supported by increases in supply. The findings provide support for the insurance hypothesis, which suggests that growth in dental insurance has had a significant impact on the dental economy in recent years.

Cloud-top heights were successfully derived from reflected solar radiation measurements within the oxygen A-band absorption. The accuracy of the estimated cloud-top heights was to within 40 meters over stratus clouds when compared with simultaneously taken lidar measurements. Estimations of the cloud optical thickness from reflected radiances at λ = 755 nm are reasonable. Between both cloud optical thickness and cloud-lop height a positive cross correlation was found to be significant at scales up to 5 km, which confirms a relationship between cloud-top height and cloud optical thickness. These experimental musts show the potential of multichannel radiance measurements for the detection of physical cloud properties.

C 24 H 20 ClN 3 P 2 Se cristallise dans P1 avec a=9,759, b=11,046, c=13,332 A, α=65,50, β=64,89, γ=74,96 o , Z=2; affinement jusqu'a R=0,036. Dans le cycle a 5 chai←nons, l'un des liens entre P et N est presque plan (a 0,053 A pres), tandis que l'atome Se soit de ce plan de 0,499 A du cote du chlore. Les longueurs des liaisons de la sequence Se−N−P−N sont en moyenne de 1,730; 1,637 et 1,584 A. Les angles des liaisons du cycle autour des atomes Se et P sont respectivement de 111,5 o et 117,8 o

Effective software measurement enhances the software development environment. One aspect of software measurement that merits additional exploration is the pre-design phase. Research during the past two decades has shown the importance of the requirements engineering phase of the software development process. As a complement to the increased emphasis on the requirements engineering environment, we to investigate properties of the requirements phase that can provide information on the difficulty of the problem to be solved by the proposed software system. In this paper, we develop measurements that provide a characterization of the difficulty of the proposed system at the early stage of requirements definition. The characterization measurements are from an object-oriented perspective. They are based on solution objects, actions, and the level of interaction among the objects. We describe an automated tool that generates the information needed to evaluate the measurements. These characterizations provide objective measures that can be used as input to the early evaluation of problem difficulty that is required when cost and time estimates must be formulated.

The two termini of the torsionally strained dithiadiazolyl diradical S2N2C–C6H3Me–MeC6H3–CN2S2 3 possess different solid state structural environments; the bulk magnetic susceptibility of 3 is interpreted in terms of the distinct properties of the two radical centres.

The synthesis and crystal structure of 2,5-diamino-3,6-dichloropyrazine, C4H4Cl2N4, are described. The centrosymmetric molecule has an exocyclic C—N distance of 1.362 (3) A, and a nearly planar amine group [the angles at N sum to 351 (2)°]. Within the crystal, the molecules form a ribbon through two centrosymmetric pairs of N—H⋯N hydrogen-bond interactions, where the N⋯N distance is 3.110 (3) A.

A crystallographic twofold rotation axis passes through the C-C bond joining the imidazole rings of the title compound, C10H10N4O2. The molecule crystallizes in a cis disposition. The planar acetyl group is twisted by 5.0 (3)° with respect to the imidazole ring and the two imidazole rings are tilted by 60.53 (5)° in relation to one another.

The title molecules, C 6 H 4 N 6 O 4 .2C 3 H 7 NO, lie on a center of inversion. One N atom of the ring is hydrogen bonded to the O atom of the dimethylformamide (DMF) solvate molecule [N-H...O = 2.699 (4) A]. The nitro group is tilted by 4.11 (18)° with respect to the imidazole ring.

Ru(HSO3)2(NH3)4), Mr=331.3, mono- clinic, P21/c, a = 6.2019 (15), b = 7.0213 (11), c = 11.761 (2)A, fl= 115.30(2) °, V= 463.0 (3) A 3, Z= 2, Dx = 2-38 g cm -3, A(Mo Kte) = 0.71073 A,, /z = 21-0 cm- 1, F(000) = 332, T = 293 K, R = 0.019 for 1179 reflections with Fo 2 > 3o'(Fo2). The complex lies on an inversion center with Ru-N distances of 2.141 (2) A, and a Ru-S distance of 2-2785 (5) A.. All of the H atoms are linked to O atoms of neighboring hydrogensulfite ligands in an extensive network of H bonds. Experimental. The title complex (I) was obtained by the procedure described by Vogt, Katz & Wiberley (1965). Colorless crystals were obtained by slow cooling of the reaction mixture. Data crystal was 0.12 x 0-20 x 0-32 mm and was mounted with epoxy on a glass fiber. Intensities measured with an Enraf- Nonius CAD-4 diffractometer using o~--20 scans of 4-16 ° min-~ in 0. Unit cell determined from least- squares analysis of angle data for 25 reflections with 17 < 20 < 22 °. Analytical absorption correction varied from 0-79 to 1.00. Data collected to (sin0)/A =0.68A.-', 0_

K[RuCl 4 (C 10 H 8 N 2 )] cristallise dans Pbcn avec a=14,382, b=13,980 et c=7,491 A, Z=4; affinement jusqu'a R=0,051. L'anion [Ru(bpy)Cl 4 ] − est sur un axe cristallographique d'ordre 2. Les cycles organiques des anions voisins se recouvrent avec des espacements entre les plans 3,27 et 3,36 A

Preparation du complexe trans-[Ru(phen) 2 (OH 2 ) 2 ]PF 6 par photolyse du cis en solution aqueuse de HPF 6 . Par substitution thermique de coordinats, formation de trans-[Ru(phen) 2 (CH 3 CN)(OH 2 )](PF 6 ) 2 , trans-[Ru(phen) 2 (CH 3 CN) 2 ](PF 6 ) 2 et trans-[Ru(phen) 2 (py) 2 ](PF 6 ) 2 . Isomerisation des trans en cis. Structure cristalline

Preparation et etude par spectrometrie RMN des composes N 3 P 3 F 4 (C 6 H 5 )R(R=N(CH 3 ) 2 , n-C 4 H 9 ,t-C 4 H 9 ). Le compose avec R=t−C 4 H 9 cristallise dans le systeme orthorhombique, groupe Pmma et sa structure est affinee jusqu'a R=0,042

An expedient synthesis of previously unknown (1 Z , 3 Z )-1, 4-dibromobutadiene is reported. When this dibromide is treated with s- or t-butyllithium, (1 Z , 3 Z )-1-bromo-4-lithio-butadiene is generated. Treatment of the dibromide with four equivalents of t-butyllithium gives (1 Z , 3 Z )-dilithiobutadiene. Reaction of (1 Z , 3 Z )-1-bromo-4-lithiobutadiene with (η 5 -C 5 H 5 )Fe(CO) 2 I gives (1 Z , 3 Z )-(η 5 -C 5 H 5 )Fe-(CO) 2 CH=CHCH=CHBr. X-ray crystallographic analysis of this latter compound establishes the geometry about the bromobutadiene ligand.

Cristallisation dans le groupe P2 1 /c avec a=9,216, b=14,318 et c=10,229 A, β=104,57°, Z=4. Affinement jusqu'a R=0,037. La molecule est formee d'une unite norbornenyl avec deux groupes S 3 N attaches de facon exo aux positions 2,3. Effets des differents substituants sur l'energie de transition π*→π* des derives X-S 3 N

The cation trans -[Ru(bpy) 2 (PPh 3 ) 2 ] 2+ and trans -[Ru(Me 2 bpy 2 ) 2 (py) 2 ] 2+ both contain bipyridine ligands which are distorted because of the crowding of the two chelate units. The hexafluorophosphate salt of the first cation crystallizers in space group P2 1 /n, with a = 11.630(1), b = 20.245(2), c = 11.299(1)A, &#x03B2 = 103.99(1)°, and Z = 2. R = 0.047 for 2396 observed reflections. The hexafluorophosphate salt of the second cation crystallizers in space group C2/m, with a = 18.392(2), b = 11.265(1), c = 13.383(1)A, &#x03B2 = 139.42(2)°, and Z = 2. R = 0.047 for 1403 observed reflections. The Ru of the first cation lies on an inversion center and the Ru of the second cation lies on a special position of 2/m symmetry. The distortions of a number of bipyridine complexes with the trans geometry are analyzed and found to fall into two categories, bowed or twisted. The two complexes of this report were found to have a bowed conformation.

The oxidation of the cofacial dimer (I), which is in equilibrium with its remarkably stable radical (II), with nitrosonium salts yields the corresponding salts (III).

Cristallisation dans le groupe P2 1 /n avec a=6,563, b=11,717 et c=11,409 A, β=101,63 °, Z=4. Affinement jusqu'a R=0,042. Le cation S 4 N 4 H + se presente sous forme de cycle a 8 chainons en conformation bateau. Discussion a partir de calculs MNDO du rearrangement structural induit par la protonation de S 4 N 4

Preparation de complexes du ruthenium (II) de type ru(bpy) 2 (HSO 3 )L ou L=H 2 O, SO 3 2− , pyridine et bpy-bipyridine. Etude en solution par voltammetrie cyclique et equilibres acidobasiques. Etude radiocristallographique

The oxidation of the S/sub 3/N/sub 3//sup -/ ion in acetonitrile solution by molecular oxygen gives rise to four major products: S/sub 4/N/sub 5//sup -/, S/sub 4/N/sub 5/O/sup -/, S/sub 3/N/sub 3/O/sup -/, and S/sub 3/N/sub 3/O/sub 2//sup -/. The relative yields of these species are a function of the flow rate of oxygen, and the progress of the reaction and the structure of the various ions in solution can be analyzed by using /sup 15/N NMR spectroscopy. The crystal and molecular structures of (Ph/sub 3/P)/sub 2/N/sup +/S/sub 3/N/sub 3/O/sup -/ and (Ph/sub 3/P)/sub 2/N/sup +/S/sub 3/N/sub 2/O/sub 2//sup -/ have been determined by x-ray diffraction. Crystals of the former are monoclinic, space group P2/sub 1//c, with a = 17.161 (2) A, b = 9.970 (1) A, c = 20.591 (2) A, ..beta.. = 104.45 (1)/sup 0/, V = 3411.7 A/sup 3/, and Z = 4. Crystals of the latter are monoclinic, space group P2/sub 1/, with a = 12.421 (1) A, b = 13.036 (1) A, c = 10.699 (1) A, ..beta.. = 103.36 (1)/sup 0/, V = 1685.6 A/sup 3/, and Z = 2. Both structures were solved by direct methods and refined by full-matrix least-squares procedures; formore » (Ph/sub 3/P)/sub 2/N/sup +/S/sub 3/N/sub 3/O/sup -/ the final R = 0.053 and R/sub w/ = 0.075 for 3058 reflections with I > 3sigma(I), and for (Ph/sub 3/P)/sub 2/N/sup +/S/sub 3/N/sub 3/O/sub 2//sup -/ the final R = 0.048 and R/sub w/ = 0.057 for 2312 reflections with I > 3sigma(I). The two anions S/sub 3/N/sub 3/O/sup -/ and S/sub 3/N/sub 3/O/sub 2//sup -/ both possess six-membered S/sub 3/N/sub 3/ ring structures with exocyclic oxygen atoms bonded to sulfur (in S/sub 3/N/sub 3/O/sub 2//sup -/ the oxygens are geminally substituted). Both rings exhibit significant variations in chemically equivalent bond lengths and angles. The visible spectra of S/sub 3/N/sub 3/O/sup -/ (lambda/sub max/ = 509 and 340 nm) and S/sub 3/N/sub 3/O/sub 2//sup -/ (lambda/sub max/ = 562 and 362 nm) are interpreted in terms of the expected perturbations on the ..pi..-manifold of the S/sub 3/N/sub 3//sup -/ anion; the observed absorptions are assigned to ..pi..* ..-->.. ..pi..* type excitations. 34 references, 5 figures, 6 tables.« less

Crystals of the title sulfur compound are orthorhombic, Cmca, with a=9.872 (1), b=9.594 (1), and c=15.488 (1) A, V=1467.0 (4) A3, Z=4, and Dc =1.38 g cm−2. The final refinement using 537 observed reflections for 57 variable gave R=0.025. The non-isomorphous crystals of the selenium analog are also orthorhombic, Cmca, with a=9.300 (1), b=19.724 (1), c=8.064 (1) A, V=1479.1 (4) A, Z=4, and Dc =2.21 g cm−2. Refinement with 48 variables using 447 observed reflections gives R=0.041. In both structures the molecules have 2/m symmetry imposed by the lattice symmetry; the S (or Se) atoms of the central 4-membered ring are located on the rotation axis, and the P, exo S (or Se), and two carbon atoms of the t-butyl group lie on the mirror plane. The central rings are not readily hydrolyzed or oxidized by exposure to air, apparently as a result of steric protection provided by the t-butyl groups.

The specification generated during the requirements specification phase acts as a cornerstone for the entire software development process. The quality of this document directly influences the overall quality of the resulting software product. The process of requirements specification uses as its input a natural language requirements document, generated by the system's users. This document serves as a guide to the actual specification process. A method is presented for the evaluation and analysis of this document. This analysis permits improvements to be made in the initial requirements document before its use in a formalized specification paradigm. By improving the quality of this document, the input to the specification process is enhanced. This enhancement strengthens not only the developed specification, but also the entire software development process.

Phenothiazine-10-propionitrile, C12H8SNC2H4CN, crystallizes in the centrosymmetric monoclinic space group P21/n, with a = 5.785(1)A, b = 15.427(3)A, c = 14.497(4)A, β = 92.50(1)°, Z = 4, Dmeas = 1.29(1) g cm3 and Dcalc = 1.28 g cm3 at 23°. Three dimensional X-ray data were collected with a manual diffractometer using MoKα (λ 0.71069A) radiation and by multiple film Weissenberg techniques using CuKα (λ 1.5418A) radiation. The structure was determined by Patterson and Fourier methods and refined with 519 observed reflections by full matrix least-squares methods to an R of 0.077. The dihedral angle between the two planes of the o-phenylene rings is 135.4(3)°. In the folded heterocyclic ring the C-S-C angle is 97.8(7)° and the average CS bond is 1.76(1)A. A comparison of this structure to that of phenothiazine-10-propionic acid shows the two chemically similar molecules have the same dihedral angles in spite of completely different solid state packing patterns.

The crystal structure of phenothiazine-10-propionic acid, C12H8SNC2H4COOH, was determined from three-dimensional X-ray diffraction data collected with a manual diffractomer using MoKα (λ 0.71069 A) radiation. The space group is P21/c with a = 7.888 (2)A, b = 8.703 (2)A, c = 19.700 (8)A, β = 101.42 (1)°, Z = 4, Dmeas = 1.35(2) g. cm−3 and Dcalc = 1.36 g. cm−3 at 23°. The structure was determined by the direct method and refined with 500 observed reflections by full-matrix least squares to an R of 0.072. The molecule is folded along the S-N axis and the dihedral angle is 136.5°. The C-S-C angle is 98.5(7)° and the average C-S bond is 1.77(2)A. The shortening of the C-S bond, the small value of the C-S-C angle and the folding of the molecule are typical of the phenothiazine class of compounds and are assumed to be due to sulfur d orbital participation in ring bonding.