Weak Se Research Articles

A New Building Block for Organometallic–Inorganic Hybrid Polymers: The Mixed Group 15/16 Element Ligand Complex [Cp*2Mo2(μ,η2:2‐PSe)2(μ‐Se)] (Cp* = C5Me5)

AbstractThe synthesis and spectroscopic characterization of [Cp*2Mo2P2Se3] (1; Cp* = C5Me5) and its use as a molecular building block in the formation of copper(I) halide polymers is described. The reaction of 1 in CH2Cl2 with 2 equiv. of CuBr and CuI in CH3CN under diffusion conditions gave [(Cp*2Mo2P2Se3)2(CuBr)2] (2) and [(Cp*2Mo2P2Se3)(CuX)3(CH3CN)]n (X = I; 3/4), respectively. The structure of 2 is distinguished by a central Cu2Br2 ring coordinated on each side by a tripledecker complex through one of its P atoms. A 2D network is formed by weak interactions between Se atoms of neighboring molecules. Compound [(Cp*2Mo2P2Se3)(CuI)3(CH3CN)]n exists in two isomeric forms 3 and 4. The crystal structure of 3 can be described as a two‐dimensional polymer that is formed by ribbons containing looped chains of three Cu2I2 rings and attached [Cp*2Mo2P2Se3] molecules. The structure of 4 contains a ribbon in which tripledecker molecules are linked through their P atoms to (CuI)6 clusters. The ribbons are connected by weak Se···Se interactions. The reaction of a mixture of 1 and P4Se3 with CuI gave [(Cp*2Mo2P2Se3)(P4Se3)(CuI)2]n. The crystal structure analysis of 5 reveals a new type of organometallic–inorganic framework in which 1 and P4Se3 are linked by Cu2I2 rings.

Silver(I), Copper(I) and Copper(II) Complex of the New N,Se‐Chelate Ligand 2‐Phenylselenomethyl‐1H‐benzimidazole: Electrochemistry and Structure

Abstract2‐Phenylselenomethyl‐1H‐benzimidazole (psbi) can form complexes in 2:1 ratio with coinage metal ions. Crystal structure analysis revealed a flattened metal coordination for [AgI(psbi)2](BF4) (1), approaching a distorted‐planar arrangement with weak Ag–Se bonds (d > 2.9 Å) and confirmed as energy minimum by DFT calculations. The typical Jahn–Teller system [CuII(psbi)2Cl2] (2) exhibits a planar CuN2Cl2 core with weak Se···Cu···Se axial ligation [3.2944(8) Å Cu···Se distance]. The oxygen‐sensitive compound [CuI(psbi)2](BF4) (3) exhibits electrochemically reversible oxidation in contrast to the silver(I) analogue 1.

Flexible Polar Nanowires of Cs5BiP4Se12 from Weak Interactions between Coordination Complexes: Strong Nonlinear Optical Second Harmonic Generation

The Cs(5)BiP(4)Se(12) salt grows naturally as nanowires that crystallize in the polar space group Pmc2(1), with a = 7.5357(2) A, b = 13.7783(6) A, c = 28.0807(8) A, and Z = 4 at 293(2) K. The compound features octahedral [Bi(P(2)Se(6))(2)](5-) coordination complexes that stack via weak intermolecular Se...Se interactions to form long, flexible fibers and nanowires. The Cs(5)BiP(4)Se(12) fibers are transparent in the near- and mid-IR ranges and were found to exhibit a nonlinear optical second harmonic generation response at 1 microm that is approximately twice that of the benchmark material AgGaSe(2). The material has a nearly direct band gap of 1.85 eV and melts congruently at 590 degrees C. Ab initio electronic structure calculations performed with the full-potential linearized augmented plane wave (FLAPW) method show that the band gap increases from its local density approximation (LDA) spin-orbit coupling value of 1.15 eV to the higher value of 2.0 eV when the screened-exchange LDA method is invoked and explain how the long nanowire nature of Cs(5)BiP(4)Se(12) emerges.

Soft–Soft Interactions Involving Iodoselenophosphonium Cations: Supramolecular Structures of Iodine Adducts of Bulky Trialkylphosphane Selenides

AbstractThe reactions of trialkylphosphane selenides tBuniPr3–nPSe (n = 3: 1a; n = 2: 1b; n = 1: 1c; n = 0: 1d) with iodine are studied with the help of heteronuclear NMR spectroscopy, vibrational spectroscopy, and X‐ray crystal structure determinations. The reaction of 1a with one equivalent of iodine provides, after crystallization from dichloromethane/pentane, solid 2a, which consists of pairs of molecular adducts tBu3PSe–I–I, together with chains of alternating [(tBu3PSe)2I]+ and I3– ions. The addition of iodine to 1b, 1c, and 1d in a 1:1 molar ratio furnishes ionic solids with the formulation [(tBuniPr3–nPSe)2I]+[I3]– (n = 2: 2b; n = 1: 2c; n = 0: 2d). Compounds 2a–2d exhibit supramolecular structures based on various kinds of weak Se···I and Se···Se interactions. In 2a, the uncharged molecules form dimers through Se···Se contacts, while the anions and cations assemble to form chains through linear P–Se···Ianion contacts. The ionic compounds 2b and 2d consist of the same type of chains, although they are not isotypic to each other. The two independent formula units of 2c are topologically different; one forms cation–anion chains analogous to those of 2b and 2d, whereas the other forms cation chains through Se···Se contacts. Se···I contacts between the latter chains and triiodide anions are very long but seem to be structurally significant; for such contacts, at well above the sum of the van der Waals radii, we propose the term tertiary contacts. On using more than one equivalent of I2, compounds corresponding to the formulation tBuniPr3–nPSeIx (x = 3, n = 3: 3a; x = 4, n = 1: 4c; x = 7, n = 2 and 0: 5b and 5d) were isolated as single crystals. Ionic 3a contains pairs of cations [(tBu3PSe)2I]+, connected by Se···Se contacts, located between corrugated layers of polymeric I5– anions. Compound 4c consists of two independent formula units tBuiPr2PSeI2·I2, which could, however, be regarded as tBuiPr2PSeI+·I–·I2 because of the long I–I distance adjacent to Se. To a fair approximation, the packing of the two units is independent; unit 1 forms dimers (···Se–I–I···I–I···)2, whereas the same motif in unit 2 forms chains. The structural subunits are linked through further contacts involving terminal iodine atoms from tBuiPr2PSeI···I units, which thereby form μ3‐bridging units, and by additional I–I···Se contacts. In 5b,iodide‐bridged cations [tBu2iPrPSeI···I···ISePiPrtBu2]+ are anchored to a polyiodide network of formal composition I11–[= (I–)(I2)5] through I···I contacts. Except for one I···I contact, the polyiodide is two‐dimensional, although highly puckered. In 5d, [iPr3PSeI]+ cations and I2 molecules exhibit weak I···I interactions with I– units from puckered square‐net‐like polyiodide layers. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Dinuclear Manganese(II) Complexes with Bridging Selenidodiarsenate Anions [As2Se4]4−, [As2Se5]4− and [As2Se6]2−

AbstractSolvothermal reaction of [MnCl2(amine)] (amine = terpy and tren) with elemental As and Se at a 1:1:2 molar ratio in H2O/tren (10:1) affords the dimanganese(II) complexes [{Mn(terpy)}2(μ‐As2Se4)] (1) and [{Mn(tren)}2(μ‐As2Se5)] (2) respectively. The tetradentate [As2Se4]4− bridging ligands in 1 contain a central As–As bond and exhibit approximately C2h symmetry. Pairs of gauche sited Se atoms participate in five‐membered As2Se2Mn chelate rings. In contrast, two AsSe3 pyramids share a common corner in the [As2Se5]4− ligands of 2 and each coordinates an [Mn(tren)]2+ fragment through a single terminal Se atom. Such dinuclear complexes are linked into tetranuclear moieties through weak Se···Mn interactions of length 3.026(3) Å involving one of these terminal Se atoms. At a 1:3:6 molar ratio, solvothermal reaction of [MnCl2(tren)] with As and Se leads to formation of a second dinuclear complex [{Mn(tren)}2(μ‐As2Se6)2] (3), which contains two bridging bidentate [As2Se6]2− ligands. These are cyclic with an As2Se4 ring and can be regarded as being derived from [As2Se5]4− anions by formation of two Se‐Se bonds to an additional Se atom.

Synthesen und Kristallstrukturen neuer chalkogenido-verbrückter Niob-Kupfer-Cluster

Syntheses and Crystal Structures of Novel Chalcogenido-bridged Niobium Copper Clusters In the presence of tertiary phosphines, the reaction of NbCl5 and Copper(I) salts with Se(SiMe3)2 (E = S, Se) affords the new chalcogenido-bridged niobium-copper cluster compounds (1) and [NbCu4Se4Cl (PPh3)4] (2). Using E(R)SiMe3 (E = S, Se, R = Ph, nPr) instead of the bisilylated selenium species leads to the compounds [NbCu2(SPh)6(PMe3)2] (3), [NbCu2(SPh)6(PnPr3)2] (4), [NbCu2(SePh)6(PMe3)2] (5), [NbCu2(SePh)6(PnPr3)2] (6), [NbCu2(SePh)6(PiPr3)2] (7), [NbCu2(SePh)6(PtBu3)2] (8), [NbCu2(SePh)6(PiPr2Me)2] (9), [NbCu2(SePh)6(PPhEt2)2] (10), [Nb2Cu2(SnPr)8(PnPr3)2Cl2] (11) and [Nb2Cu6(SnPr)12(PiPr3)2Cl4]·2 CH3CN (12·2 CH3CN). By reacting CuI salts and NbCl5 with the monosilylated selenides Se(tBu)SiMe3 and Se(iPr)SiMe3 which have a weak Se–C bond the products [Nb2Cu6Se6(PiPr3)6Cl4] (13), [Nb2Cu4Se2(SeiPr)6(PnPr3)4Cl2] (14) and [Nb2Cu6Se2(SeiPr)10(PEt2Me)2Cl2]·DME (15) are formed which contain selenide as well as alkylselenolate ligands. The molecular structures of all of these new compounds were determined by single crystal X-ray diffraction measurements.

A comparison of the solid-state structures of a series of phenylseleno-halogen and pseudohalogen compounds, PhSeX (X = Cl, CN, SCN)

Structural and spectroscopic data on the series of compounds “PhSeX”, where X = Cl, CN or SCN, are reported and compared with previously reported data on “PhSeX” systems (X = Br and I). The chloro-compound displays a “square” motif, Ph 4Se 4Cl 4, in the solid state, linked by long Se–Se bonds [2.993(3)–3.035(3) Å], and forms a loosely held network of Se 4 and Cl 4 squares in its extended structure. In contrast, the pseudohalogen derivatives, PhSeCN and PhSeSCN, consist of essentially monomeric units, which form chains held together by weak Se⋯N interactions in the solid state. These Se⋯N interactions are much shorter in PhSeCN, 3.023(3)–3.065(4) Å, than in PhSeSCN, 3.348(4) Å. Weaker Se⋯N contacts are also present between the chains. The structure of PhSeSCN described here is the first reported crystallographic study of a selenium thiocyanate compound. Spectroscopic studies suggest that all three compounds exist as monomers in solution. The results reported herein illustrate the subtle differences in the solid-state structures of PhSeX compounds.

Selenium-Centered, Undecanuclear Silver Cages Surrounded by Iodo and Dialkyldiselenophosphato Ligands. Syntheses, Structures, and Photophysical Properties

Three clusters [Ag11(mu9-Se)(mu3-I)3{Se2P(OR)2}6] (R = Et, 1; iPr, 2; 2Bu, 3) were isolated from the reaction of [Ag(CH3CN)4](PF6), NH4[Se2P(OR)2], and Bu4NI in a molar ratio of 4:3:1 in CH2Cl2 in 47-55% yield. Compounds 1 and 2 can also be synthesized with high yield from the reaction of Ag10(Se)[Se2P(OR)2]8 with 8 equiv of Bu4NI. In the positive fast atom bombardment mass spectra of 1-3, two major peaks that correspond to the intact molecule with the loss of an iodide ion, [Ag11(mu9-Se)(mu3-I)(2){Se2P(OR)2}6]+, and a diselenophosphate ligand, [Ag11(mu9-Se)(mu3-I)3{Se2P(OR)2}5]+, were identified. Single-crystal X-ray analyses of 2 and 3 reveal an Ag11Se core stabilized by three iodide anions and six diselenophosphato ligands in a tetrametallic tetraconnective (mu2,mu2) coordination mode. The central core adopts the geometry of a 3,3,4,4,4-pentacapped trigonal prism with a selenium atom in the center. In addition, weak intermolecular Se...I interactions exist in 2 and form a one-dimensional polymeric chain structure. Furthermore, all compounds exhibit orange-red luminescence in both the solid state and solution.

Experimental and Theoretical Studies on the Nature of Weak Nonbonded Interactions between Divalent Selenium and Halogen Atoms

To investigate the nature of weak nonbonded selenium...halogen interactions (Se...X interactions; X = F, Cl, and Br), three types of model compounds [2-(CH(2)X)C(6)H(4)SeY (1-3), 3-(CH(2)X)-2-C(10)H(6)SeY (4-6), and 2-XC(6)H(4)CH(2)SeY (7-9); Y = CN, Cl, Br, SeAr, and Me] were synthesized, and their (77)Se NMR spectroscopic behaviors were analyzed in CDCl(3). The gradual upfield shifts of (77)Se NMR absorptions observed for series 1-3 and 4-6 suggested that the strength of Se...X interaction decreases in the order of Se...F > Se...Cl > Se...Br. The quantum chemical calculations at the B3LYP/631H level using the polarizable continuum model (PCM) revealed that the most stable conformer for 1-3 is the one with an intramolecular short Se...X atomic contact in CHCl(3) (epsilon = 4.9) and also that the n(X) --> sigma(Se-Y) orbital interaction (E(Se...X)) can reasonably explain the order of strength for the Se...X interactions. On the other hand, the (77)Se NMR absorptions observed for series 7-9 did not shift significantly from the reference compounds (C(6)H(5)CH(2)SeY), indicating the absence of the Se...X interaction for 7-9 presumably due to attenuation of basicity for the halogen atom that is substituted directly to the aromatic ring. These observations suggested that the n(X) --> sigma(Se-Y) orbital interaction is a dominant factor for formation of weak Se...X interactions. Electron correlation was also suggested to be important for the stability.

Intermolecular Se⋯Se interactions observed in indium compounds containing dialkyl diselenophosphate ligands: syntheses, structure, and solution studies of [In{Se 2P(OR) 2} 3] (R = Et, iPr)

Weak intermolecular Se⋯Se interactions exist between adjacent molecules of [In{Se 2P(O i Pr) 2} 3] and form a loosely connected dimer. VT 31P NMR studies suggest that In–Se bonds are labile in solution.

Cu(I) and Ag(I) complexes of chalcogenide derivatives of the organometallic ligand dppf and the dppa analogue

New Cu(I) and Ag(I) complexes were prepared by reaction of [M(NCCH 3) 4][X] (M = Cu or Ag; X = BF 4 or PF 6) with the bidentate chalcogenide ligands Ph 2P(E)NHP(E)Ph 2 (E = S, S 2dppa; E = Se, Se 2dppa), and dpspf (1,1′-bis(diphenylselenophosphoryl)ferrocene). Copper and silver behaved differently. While three molecules of either S 2dppa and Se 2dppa bind to a distorted tetrahedral Cu 4 cluster, with deprotonation of the ligand, 1:2 complexes of the neutral ligands are formed with Ag(I), with a tetrahedral coordination of the metal. The [Cu 4{Ph 2P(Se)NP(Se)Ph 2} 3] + clusters assemble as dimers, held together by weak Se⋯Se distances interactions. Another dimer was observed for the [Ag(dpspf)] + cation, with two short Ag⋯Se distances. DFT and MP2 calculations indicated the presence of attracting interactions, reflected in positive Mayer indices (MI). The electrochemistry study of this species showed that both oxidation and reduction took place at silver.

The Reaction of Selenium Trioxide with Dialkyl Ethers

AbstractThe donor‐acceptor complexes Et2O·SeO3 and (Me2O)2·SeO3 can be obtained as primary products by the reactions of selenium trioxide with dimethyl ether (Me2O) and diethyl ether (Et2O). The crystal and molecular structure of both complexes, which are stable below their melting points only, was determined by X‐ray structure analysis. Pairs of molecules Et2O·SeO3 form dimers due to two weak intermolecular Se···O contacts. No intermolecular interactions were observed in (Me2O)2·SeO3. Trigonal bipyramidal coordination around SeVI atoms in the latter complex is almost undistorted. Conversion of the adducts to dialkylesters of diselenic and selenic acid in the liquid phase was monitored by Raman, 1H‐ and 77Se‐NMR spectroscopy.

9.2.5 A Tale of Two Systems – A Comparative Study of Systems Engineering

AbstractThis paper is a comparative study of two system development projects as a contribution to the demand for evidence of the benefits of Systems Engineering.The treatment is qualitative, but the similarities of the two systems concerned allow useful conclusions to be drawn. The projects were carried out by the same enterprise, used common subcontractors, were developed on similar technical infrastructure and were developed for the same end user. Both projects claimed to be applying Systems Engineering, however the very different outcomes conform to the old adage that says, ‘it ain't what you do, it's the way that you do it – that's what gets results‘,Both projects experienced the usual trials and tribulations that accompany engineering developments, however one system was accepted and delivered whilst the other ran significantly over‐budget and over time. This system was never delivered. The seeds of the problems that afflicted the unsuccessful project could be observed very early in the programme, and had they been addressed the outcome could have been different. The paper helps to support the hypothesis that intelligent use of SE can ensure project success.Projects may claim to use SE without actually delivering a good result. The paper addresses this problem by indicating some common sense observations that can identify weak or ineffectual SE practices.Not surprisingly the identity of the projects is not revealed, and in some cases details have been deliberately altered to ensure anonymity.

Quantitative evaluation of weak nonbonded Se...F interactions and their remarkable nature as orbital interactions.

To evaluate weak intramolecular nonbonded Se...F interactions recently characterized for a series of o-selenobenzyl fluoride derivatives (Iwaoka et al., Chem. Lett. 1998, 969-970), the temperature dependence of the nuclear spin coupling between Se and F (J(Se...F)) was investigated for 2-(fluoromethyl)phenylselenenyl cyanate (1a) and bis[2-(fluoromethyl)phenyl] diselenide (1e) in CD2Cl2 and CD3CN. A significant increase in the magnitude of J(Se...F) was observed for both 1a and 1e upon lowering temperature, whereas the values of J(Se...F) for the corresponding trifluoromethyl compounds slightly reduced or remained unchanged at low temperatures. Application of the rapid equilibrium model between two possible conformers revealed that conformer A with an intramolecular Se...F interaction is more stable in enthalpy (DeltaH) by 1.23 kcal/mol for 1a (in CD2Cl2) and by 0.85 and 0.83 kcal/mol for 1e (in CD2Cl2 and CD3CN, respectively) than conformer B, which does not have close Se...F contact. The negligible solvent effects for 1e suggested marginal electrostatic nature of the Se...F interactions. Instead, importance of the n(F) -->sigma*(Se-X) orbital interaction was suggested by quantum chemical (QC) calculations and the natural bond orbital (NBO) analysis.

Syntheses and Structures of Donor-Acceptor Complexes of Selenium Dioxide with Pyridine and Trimethylamine

Donor-acceptor (DA) complexes of pyridine (py)·SeO2 and trimethylamine (TMA)·SeO2 were prepared by direct reactions of solid selenium dioxide with the amines. Both are white solids decomposing slowly at room temperature. The former complex decomposes into its components, while the latter one undergoes a redox reaction. The single-crystal structure determination of py·SeO2 has revealed that the chain-like structure of (SeO2)n is destroyed during the formation of the DA bond and the py·SeO2 molecule is bound to the nearest neighbouring molecule through two weak Se···O interactions. More labile TMA·SeO2 complex could not be prepared as single crystals. Analogous molecular structure of both complexes was proved by their Raman spectra. A modified general valence force field was used for the interpretation of Raman spectra of TMA·SeO2 and TMA·SO2.

Syntheses of THF Solutions of SeX2 (X = Cl, Br) and a New Route to Selenium Sulfides SenS8-n (n = 1−5): X-ray Crystal Structures of SeCl2(tht)2 and SeCl2·tmtu

A simple and efficient synthesis of solutions of pure SeCl2 in THF or dioxane (ca. 0.4 M) at 23 °C was achieved by treatment of elemental selenium with an equimolar amount of SO2Cl2. SeCl2 was characterized by 77Se NMR and Raman spectra. SeCl2 forms 1:1 or 1:2 adducts with tetramethylthiourea (tmtu) or tetrahydrothiophene (tht), respectively. The crystal structure of SeCl2·tmtu (1) reveals a T-shaped geometry [d(Se−Cl) = 2.443(4) Å] with weak intramolecular Se···Cl interactions [d(Se−Cl) = 3.276(4) Å]. Crystals of 1 are triclinic, space group P1̄, with a = 8.473(3) Å, b = 9.236(3) Å, c = 7.709(4) Å, α = 109.90(3)°, β = 92.26(4)°, γ = 107.89(3)°, V = 532.9(4) Å3, and Z = 2. The complex SeCl2(tht)2 (2) adopts a square planar geometry with d(Se−Cl) = 2.4149(8) Å. Crystals of 2 are monoclinic, space group C2/c, with a = 15.6784(8) Å, b = 9.1678(4) Å, c = 9.1246(4) Å, β = 110.892(2)°, V = 1225.3(1) Å,3 and Z = 4. The reaction of Ph3PS with SeCl2 gives Ph3PCl2 and a complex mixture of selenium sulfides SenS8-n (n = 1−5), which were identified by 77Se NMR. Halogen exchange between SeCl2 and Me3SiBr in THF yields thermally unstable SeBr2 (ca. 0.4 M) characterized by 77Se NMR and Raman spectra.

Cleavage Planes in CuInSe2

All angles between facets in CuInSe 2 Bridgman-grown crystals were measured and confirmed, by X-ray Laue patterns and diffractometry, to be accounted for by three planes: {101}, {112} and {110}. The {110} facets were less frequent and were found to consist of {112} microcleavages. The {101} cleavages occurred most frequently and it is speculated that this is due to the smaller energy required to break a smaller number of the stronger Se–Cu bonds (compared with the weaker Se–In bonds) than for {112} cleavages.

Oxidative Spaltung von Poly(o1‐phenylendiselenid)

Oxidative Cleavage of Poly(o1‐phenylenediselenide)Poly(o1‐phenylenediselenide) is cleaved at the Se–Se bond by treatment with SOCl2 to give benzene‐1,2‐bis(selenenyl chloride) (2) and benzene‐1,2‐bis(selenium trichloride) (3), respectively. In the solid state 2 is dimerized by Se…Se bonds whereas 3 is monomeric having terminal as well as intramolecular bridging Cl atoms. Treatment of 2 with SbCl5 gives an ionic compound (4) with a dimeric cation exhibiting a weak SeSe bond and SbCl6– as a counterion 3 reacts with W(CO)6 to give trigonal prismatic dicarbonyl bis(o1‐phenylenediselenolato)tungsten (5).

Reflex inhibition and reflex strength

In Experiment 1, the amplitude of the acoustic startle reflex in rats was shown to increase linearly with increases in the intensity of the eliciting stimulus (Se). A preliminary stimulus (Si), a light flash, inhibited the reflex. The amplitude of the reflex was reduced by an equal amount regardless of Se intensity. In Experiment 2, the amplitude of the same reflex was shown to have a biphasic relation to the intensity of a white noise background (Sn) and reflex amplitudes peaked at the intermediate noise levels. Although the vigor of the reflex elicited in the presence of the most intense noise approximated that elicited by the weak Se in Experiment 1, in this condition the reflex was unaffected by the occurrence of the otherwise inhibitory light flash. It has been previously hypothesized that the decrement in reflex vigor obtained at high Sn results because sensory masking of Se by Sn reduces the effective intensity of Se. The different effect of Si in these two conditions suggests that this hypothesis is incorrect. A hypothetical neural model was devised to account for the difference between the two reflexes in their susceptibility to a preliminary stimulus, and the model was extended to other effects of stimulus strength and background noise on reflexive behavior.