New heteroleptic bis-phenanthroline copper(I) complexes with dipyridophenazine or imidazole fused phenanthroline ligands: spectral, electrochemical, and quantum chemical studies.

Two new sterically challenged diimine ligands L(1) (2,9-dimesityl-2-(4'-bromophenyl)imidazo[4,5-f][1,10]phenanthroline) and L(2) (3,6-di-n-butyl-11-bromodipyrido[3,2-a:2',3'-c]phenazine) have been synthesized with the aim to build original heteroleptic copper(I) complexes, following the HETPHEN concept developed by Schmittel and co-workers. The structure of L(1) is based on a phen-imidazole molecular core, derivatized by two highly bulky mesityl groups in positions 2 and 9 of the phenanthroline cavity, preventing the formation of a homoleptic species, while L(2) is a dppz derivative, bearing n-butyl chains in α positions of the chelating nitrogen atoms. The unambiguous formation of six novel heteroleptic copper(I) complexes based on L(1), L(2), and complementary matching ligands (2,9-R(2)-1,10-phenanthroline, with R = H, methyl, n-butyl or mesityl) has been evidenced, and the resulting compounds were fully characterized. The electronic absorption spectra of all complexes fits well with DFT calculations allowing the assignment of the main transitions. The characteristics of the emissive excited state were investigated in different solvents using time-resolved single photon counting and transient absorption spectroscopy. The complexes with ligand L(2), bearing a characteristic dppz moiety, exhibit a very low energy excited-state which mainly leads to fast nonradiative relaxation, whereas the emission lifetime is higher for those containing the bulky ligand L(1). For example, a luminescence quantum yield of about 3 × 10(-4) is obtained with a decay time of about 50 ns for C2 ([Cu(I)(nBu-phen)(L(1))](+)) with a weak influence of strong coordinating solvent on the luminescence properties. Overall, the spectral features are those expected for a highly constrained coordination cage. Yet, the complexes are stable in solution, partly due to the beneficial π stacking between mesityl groups and vicinal phenanthroline aromatic rings, as evidenced by the X-ray structure of complex C3 ([Cu(I)(Mes-phen)(L(2))](+)). Electrochemistry of the copper(I) complexes revealed reversible anodic behavior, corresponding to a copper(I) to copper(II) transition. The half wave potentials increase with the steric bulk at the level of the copper(I) ion, reaching a value as high as 1 V vs SCE, with the assistance of ligand induced electronic effects. L(1) and L(2) are further end-capped by a bromo functionality. A Suzuki cross-coupling reaction was directly performed on the complexes, in spite of the handicapping lability of copper(I)-phenanthroline complexes.

Ion chemistry of VX surrogates and ion energetics properties of VX: new suggestions for VX chemical ionization mass spectrometry detection.

Room temperature rate constants and product ion branching ratios have been measured for the reactions of numerous positive and negative ions with VX chemical warfare agent surrogates representing the amine (triethylamine) and organophosphonate (diethyl methythiomethylphosphonate (DEMTMP)) portions of VX. The measurements have been supplemented by theoretical calculations of the proton affinity, fluoride affinity, and ionization potential of VX and the simulants. The results show that many proton transfer reactions are rapid and that the proton affinity of VX is near the top of the scale. Many proton transfer agents should detect VX selectively and sensitively in chemical ionization mass spectrometers. Charge transfer with NO(+) should also be sensitive and selective since the ionization potential of VX is small. The surrogate studies confirm these trends. Limits of detection for commercial and research grade CIMS instruments are estimated at 80 pptv and 5 ppqv, respectively.

Theoretical proton affinity and fluoride affinity of nerve agent VX.

Proton affinity and fluoride affinity of nerve agent VX at all of its possible sites were calculated at the RI-MP2/cc-pVTZ//B3LYP/6-31G* and RI-MP2/aug-cc-pVTZ//B3LYP/6-31+G* levels, respectively. The protonation leads to various unique structures, with H(+) attached to oxygen, nitrogen, and sulfur atoms; among which the nitrogen site possesses the highest proton affinity of -ΔE ∼ 251 kcal/mol, suggesting that this is likely to be the major product. In addition some H(2), CH(4) dissociation as well as destruction channels have been found, among which the CH(4) + [Et-O-P(═O)(Me)-S-(CH(2))(2)-N(+)(iPr)═CHMe] product and the destruction product forming Et-O-P(═O)(Me)-SMe + CH(2)═N(+)(iPr)(2) are only 9 kcal/mol less stable than the most stable N-protonated product. For fluoridization, the S-P destruction channel to give Et-O-P(═O)(Me)(F) + [S-(CH(2))(2)-N-(iPr)(2)](-) is energetically the most favorable, with a fluoride affinity of -ΔE ∼ 44 kcal. Various F(-) ion-molecule complexes are also found, with the one having F(-) interacting with two hydrogen atoms in different alkyl groups to be only 9 kcal/mol higher than the above destruction product. These results suggest VX behaves quite differently from surrogate systems.