77Se NMR Spectra Research Articles

Synthesis and Reactivity of W3Te74+ Clusters and Chalcogen Exchange in the M3Q7 (M = Mo, W; Q = S, Se, Te) Cluster Family

Heating WTe(2), Te, and Br(2) at 390 degrees C followed by extraction with KCN gives [W(3)Te(7)(CN)(6)](2-). Crystal structures of double salts Cs(3.5)K{[W(3)Te(7)(CN)(6)]Br}Br(1.5).4.5H(2)O (1), Cs(2)K(4){[W(3)Te(7)(CN)(6)](2)Cl}Cl.5H(2)O (2), and (Ph(4)P)(3){[W(3)Te(7)(CN)(6)]Br}.H(2)O (3) reveal short Te(2)...X (X = Cl, Br) contacts. Reaction of polymeric Mo(3)Se(7)Br(4) with KNCSe melt gives [Mo(3)Se(7)(CN)(6)](2-). Reactions of polymeric Mo(3)S(7)Br(4) and Mo(3)Te(7)I(4) with KNCSe melt (200-220 degrees C) all give as final product [Mo(3)Se(7)(CN)(6)](2)(-) via intermediate formation of [Mo(3)S(4)Se(3)(CN)(6)](2-)/[Mo(3)SSe(6)(CN)(6)](2-) and of [Mo(3)Te(4)Se(3)(CN)(6)](2-), respectively, as was shown by ESI-MS. (NH(4))(1.5)K(3){[Mo(3)Se(7)(CN)(6)]I}I(1.5).4.5H(2)O (4) was isolated and structurally characterized. Reactions of W(3)Q(7)Br(4) (Q = S, Se) with KNCSe lead to [W(3)Q(4)(CN)(9)](5-). Heating W(3)Te(7)Br(4) in KCNSe melt gives a complicated mixture of W(3)Q(7) and W(3)Q(4) derivatives, as was shown by ESI-MS, from which E(3)[W(3)(mu(3)-Te)(mu-TeSe)(3)(CN)(6)]Br.6H(2)O (5) and K(5)[W(3)(mu(3)-Te)(mu-Se)(3)(CN)(9)] (6) were isolated. X-ray analysis of 5 reveals the presence of a new TeSe(2-) ligand. The complexes were characterized by IR, Raman, electronic, and (77)Se and (125)Te NMR spectra and by ESI mass spectrometry.

Selenium−Tellurium Sequences in Binary Glasses as Depicted by 77Se and 125Te NMR

Some resolved solid state (77)Se NMR spectra are presented in the Te(x)Se(1-x) vitreous system at ambient temperature. They exhibit three different kinds of Se lines assigned to the following Se atom neighborhoods: Se-Se-Se, Se-Se-Te, and Te-Se-Te. Different models were considered to describe the way the Se and Te atoms are linked into the chains: clustering process, homogeneous distribution, random distribution. Finally, thanks to the measurements of the relative intensities of the lines, it appears that Se and Te atoms are mainly randomly distributed with a small preference for heteropolar bonds. The (125)Te spectra are also shown but their resolution is too weak to be informative concerning the vitreous network.

A nonacoordinated bridging selenide in a tricapped trigonal prismatic geometry identified in undecanuclear copper clusters: syntheses, structures, and DFT calculations.

Undecanuclear copper clusters, [Cu(11)(micro(9)-Se)(micro(3)-Br)(3)[Se(2)P(OR)(2)](6)] (R = Et, Pr, (i)Pr) (1a-c), were isolated along with closed-shell ion-centered cubes, [Cu(8)(micro(8)-Br)[Se(2)P(OR)(2)](6)] (PF(6)) (2a-c) and [Cu(8)(micro(8)-Se)[Se(2)P(OR)(2)](6)] (3a-c), from the reaction of [Cu(CH(3)CN)(4)](PF(6)), NH(4)[Se(2)P(OR)(2)], and Bu(4)NBr in a molar ratio of 2:3:2 in CH(2)Br(2). The molecular formulations of these clusters were confirmed by elemental analysis, positive FAB mass spectrometry, and multinuclear NMR ((1)H, (31)P, and (77)Se). (77)Se NMR spectra of Cu(11) clusters (1a-c) are of special interest as two inequivalent selenium nuclei of the diselenophosphate (dsep) ligand exhibit different scalar coupling patterns with the adjacent phosphorus nuclei. X-ray analysis of 1c reveals a Cu(11)Se core stabilized by three bromide and six dsep ligands. The central core adopts the geometry of a 3,3,4,4,4-pentacapped trigonal prism with a selenium atom in the center. The coordination geometry for the nonacoordinate selenium atom is tricapped trigonal prismatic. The X-ray structure 2a or 2c consists of a cationic cluster in which eight copper ions are linked by six diselenophosphate ligands with a central micro(8)-Br ion. The shape of the molecule is a bromide-centered distorted Cu(8) cube. Each diselenophosphate ligand occupies square faces of the cube and adopts a tetrametallic tetraconnective coordination pattern. Each copper atom of the cube is coordinated by three selenium atoms with a strong interaction with the central bromide ion. Molecular orbital calculations at the B3LYP level of the density functional theory have been carried out to study the Cu-micro(9)-Se interactions for clusters [Cu(11)(micro(9)-Se)(micro(3)-X)(3)[Se(2)P(OR)(2)](6)] (X = Br, I). Calculations show that the formal bond order of each Cu-micro(9)-Se bond is slightly smaller than half of those calculated for the terminal Cu-micro(2)-Se bonds.

Highly efficient Peterson olefination leading to unsaturated selenoamides and their characterization.

The Peterson olefination of aromatic aldehydes with an alpha-silyl selenoacetamide proceeded smoothly with high stereoselectivity to give E-alpha,beta-unsaturated selenoamides in good to high yields. The reaction with aldehydes bearing alkenyl and dienyl groups gave the corresponding selenoamides bearing dienyl and trienyl groups, but the stability of the products depended on the substituents on the aromatic ring. X-ray molecular analysis disclosed that the alpha,beta,gamma,delta-unsaturated selenoamides had a nearly planar structure. In the (77)Se NMR spectra, signals were observed in the region greater than 130 ppm depending on the substituents on the aromatic ring, whereas the (1)J coupling constant between the carbon atom and the selenium atom was almost independent of the substituents. A linear relationship was observed between the chemical shifts in the (77)Se NMR spectra and Hammet sigma parameters, and this correlation was retained even when one or two alkenyl groups were introduced to alpha,beta-unsaturated selenoamides, although it became less sensitive.

Efficient chiral discrimination by 77Se NMR.

[reaction: see text] Several (77)Se NMR experiments were performed by titrating a sample of selenides with the chiral shift reagent methylbenzylamine (MBA), followed by acquisition of (77)Se NMR spectra. Eventually, we observed the appearance of two anisochronous resonances, with a relatively large separation, from 37 to 56 Hz, corresponding to the formation of the diastereomeric complexes. This methodology avoids derivatization processes, and the studied compound can be easily recovered from the NMR tube.

Ammonium eneselenolates: stereochemistry and electronic properties.

Ammonium eneselenolates were generated with high efficiency by reacting selenothioic acid S-esters with a THF solution of TBAF. The methylation of ammonium eneselenolates gave ketene selenothioacetals as stereoisomeric mixtures. The ratio of the two stereoisomers depended on the duration of the reaction before the addition of MeI. Ammonium eneselenolates were characterized by examining their (1)H, (13)C, and (77)Se NMR spectra, which indicated that ammonium eneselenolates were present almost exclusively as Z-isomers. These results suggested that ammonium eneselenolates are kinetically generated as stereoisomeric mixtures, and isomerization of E-isomers to Z-isomers then takes place to result in the exclusive formation of Z-isomers. During the methylation of Z-isomers of ammonium eneselenolates, the isomerization of Z-isomers to E-isomers occurs to give stereoisomeric mixtures of ketene selenothioacetals. NMR spectra of ammonium eneselenolates implied that the electrons at the selenium atom are somewhat delocalized to the carbon-carbon double bond and the carbon-selenium bond shows partial double-bond character.

Preparation, crystal structure, and spectroscopic characterization of [(Se(2)SN(2)Cl](2).

The reaction of [(Me(3)Si)(2)N](2)S with an equimolar amount of SeCl(4) in dioxane at 50 degrees C affords [(Se(2)SN(2))Cl](2) (1) in excellent yield. Crystals of 1 are orthorhombic, space group Pbca, with a = 8.5721(7) A, b = 7.8336(6) A, c = 15.228(1) A, and Z = 8. The crystal structure contains two planar Se(2)SN(2)(*)(+) rings which are linked by intermolecular Se.Se interactions [d(Se-Se) = 3.0690(7) A]. The EI mass spectrum shows Se(2)SN(2)(*)(+) as the fragment of highest mass. Both the (14)N and (77)Se NMR spectra show a single resonance (-52 and 1394 ppm, respectively). The solid [(Se(2)SN(2))Cl](2) gives a strong ESR signal indicating the presence of a Se(2)SN(2)(*)(+) radical. The Raman spectrum was assigned through normal coordinate treatment involving a general valence force field. The vibrational analysis yielded a good agreement between the observed and calculated wavenumbers.

NMR in the pseudogap- and charge-density-wave states of (TaSe 4) 2I

We have studied the 77 Se NMR spectrum and spin-lattice relaxation rate (SLRR) in the quasi-one-dimensional conductor (TaSe 4 ) 2 I in the temperature range of 150 to 320 K, i.e., both above and below the temperature of the charge-density wave transition, T c = 263 K. Both the Knight shift and the SLRR vary strongly with temperature in the entire range investigated with no sharp feature at T c . In particular, no critical divergence or Hebel-Slichter peak is observed. The SLRR is strongly non-Korringa, i.e., not proportional to the square of the Knight shift times temperature. All these findings are interpreted in terms of a fluctuating gap model.

Electronic properties of novel donor–acceptor type charge transfer complexes, (BETS) 2(X 2TCNQ) ( X=Cl, Br): 1H, 77Se and 13C-NMR

13 C and 77 Se NMR measurements were performed to investigate the electronic properties of (BETS) 2 (X 2 TCNQ) (X=Cl, Br). The susceptibility was decomposed into the contributions of BETS and X 2 TCNQ site. The line broadening of the 1 H/ 77 Se NMR spectra were observed in the Br 2 TCNQ complex at the metal insulator transition temperature, 12 K. Non magnetic spin singlet formation on the Br 2 TCNQ site was observed at 80 K by 13 C NMR. Line broadening of the 1 H NMR spectra were also observed in the Cl 2 TCNQ complex at the metal insulator transition temperature. The insulating state of the Br and Cl 2 TCNQ complexes under pressure are both magnetic. The holes on the BETS layers are relevant to the magnetic ordering.

Preparation, X-ray Structure, and Spectroscopic Characterization of 1,5-Se2S2N4

The reaction of [(Me(3)Si)(2)N](2)S with equimolar amounts of SCl(2) and SO(2)Cl(2) produces S(4)N(4) in a good yield. The new chalcogen nitride 1,5-Se(2)S(2)N(4) has been prepared in high yield by two different reactions: (a) from [(Me(3)Si)(2)N](2)S and SeCl(4) and (b) from [(Me(3)Si)(2)N](2)Se with equimolar amounts of SCl(2) and SO(2)Cl(2). 1,5-Se(2)S(2)N(4) has a cage structure similar to those of S(4)N(4) and Se(4)N(4). The crystal structure is disordered with site occupation factors ca. 50% for selenium in each chalcogen atom position. The 12 eV EI mass spectrum shows Se(2)SN(2)(+) as the fragment with highest mass. Both the (14)N and (77)Se NMR spectra show a single resonance (-238 and 1418 ppm, respectively). These data rule out the possibility that the crystalline sample is a solid solution of S(4)N(4) and Se(4)N(4) and imply the presence of 1,5-Se(2)S(2)N(4). This deduction was further verified by Raman spectroscopy and vibrational analysis.

Organometallic Selenolates. 5.(1) Synthesis and Complexing Properties of 2-Propene- and 2-Methyl-2-propeneselenolato Molybdenum and Tungsten Compounds. Crystal Structures of cp(CO)(3)WSeCH(2)C(CH(3))=CH(2), [cp(CO)(2)MoSeCH(2)C(CH(3))=CH(2)](2), [cp(CO)(3)Mo(&mgr;-SeCH(2)C(CH(3))=CH(2))W(CO)(5)], [cp(CO)(3)Mo(&mgr;-SeCH(2)C(CH(3))=CH(2))Mo(CO)(5)], and [cp(CO)(3)Mo(&mgr;-SeCH(2)CH=CH(2))Mo(CO)(5)

2-Propene- and 2-methyl-2-propeneselenolato complexes of molybdenum(II) and tungsten(II) have been prepared via insertion of gray selenium into alkali-metal-molybdenum and -tungsten bonds and subsequent reaction with allyl and beta-methallyl chlorides. The complexes are monomeric in the solid state. The (beta-methallyl)molybdenum compound cp(CO)(3)MoSeCH(2)C(CH(3))=CH(2) (2) decomposes slowly in solution with CO loss and formation of the corresponding dimer [cp(CO)(2)MoSeCH(2)C(CH(3))=CH(2)](2) (3), whose crystal structure has been determined (C(22)H(24)Mo(2)O(4)Se(2), monoclinic, P2(1)/c, a = 11.151(2) Å, b = 13.436(3) Å, c = 16.872(3) Å, beta = 102.42(2) degrees, Z = 4). A monomeric structure has been found for cp(CO)(3)WSeCH(2)C(CH(3))=CH(2) (5) (C(12)H(12)O(3)SeW, triclinic, P&onemacr;, a = 7.592(3) Å, b = 7.700(3) Å, c = 12.296(5) Å, alpha = 98.31(4) degrees, beta = 104.24(2) degrees, gamma = 108.49(3) degrees, Z = 2). Additionally, the complexing properties of the selenolato complexes have been investigated. The reactions of the molybdenum complexes cp(CO)(3)MoSeCH(2)CH=CH(2) (1) and (2) with the metal(0)-carbonyl complexes W(CO)(5)(THF), (CH(3)CN)(3)Mo(CO)(3), and (eta(6)-C(7)H(8))Mo(CO)(3) (C(7)H(8) = cycloheptatriene) led to the formation of [cp(CO)(3)Mo(&mgr;-SeCH(2)C(CH(3))=CH(2))M(CO)(5)] (M = W (6), Mo (7)) and [cp(CO)(3)Mo(&mgr;-SeCH(2)CH=CH(2))Mo(CO)(5)] (8), respectively. 6 and 7 are isostructural and crystallize in the monoclinic space group P2(1)/n (6, C(17)H(12)MoO(8)SeW, a = 14.708(2) Å, b = 9.837(2) Å, c = 14.958(2) Å, beta = 103.030(10) degrees, Z = 4; 7, C(17)H(12)Mo(2)O(8)Se, a = 14.712(2) Å, b = 9.8670(10) Å, c = 14.982(2) Å, beta = 103.100(10) degrees, Z = 4), whereas [cp(CO)(3)Mo(&mgr;-SeCH(2)CH=CH(2))Mo(CO)(5)] (8) crystallizes in the noncentrosymmetric orthorhombic space group Pna2(1) (C(16)H(10)Mo(2)O(8)Se, a = 18.638(4) Å, b = 9.707(2) Å, c = 11.169(3) Å, Z = 4). Furthermore, (77)Se-NMR spectra displayed chemical shifts consistent with earlier results on related complexes.

Preparation and phosphorus-31 and selenium-77 NMR spectra of platinum and palladium complexes of a P2N4Se2 ring

The reaction of 1,5-Ph 4 P 2 N 4 Se 2 with Pt(PPh 3 ) 2 (CH 2 =CH 2 ) or Pd(PPh 3 ) 4 in toluene at 0 o C produces the η 2 -Se,Se'-bonded complexes M(PPh 3 ) 2 (1,5-Ph 4 P 2 N 4 Se 2 ) (2a, M=Pt; 2b, M=Pd) characterized by their 31 P and 77 Se NMR spectra. Simulation of the 77 Se NMR spectra gave detailed coupling information for 2a and 2b.

Conformational analysis of benzoannulated nine-membered rings. Part3. 1,4,5,7-Tetrahydro-3H-2,6-benzodiselenine and its 4-spiro derivatives

The 1 H and 13 C nmr spectra of 1,4,5,7-tetrahydro-3H-2,6-benzodiselenine (1) and three 4-spiro derivatives 2-4 as well as the 77 Se nmr spectra of 2 have been recorded at different temperatures in order to investigate their conformational behavior. It was found that in analogy to corresponding dithionins the molecules adopt a chiral ground state conformation (Figure 2), and coalescence effects are due to racemization

Evidence for the Slow Motion of Organic Molecules in (TMTSF)2ClO4Extracted from the Spin Echo Decay of77Se NMR

The 77 Se nuclear spin echo decay rate (1/ T 2 ) in the organic conductor (TMTSF) 2 ClO 2 was found to exhibit a large peak around 30∼32 K, slightly above the structural phase transition temperature T t =24 K. The peak was more pronounced with increasing field. This result indicates that the slow motion of TMTSF, molecules with large amplitude, most probably associated with change in the molecular orientation, develops above T t , which gives rise to spin echo decay via. the fluctuations of the anisotropic Knight shift. From the analysis of the spin echo decay, it is found that the amplitude of this motion reaches maximum at 30∼32 K and its correlation time is estimated to be 10 3 ∼10 -5 sec depending on temperature. A change was found also in the 77 Se NMR spectrum in this temperature region which may be interpreted as the motional narrowing effect.