77Se NMR spectroscopic, DFT MO, and VBT investigations of the reversible dissociation of solid (Se6I2)[AsF6]2.2SO2 in Liquid SO2 to solutions containing 1,4-Se6I2(2+) in equilibrium with Se(n)2+ (n = 4, 8, 10) and seven binary selenium iodine cations: preliminary evidence for 1,1,4,4-Se4Br4(2+) and cyclo-Se7Br+.

The composition of a complex equilibrium mixture formed upon dissolution of (Se(6)I(2))[AsF(6)](2).2SO(2) in SO(2)(l) was studied by (77)Se NMR spectroscopy at -70 degrees C with both natural-abundance and enriched (77)Se-isotope samples (enrichment 92%). Both the natural-abundance and enriched NMR spectra showed the presence of previously known cations 1,4-Se(6)I(2)(2+), SeI(3)(+), 1,1,4,4-Se(4)I(4)(2+), Se(10)(2+), Se(8)(2+), and Se(4)(2+). The structure and bonding in 1,4-Se(6)I(2)(2+) and 1,1,4,4-Se(4)I(4)(2+) were explored using DFT calculations. It was shown that the observed Se-Se bond alternation and presence of thermodynamically stable 4ppi-4ppi Se-Se and 4ppi-5ppi Se-I bonds arise from positive charge delocalization from the formally positively charged tricoordinate Se(+). The (77)Se chemical shifts for cations were calculated using the relativistic zeroth-order regular approximation (ZORA). In addition, calculations adding a small number of explicit solvent molecules and an implicit conductor-like screening model were conducted to include the effect that solvent has on the chemical shifts. The calculations yielded reasonable agreement with experimental chemical shifts, and inclusion of solvent effects was shown to improve the agreement over vacuum values. The (77)Se NMR spectrum of the equilibrium solution showed 22 additional resonances. These were assigned on the basis of (77)Se-(77)Se correlation spectroscopy, selective irradiation experiments, and spectral simulation. By combining this information with the trends in the chemical shifts, with iodine, selenium, and charge balances, as well as with ZORA chemical shift predictions, these resonances were assigned to acyclic 1,1,2-Se(2)I(3)(+), 1,1,6,6-Se(6)I(4)(2+), and 1,1,6-Se(6)I(3)(+), as well as to cyclic Se(7)I(+) and (4-Se(7)I)(2)I(3+). A preliminary natural-abundance (77)Se NMR study of the soluble products of the reaction of (Se(4))[AsF(6)](2) and bromine in liquid SO(2) included resonances attributable to 1,1,4,4-Se(4)Br(4)(2+)(.) These assignments are supported by the agreement of the observed and calculated (77)Se chemical shifts. Resonances attributable to cyclic Se(7)Br(+) were also observed. The thermal stability of (Se(6)I(2))[AsF(6)](2).2SO(2)(s) was consistent with estimates of thermodynamic values obtained using volume-based thermodynamics (VBT) and the first application of the thermodynamic solvate difference rule for nonaqueous solvates. (Se(6)I(2))[AsF(6)](2).2SO(2)(s) is the first example of a SO(2) solvate for which the nonsolvated parent salt, (Se(6)I(2))[AsF(6)](2)(s), is not thermodynamically stable, disproportionating to Se(4)I(4)(AsF(6))(2)(s) and Se(8)(AsF(6))(2)(s) (DeltaG degrees for the disproportion reaction is estimated to be -17 +/- 15 kJ mol(-1) at 298 K from VBT theory).

1,1,4,4-Tetra-methyl-piperazinediium dibromide.

A small quantity of the title compound, C(8)H(20)N(2) (2+)·2Br(-), was formed as a by-product in a reaction between a diamine and an alkyl bromide. The asymmetric unit contains half of a centrosymmetric dication and a bromide anion. In the crystal, weak inter-molecular C-H⋯Br hydrogen bonds consolidate the crystal packing.

N,N-Dimethyl-N-propyl-propan-1-aminium chloride monohydrate.

The title compound, C(8)H(20)N(+)·Cl(-)·H(2)O, has been prepared by a simple one-pot synthesis route followed by anion exchange using resin. In the crystal structure, the cations are packed in such a way that channels exist parallel to the b axis. These channels are filled by the anions and water mol-ecules, which inter-act via O-H⋯Cl hydrogen bonds [O⋯Cl = 3.285 (3) and 3.239 (3) Å] to form helical chains. The cations are involved in weak inter-molecular C-H⋯Cl and C-H⋯O hydrogen bonds. The title compound is not isomorphous with the bromo or iodo analogues.

Accounting for the differences in the structures and relative energies of the highly homoatomic np pi-np pi (n > or = 3)-bonded S2I4 2+, the Se-I pi-bonded Se2I4 2+, and their higher-energy isomers by AIM, MO, NBO, and VB methodologies.

The bonding in the highly homoatomic np pi-np pi (n > or = 3)-bonded S2I42+ (three sigma + two pi bonds), the Se-I pi-bonded Se2I42+ (four sigma + one pi bonds), and their higher-energy isomers have been studied using modern DFT and ab initio calculations and theoretical analysis methods: atoms in molecules (AIM), molecular orbital (MO), natural bond orbital (NBO), and valence bond (VB) analyses, giving their relative energies, theoretical bond orders, and atomic charges. The aim of this work was to seek theory-based answers to four main questions: (1) Are the previously proposed simple pi*-pi* bonding models valid for S2I42+ and Se2I42+? (2) What accounts for the difference in the structures of S2I42+ and Se2I42+? (3) Why are the classically bonded isolobal P2I4 and As2I4 structures not adopted? (4) Is the high experimentally observed S-S bond order supported by theoretical bond orders, and how does it relate to high bond orders between other heavier main group elements? The AIM analysis confirmed the high bond orders and established that the weak bonds observed in S2I42+ and Se2I42+ are real and the bonding in these cations is covalent in nature. The full MO analysis confirmed that S2I42+ contains three sigma and two pi bonds, that the positive charge is essentially equally distributed over all atoms, that the bonding between S2 and two I2+ units in S2I42+ is best described by two mutually perpendicular 4c2e pi*-pi* bonds, and that in Se2I42+, two SeI2+ moieties are joined by a 6c2e pi*-pi* bond, both in agreement with previously suggested models. The VB treatment provided a complementary approach to MO analysis and provided insight how the formation of the weak bonds affects the other bonds. The NBO analysis and the calculated AIM charges showed that the minimization of the electrostatic repulsion between EI2+ units (E = S, Se) and the delocalization of the positive charge are the main factors that explain why the nonclassical structures are favored for S2I42+ and Se2I42+. The difference in the structures of S2I42+ and Se2I42+ is related to the high strength of the S-S pi bond compared to the weak S-I sigma bond and the additional stabilization from increased delocalization of positive charge in the structure of S2I42+ compared to the structure of Se2I42+. The investigation of the E2X42+ series (E = S, Se, Te; X = Cl, Br, I) revealed that only S2I42+ adopts the highly np pi-np pi (n > or = 3)-bonded structure, while all other dications favor the pi-bonded Se2I42+ structure. Theoretical bond order calculations for S2I42+ confirm the previously presented experimentally based bond orders for S-S (2.1-2.3) and I-I (1.3-1.5) bonds. The S-S bond is determined to have the highest reported S-S bond order in an isolated compound and has a bond order that is either similar to or slightly less than the Si-Si bond order in the proposed triply bonded [(Me3Si)2CH]2(iPr)SiSi triple bond SiSi(iPr)[CH(SiMe3)2]2 depending on the definition of bond orders used.

A computational and experimental study of the structures and Raman and 77Se NMR spectra of SeX3+ and SeX2 (X = Cl, Br, I): FT-Raman spectrum of (SeI3)[AsF6].

The ability of MP2, B3PW91 and PBE0 methods to produce reliable predictions in structural and spectroscopic properties of small selenium-halogen molecules and cations has been demonstrated by using 6-311G(d) and cc-pVTZ basis sets. Optimized structures and vibrational frequencies agree closely with the experimental information, where available. Raman intensities are also well reproduced at all levels of theory. Calculated GIAO isotropic shielding tensors yield a reasonable linear correlation with the experimental chemical shift data at each level of theory. The largest deviations between calculated and experimental chemical shifts are found for selenium-iodine species. The agreement between observed and calculated chemical shifts for selenium-iodine species can be improved by inclusion of relativistic effects using the ZORA method. The best results are achieved by adding spin-orbit correction terms from ZORA calculations to nonrelativistic GIAO isotropic shielding tensors. The calculated isotropic shielding tensors can be utilized in the spectroscopic assignment of the 77Se chemical shifts of novel selenium-halogen molecules and cations. The experimental FT-Raman spectra of (SeI3)[AsF6] in the solid state and in SO2(l) solution are also reported.

Experimental and theoretical investigations of tellurium(IV) diimides and imidotelluroxanes: X-ray structures of B(C6F5)3 adducts of OTe(mu-NtBu)2TeNtBu, [OTe(mu-NtBu)2Te(mu-O)]2 and tBuNH2.

The hydrolysis of (t)BuNTe(mu-N(t)Bu)(2)TeN(t)Bu (1) with 1 or 2 equiv of (C(6)F(5))(3)B.H(2)O results in the successive replacement of terminal imido groups by oxo ligands to give the telluroxane-Lewis acid adducts (C(6)F(5))(3)B.OTe(mu-N(t)Bu)(2)TeN(t)Bu (2) and [(C(6)F(5))(3)B.OTe(mu-N(t)Bu)(2)Te(mu-O)](2) (3), which were characterized by multinuclear NMR spectroscopy and X-ray crystallography. The Te=O distance in 2 is 1.870(2) A. The di-adduct 3 involves the association of four (t)()BuNTeO monomers to give a tetramer in which both terminal Te=O groups [d(TeO) = 1.866(3) A] are coordinated to B(C(6)F(5))(3). The central Te(2)O(2) ring in 3 is distinctly unsymmetrical [d(TeO) = 1.912(3) and 2.088(2) A]. The X-ray structure of (C(6)F(5))(3)B.NH(2)(t)()Bu (4), the byproduct of these hydrolysis reactions, is also reported. The geometries and energies of tellurium(IV) diimides and imido telluroxanes were determined using quantum chemical calculations. The calculated energies for the reactions E(NR)(2) + Te(NR)(2) (E = S, Se, Te; R = H, Me, (t)Bu, SiMe(3)) confirm that cyclodimerization of tellurium(IV) diimides is strongly exothermic. In the mixed-chalcogen systems, the cycloaddition is energetically favorable for the Se/Te combination. The calculated energies for the further oligomerization of the dimers XE(mu-NMe)(2)EX (E = Se, Te; X = NMe, O) indicate that the formation of tetramers is strongly exothermic for the tellurium systems but endothermic (X = NMe) or thermoneutral (X = O) for the selenium systems, consistent with experimental observations.

Electronic structures and molecular properties of chalcogen nitrides Se2N2 and SeSN2.

The electronic structures and molecular properties of S2N2 as well as the currently unknown chalcogen nitrides Se2N2 and SeSN2 have been studied using various ab initio and density functional methods. All molecules share a qualitatively similar electronic structure and can be primarily described as 2pi-electron aromatics having minor singlet diradical character of 6-8% that can be attributed solely to the nitrogen atoms. This diradical character is manifested in the prediction of their molecular properties, in which coupled cluster and multiconfigurational approaches, as well as density functional methods, show the best performance. The conventional ab initio methods RHF and MP2 completely fail to describe these systems. Predictions for the vibrational frequencies, IR intensities, Raman activities, and 14N, 15N, and 77Se chemical shifts, as well as singlet excitation energies of Se2N2 and SeSN2, have been made. The computed high-level spectroscopic data will be of considerable value in future efforts aimed at the preparation of the conducting polymers (SeN)x and (SeNSN)x.

Thermal and spectroscopic investigation of europium and samarium sulphates hydrates by TG-FTIR and ICP-MS techniques.

The investigation of europium(III) sulphate hydrate and samarium(III) sulphate hydrate was performed by thermal analysis (TG-DTG) and simultaneous infrared evolved gas analysis-Fourier transformed infrared (EGA-FTIR) spectroscopy. The TG, DTG and DTA curves were recorded at the 25-1400 degrees C in the dynamic air atmosphere by TG/DTA analyser. The infrared evolved gas analysis was obtained on the FTIR spectrometer. Eu(2)(SO(4))(3).nH(2)O (n=3.97) and Sm(2)(SO(4))(3).nH(2)O (n=8.11) were analysed, the dehydration and decomposition steps were investigated and the water content was calculated. The formation of different oxysulphates was studied. The trace rare earth elements in Eu and Sm sulphates were determined by ICP-MS. The concentration of trace Eu, Sm, La, Gd, Y and Ce ranged from 3.9x10(-6) to 1.5x10(-4)% (m/m).

Ca[Ag2(SCN)4].2H2O.

Calcium tetrathiocyanatodiargentate(I) dihydrate, Ca[Ag(2)(SCN)(4)].2H(2)O, contains eight-membered Ag(4)S(4) rings bonded together through shared atoms to form layers parallel to (100). The thiocyanate groups link the layers to Ca-O chains running parallel to the c axis. The Ca atom is located on a twofold rotation axis parallel to b and is surrounded by four water molecules of crystallization and four thiocyanate N atoms in a distorted square antiprism.

Experimental and theoretical investigations of structural trends for selenium(IV) imides and oxides: X-ray structure of Se3(NAd)2.

The thermal decomposition of Se(NAd)(2) (Ad = 1-adamantyl) in THF was monitored by (77)Se NMR and shown to give the novel cyclic selenium imide Se(3)(NAd)(2) as one of the products. An X-ray structural determination showed that Se(3)(NAd)(2) is a puckered five-membered ring with d(Se-Se) = 2.404(1) A and |d(Se-N)| = 1.873(4) A. On the basis of (77)Se NMR data, other decomposition products include the six-membered ring Se(3)(NAd)(3), and the four-membered rings AdNSe(micro-NAd)(2)SeO and OSe(micro-NAd)(2)SeO. The energies for the cyclodimerization of E(NR)(2) and RNEO (E = S, Se; R = H, Me, (t)Bu, SiMe(3)), and the cycloaddition reactions of RNSeO with E(NR)(2), RNSO(2) with Se(NR)(2), and S(NR)(2) with Se(NR)(2) have been calculated at MP2, CCSD, and CCSD(T) levels of theory using the cc-pVDZ basis sets and B3PW91/6-31G* optimized geometries. Sulfur(IV) and selenium(IV) diimide monomers are predicted to be stable, the sole exception being Se(NSiMe(3))(2) that shows a tendency toward cyclodimerization. The cyclodimerization energy for RNSeO and the cycloaddition reaction energies of RNSeO with Se(NR)(2) as well as that of RNSO(2) with Se(NR)(2) are negative, consistent with the observed formation of OSe(micro-N(t)Bu)(2)SeO, OSe(micro-N(t)Bu)(2)SeN(t)Bu, and O(2)S(micro-N(t)Bu)(2)SeN(t)Bu, respectively. Cycloaddition is unlikely when one of the reactants is a sulfur(IV) diimide.

Conformations and energetics of sulfur and selenium diimides.

The geometries and energetics of different conformations of sulfur and selenium diimides E(NR)(2) (E = S, Se; R = H, Me, (t)Bu, C(6)H(3)Me(2)-2,6, SiMe(3)) have been studied by using various ab initio and DFT molecular orbital techniques. The syn,syn conformation is found to be most stable for parent E(NH)(2), but in general, the preferred molecular conformation for substituted chalcogen diimides is syn,anti. In the case of E(NH)(2) the present calculations further confirm that syn,syn and syn,anti conformations lie energetically close to each other. From the three different theoretical methods used, B3PW91/6-31G proved to be the most suitable method for predicting the geometries of chalcogen diimides. The optimized geometrical parameters are in a good agreement with all available experimental data. While qualitative energy ordering of the different conformations is independent of the level of theory, the quantitative energy differences are dependent on the method used. The performance and reliability of higher level ab initio calculations and DFT methods using large basis sets were tested and compared with experimental information where available. All of the higher level ab inito methods give very similar results, but the use of large basis sets with the B3PW91 method does not increase the reliability of the results. The combination of CCSD(T)/cc-pVDZ with the B3PW91/6-31G-optimized geometries is found to be the method of choice to study energetic properties of chalcogen diimides.

Polymorphism in Cs[AgZn(NCS)4].

The title compound, caesium silver zinc tetrathiocyanate, crystallizes in two polymorphic forms, in space groups P2(1)/n and C2/c. Both structures form a continuous three-dimensional network. The structure in C2/c contains a delocalized Ag atom in a binuclear-like anion, where two [Ag(NCS)(4)] units (delocalized Ag as an average) share two common NCS(-) ligands.

Cs[Ag4Zn2(SCN)9].

Caesium tetrasilver dizinc nonathiocyanate, Cs[Ag(4)Zn(2)(SCN)(9)], forms a continuous structure, where the Ag atoms and the S atoms of the thiocyanate groups form chains which run along [101]. These chains are bonded together through the Cs and Zn atoms. It is not possible to distinguish between space groups P1 and P-1, but, if the latter space group is correct, the structure contains a thiocyanate group disordered across a centre of inversion. The structure is described in space group P-1, in which the Cs atom also lies on a centre of inversion.

Preparation and structural characterization of (Me(3)SiNSN)(2)Se, a new synthon for sulfur-selenium nitrides.

The reaction of (Me(3)SiN)(2)S with SeCl(2) (2:1 ratio) in CH(2)Cl(2) at -70 degrees C provides a route to the novel mixed selenium-sulfur-nitrogen compound (Me(3)SiNSN)(2)Se (1). Crystals of 1 are monoclinic and belong the space group P2(1)/c, with a = 7.236(1) A, b = 19.260(4) A, c = 11.436(2) A, beta = 92.05(3) degrees, V = 1592.7(5) A(3), Z = 4, and T = -155(2) degrees C. The NSNSeNSN chain in 1 consists of Se-N single bonds (1.844(3) A) and S=N double bonds (1.521(3)-1.548(3) A) with syn and anti geometry at the N=S=N units. The N-Se-N bond angle is 91.8(1) degrees. The EI mass spectrum shows a molecular ion with good agreement between the observed and calculated isotopic distributions. The (14)N NMR spectrum exhibits two resonances at -65 and -77 ppm. Both (13)C and (77)Se NMR spectra show single resonances at 0.83 and 1433 ppm, respectively. The reaction of 1 with an equimolar amount of SeCl(2) produces 1,5-Se(2)S(2)N(4) (2) in a good yield, and that of (Me(3)SiNSN)(2)S with SCl(2) affords S(4)N(4) (3), but the reactions of (Me(3)SiNSN)(2)Se with SCl(2) and (Me(3)SiNSN)(2)S with SeCl(2) result in the formation of a mixture of 2 and 3. A likely reaction pathway involves the intermediate formation of E(2)N(2) fragments (E = S, Se).

Dicaesium silver zinc thiocyanate, Cs2[AgZn(SCN)5].

The title compound, dicaesium(I)-mu-thiocyanato-kappa2N:S-zinc(II)-tetra-mu-thiocyanato-kappa2S:N-argentate(I), crystallizes in the orthorhombic space group Pmn2(1) and contains units of composition AgZn(SCN)3 lying on a mirror plane and bonded together through Cs+ ions and thiocyanate groups. The crystal studied contained equal numbers of inversion twins.

Calcium dicaesium silver thiocyanate dihydrate.

The title compound, CaCs2[Ag2(SCN)6]*2H2O, forms a continuous structure where the Ag atoms form chains with S atoms in the c-axis direction. The chains are bonded together through Cs and Ca atoms. The crystal water of the structure is bonded to the Ca atoms, which lie on centers of symmetry.

Alkoxo Bound Monooxo- and Dioxovanadium(V) Complexes: Synthesis, Characterization, X-ray Crystal Structures, and Solution Reactivity Studies.

A large variety of oxovanadium(V) complexes, mononuclear VO(2)(+) and VO(3+) in addition to the dinuclear VO(3+), of the structural type (VOL)(2), (VOHL)(2), VOLHQ, K(VO(2)HL), K(VO(2)H(2)L), or (salampr) (VO(2)L) {where L = Schiff base ligand possessing alkoxo group(s); HQ = 8-hydroxyquinoline; salampr = cation of reduced Schiff base derived from salicylaldehyde and 2-amino-2-methylpropan-1-ol}, bound to alkoxo, phenolate and imine groups have been synthesized in high yields and characterized by several spectral and analytical methods, including single crystal X-ray studies. While the mononuclear VO(2)(+) complexes have been synthesized at alkaline pH, the dinuclear VO(3+) complexes have been synthesized under neutral conditions using alkoxo rich Schiff base ligands. The X-ray structures indicate that the cis-dioxo complexes showed longer V-O(alkoxo) bond lengths compared to the monooxo counterparts. The plot of V-O(phen) bond distances of several VO(3+) complexes vs the lmct showed a near linear correlation with a negative slope. The cyclic voltammograms revealed a reversible V(V)/V(IV) couple with the reduction potentials increasing to more negative ones as the number of alkoxo groups bound to V increases from 1 to 2. Moreover, the cis-dioxo VO(2)(+) complexes are easier to reduce than their monooxo counterparts. The solution stability of these complexes was studied in the presence of added water (1:4, water:solvent), where no decomposition was observed, unlike other Schiff base complexes of V. The conversion of the dioxo complexes to their monooxo counterparts in the presence of catalytic amounts of acid is also demonstrated. The reactivity of alkoxo bound V(V) complexes is also reported. X-ray parameters are as follows. H(4)L(3): monoclinic space group, P2(1)/c; a = 10.480(3), b = 8.719(6), c = 12.954(8) Å; beta = 101.67(4) degrees; V = 1126(1) Å(3); Z = 4; R = 0.060, R(w) = 0.058. Complex 1: monoclinic space group, P2(1)/n; a = 12.988(1), b = 9.306(2), c = 19.730(3) Å; beta = 99.94(1) degrees; V = 2348.9(7) Å(3); Z = 4; R = 0.031, R(w) = 0.027. Complex 2: monoclinic space group, P2(1)/n; a = 12.282(3), b = 11.664(2), c = 12.971(4) Å; beta = 97.89(2) degrees; V = 1840.5(8) Å; Z = 4; R = 0.035, R(w) = 0.038. Complex 5: monoclinic space group, P2(1)/c; a = 17.274(2), b = 6.384(2), c = 16.122(2) Å; beta = 116.67(1) degrees; V = 1588.7(7) Å(3); Z = 4; R = 0.039, R(w) = 0.043. Complex 8: monoclinic space group, P2(1)/c; a = 11.991(1), b = 11.696(4), c = 12.564(3) Å; beta = 110.47(1) degrees; V = 1650.8(8) Å(3); Z = 2; R = 0.045, R(w) = 0.049.