P NMR studies on the Mer-fac isomerization of Pt(S4N4)Cl2(PMe2Ph)

When heated in chloroform the meridional S₄N₄²⁻ complex, Pt(S₄N₄)Cl₂ (PMe₂Ph), readily isomerizes, giving a product which has, on the basis of ¹⁵N-labelling studies, been identified as the facial isomer.     

Hydrothermal syntheses and crystal structures of bimetallic cluster complexes [{Cd(phen)2}2V4O12]·5H2O and [Ni(phen)3]2[V4O12]·17.5H2O

The hydrothermal reactions of vanadium oxide starting materials with divalent transition metal cations in the presence of nitrogen donor chelating ligands yield the bimetallic cluster complexes with the formulae [{Cd(phen₂)₂V₄O₁₂]·5H₂O (1) and [Ni(phen)₃]₂[V₄O₁₂]·17.5H₂O (2). Crystal data: C₄₈H₅₂Cd₂N₈O₂₂V₄ (1), triclinic. a=10.3366(10), b=11.320(3), c=13.268(3) Å, =103.888(17)°, β=92.256(15)°, γ=107.444(14)°, Z=1; C₇₂H₁₃₁N₁₂Ni₂O_29.5V₄ (2), triclinic. a=12.305(3), b=13.172(6), c=15.133(4), =79.05(3)°, β=76.09(2)°, γ=74.66(3)°, Z=1. Data were collected on a Siemens P4 four-circle diffractometer at 293 K in the range 1.59° <θ<26.02° and 2.01°<θ<25.01° using the ω-scan technique, respectively. The structure of 1 consists of a [V₄O₁₂]⁴⁻ cluster covalently attached to two {Cd(phen)₂}²⁺ fragments, in which the [V₄O₁₂]⁴⁻ cluster adopts a chair-like configuration. In the structure of 2, the [V₄O₁₂]⁴⁻ cluster is isolated. And the complex formed a layer structure via hydrogen bonds between the [V₄O₁₂]⁴⁻ unit and crystallization water molecules.     

S2 → S0 fluorescence in an aromatic thioketone, xanthione

In addition to the red phosphorescence (T₁(³ A₂n, π^*) → S₀) xanthione exhibits in solution an emission with a maximum at ≈ 23 000 cm⁻¹ and φ_f(298°) = 5 × 10⁻³. It is shown that this emission is fluorescence from the second excited singlet state (S₂ (¹A₁ π, π^*) → S₀).     

A localized molecular orbital study on the bonding of> Mo3S4]2Mo> and> Mo3S4]CuI> versus (C6H6)2Cr and C6H6Cr(CO)3

The energy-localized CNDO/2 molecular orbitais have been calculated for the clusters containing molybdenum, > {Mo₃S₄₂Mo}⁸⁺ and> Mo₃S₄]CuI> ⁴⁺, versus the prototype arene-metal sandwich (C₆H₆)₂Cr and half-sandwich complexes C₆H₆Cr(CO)₃. The bonding characteristics of these compounds are described from a localization bonding viewpoint. There are two typical M-arene and M-[Mo₃S₄] bondings. One is formed by electron donation from the three-center two-electron π-bonds in the arene or [Mo₃S₄]⁴⁺ ligands into the vacant hybrid orbitais of the “stranger” metal atom. In the other M-arene or M-[Mo₃S₄] bond there is very little donation by the lone electron pair occupying the d AOs of the “stranger” metal atom to the arene or [Mo₃S₄]⁴⁺ ligands. The analogy of the ligand [Mo₃S₄]⁴⁺ in the clusters studied with the ligand benzene is also briefly discussed.     

Low-lying excited singlet states and S2→S0 luminescence of dipyrido[3,4-b: 2,3-d]phenazine

The absorption, fluorescence and excitation fluorescence spectra dipyrido[3,4-b:2,3-d]-phenazine (DPPZ1) have been measured in non-polar and polar matrices at room temperature, and were taken into account to explain the origin of the relatively weak emission of this molecule in both type of environment. The electronic structure of DPPZ1 was calculated using a modified INDO CI method. The geometry optimization has been performed using the MNDO method. According to the spectra and the results of calculations, the lowest excited singlet state S₁ of DPPZ1 molecule is of n,π^*-type and the next one, S₂ state, is of π,π^*-type. The energy gap ΔE_calc is equal 4770 cm⁻¹. The low efficiency of the emission observed in the hydroxylic solvent can be interpreted in terms of thermal quenching of the π,π^*-type fluorescence. However, experimental results obtained suggest that in nonpolar solvents the emission of the molecule examined is an anomalous S₂→S₀ fluorescence.     

Electronically excited states of disulphur dinitride (S2N2) and its conversion to the metallic polymer (SN)x

Ab initio configuration interaction calculations with a double zeta basis augmented by polarisation functions have been carried out for all the lowest singlet and triplet states of S₂N₂ and (SN)₂) - a unit of the polymer (SN)_x. The results satisfactory account for the UV-absorption spectrum of S₂N₂ which is probably dominated by ¹B_2u. There are low-lying singlet and triplet states for (SN)₂, and one of these a σσ* triplet seems likely to be the polymerisation precursor.     

Synthesis and structure of a new selenium-bridged tungsten cluster, [W3Se7(S2P(OEt)2)3]Br

[W₃Se₇(S₂P(OEt)₂)₃]Br was prepared by reacting (Et₄N)₂W₃Se₇Br₆ with KS₂P (OEt)₂ in CH₃CN and its crystal structure determined. In the [W₃(μ₃-Se)(μ₂-Se₂)₃]⁴⁺ core the W---W bond length is 2.755(5)-2.764(6) Å and the Se---Se bond length is 2.32(1)- 2.34(4) Å.     

Reaction of the tetrasulphidomolybdenum(IV) complex LMo(NCS)(S4) with dicarbomethoxyacetylene: X-ray structure of LMo(NCS){S2C2(CO2Me)2} [L = hydrotris(3,5-dimethylpyrazolyl)borate]

The reaction of {HB(Me₂pz)₃}Mo(NCS)(S₄) [HB(Me₂pz)₃⁻ = hydrotris(3,5-dimethylpyrazolyl)borate anion] with dicarbomethoxyacetylene in refluxing toluene results in the formation of the brown, diamagnetic complex {HB(Me₂pz)₃}Mo(NCS){S₂C₂(CO₂Me)₂} (1) (the reactants above also yield 1 upon prolonged reaction in dichloromethane at 25°C), which has been characterized by X-ray crystallography. The mononuclear pseudo-octahedral complex contains a facially tridentate HB(Me₂pz)₃⁻ ligand, a monodentate N-bound NCS⁻ ligand, and a bidentate S₂C₂(CO₂Me)₂²⁻ ligand having a near planar MoS₂C₄ fragment and a SC=CS bond distance of 1.342(15) Å. Solutions of 1 are unstable in air and decompose to produce {HB(Me₂pz)₃}MoO₂(NCS) and {HB(Me₂pz)₃}MoO(NCS)₂.     

Theoretical studies of third-order nonlinear optical response for B12N12, B24N24 and B36N36 clusters

In this paper, we have calculated the third-order nonlinear optical polarizabilities corresponding to three optical processes: third-harmonic generation (THG), electric-field-induced second-harmonic generation (EFISHG) and degenerate four-wave mixing (DFWM) for B₁₂N₁₂, B₂₄N₂₄ and B₃₆N₃₆ clusters. The calculations have been performed by employing ab initio time-dependent density functional theory combined with sum-over-states method (SOS//TDDFT). We obtained the similar dynamic behavior of third-order NLO polarizabilities for three BN clusters. At input photon energy below 1.25 eV, the resonance enhancements of response haven't occurred. This is due to the fact that the calculated BN clusters have the large transition energy. B₂₄N₂₄ cluster has the larger transition dipole moments and the third-order polarizabilities of B₂₄N₂₄ are much larger than those of B₁₂N₁₂ and B₃₆N₃₆. We also estimate the static third-order optical susceptibility χ⁽³⁾ for BN fullerene materials from the average static third-order polarizability <γ>. The static χ⁽³⁾ of B₂₄N₂₄ fullerene materials are 1.36×10⁻¹⁴ esu for three NLO processes.     

Thermal studies of novel molecular perovskite energetic material (C6H14N2)[NH4(ClO4)3]

(C6H(14)N2)[NH4(ClO4)3] is a newly developed porous hybrid inorganic-organic framework material with easy access and excellent detonation performances,however,its thermal properties is still unclear and severely hampered further applications.In this study,thermal behaviors and non-isothermal decomposition reaction kinetics of(C6H(14)N2)[NH4(ClO4)3] were investigated systematically by the combination of differential scanning calorimetry(DSC) and simultaneous thermal analysis methods.In-situ FTIR spectroscopy technology was applied for investigation of the structure changes of(C6H(14)N2) NH4(ClO4)3]and some selected referents for better understanding of interactions between different components during the heating process.Experiment results indicated that the novel molecular perovskite structure renders(C6H(14)N2)[NH4(ClO4)3] better thermal stability than most of currently used energetic materials.Underhigh temperature s,the stability of the cage skeleton constructed by NH4^+and ClO4^-ions determined the decomposition process rather than organic moiety confined in the skeleton.The simple synthetic method,good detonation performances and excellent thermal properties make(C6H(14)N2)[NH4(ClO4)3] an ideal candidate for the preparation of advanced explosives and propellants.