Molecular structures of two unexpected metal complexes obtained from additions of coordinated phosphines to acetylenes

The syntheses and structures of two new compounds are reported. The first compound, [Cr(CO)₄]₂[C₄F₂(PPh₂)₄], obtained from Cr(CO)₄(PPh₂H)₂ and CF₃CCF₃ in the presence of one equivalent of BuLi has a structure with the ligand 1,2,3,4-tetrakis(diphenylphosphino)-1,4-difluorobutadiene chelating to two Cr(CO)₄ groups via the 1,4 and 2,3 phosphine groups. A mechanism for the formation of this compound is suggested which involves sequential deprotonation of a phosphine, nucleophilic attack on the fluorocarbon, and fluoride ion elimination. The second compound, CrC₃₆H₂₈P₂O₇, arises from a similar base promoted reaction of Cr(CO)₄-(PPhH₂)₂ and PhCCCOOEt. Here the expected initial product from cyclization of these reactants acts as a nucleophile to attack a second equivalent of the acetylene. The intermediate carbanion from this reaction can undergo a ring closure by displacement of OEt^-, giving the observed product.     

Vibrational spectrum of I(H2O)

The infrared spectrum of the ionic cluster I⁻(H₂O) was recorded from 3170 to 3800 cm⁻¹ by vibrational predissociation spectroscopy. A strong multiplet observed at 3415 cm⁻¹ and a narrow band at 3710 cm⁻¹ were assigned as a hydrogen-bonded OH stretch and free OH stretch respectively, indicating that H₂O forms a single hydrogen bond with the iodide anion. Ab initio vibrational frequencies and intensities were computed at the second-order Møller-Plesset (MP2) level for the minimum energy configuration, a nearly linear hydrogen-bonded isomer, and for a low-lying saddlepoint, a symmetric C_2v bridged isomer. The spectrum predicted for the hydrogen-bonded isomer agreed well with experiment.     

Solvent-assisted catalysis mechanism on Keto–enol tautomerism of cyameluric acid

The keto–enol tautomerism of cyameluric acid, both in gas phase and in water and methanol solution, has been studied at the B3LYP/6-31++g(d,P) level of theory in this paper. The harmonic frequencies of all the structures are calculated. The results show that the transition states of the tautomerism are 4-membered ring conformations in gas phase, whereas 6-membered ring conformations in solution. In the first proton transfer, activation energy ΔE^# is 56.4 and 50.9 kJ/mol for water and methanol solution, respectively, which is much lower than that in gas phase (163.2 kJ/mol). Solvent molecules (water and methanol) produce an important catalytic effect in the tautomerism, especially for methanol-solvated system. NBO analysis shows that there is a strong interaction between cyameluric acid and solvent molecules in transition states. AIM charge analysis indicates that the keto–enol tautomerism shows a certain degree of proton transfer character. From the reaction enthalpy and reaction rate point of view, keto–enol tautomerism in water-solvated and methanol-solvated system is easier than that in gas phase. The keto–enol tautomerisms are endothermic both in gas phase and in solution, so the enol forms are less stable than the keto ones.     

Two-fluid electroosmotic flow in microchannels

This paper presents a mathematical model to describe a two-fluid electroosmotic pumping technique, in which an electrically non-conducting fluid is delivered by the interfacial viscous force of a conducting fluid; the latter is driven by electroosmosis. The electrical potential in the conducting fluid and the analytical solution of the steady two-fluid electroosmotic stratified flow in a rectangular microchannel was presented by assuming a planar interface between the two immiscible fluids. The effects of viscosity ratio, hold-up, concentration, and interfacial zeta potential are analyzed to show the potential feasibility of this technique.     

Ultraviolet protection factors for clothing: an intercomparison of measurement systems

In recent years the need to standardize measurement protocols for quantifying the degree of ultraviolet radiation (UVR) protection provided by clothing has led to the introduction of a number of standards around the world. To date, these standards have specified spectral measurements of UVR transmission by clothing and fabrics. Development of a standard test method has become an important part of the testing process, and this article presents results from an intercomparison involving 10 independent testing laboratories and 11 different UVR transmission measurement instruments. In addition to comparing the measured ultraviolet protection factors (UPF), this intercomparison also incorporates detailed scan results from all 10 laboratories and highlights differences in performance of the various instruments in different wavelength regions. Careful examination of these differences can indicate where changes to the systems could be made to allow improvements both in equipment performance and in agreement of the final results. The variability in the measurements of UPF in this study suggest that the protection categories in standards may need to be broadened.     

A trinuclear heterobimetallic Ru(II)/Pt(II) complex as a chemodosimeter selective for sulfhydryl-containing amino acids and peptides

A trinuclear heterobimetallic Ru(II)/Pt(II) complex, cis-{Ru(phen)2[CN-Pt(DMSO)Cl2]2} (phen = 1,10-phenanthroline), is able to function as a "switch-on" luminescent chemodosimeter for sulfhydryl-containing amino acids and peptides via specific binding of the amino acids/peptides with the Pt(II) centers and the subsequent cleavage of the Ru(II)-Pt(II) cyano-bridge.     

On constrained multivariate splines and their approximations

Summary The variational formulation of multivariate spline functions is generalized to include cases where the function has to satisfy inequality constraints such as positivity and convexity. Condition for existence and uniqueness of a solution is given. Approximation to the solution can be obtained by solving the variational problem in a finite dimensional subspace. Conditions for convergence and error estimates of the approximations are presented, both for interpolation problems and smoothing problems. The general theory is illustrated by specific examples including the volume-matching problem and the one-sided thin plate spline.This research is partially supported by the U.S. Army Contract No. DAAG 29-77-G-0207, and by NSF Grant No. MCS-8101836Part of this paper is based on Chapters 2 and 3 of the author's Ph. D. thesis. The author would like to express his sincere thanks to Professor Grance Wahba and to two referees for many helpful comments     

The preparation and characterization of a platinum ether complex

The reaction of [Pt((F₃C)CCH(CF₃))(P(C₂H₅)₃)₂CH₃OH]PF₆ with allene in methanol affords a novel metallocyclic ethereal complex [$\text{Pt((F}{}_3\text{C)CHC(CF}{}_3\text{)C(CH}{}_3\text{)CH}{}_2\text{O}$CH₃)(P(C₂H₅)₃)₂]PF₆, which has been characterized by ¹H, ²H, ¹⁹F and ³¹P NMR spectroscopy. Its structure has also been determined by a single crystal X-ray analysis. The crystal are monoclinic, space group P2₁/n, with cell dimensions a 20.012(5), b 17.222(5), c 8.902(3) Å and β 91.54(5)°. The structure was refined by full matrix least-squares methods on F, using 3097 unique observations collected by automated four circle diffractometer. Refinement converged at R  0.066. The Pt atom has a distorted square-planar coordination geometry, with cis P atoms, and PtP distances of 2.219(4) Å (trans to O) and 2.324(4) Å (trans to C). These results show the ethereal group is a weak ligand to platinum(II) but because of the chelating effect, its displacement by other ligands is thermodynamically not favorable. The mechanism of formation of the ethereal complex is also discussed.     

Probing ruthenium-acetylide bonding interactions: synthesis, electrochemistry, and spectroscopic studies of acetylide-ruthenium complexes supported by tetradentate macrocyclic amine and diphosphine ligands

The synthesis and spectroscopic properties of trans-[RuL4(C[triple bond]CAr)2] (L4 = two 1,2-bis(dimethylphosphino)ethane, (dmpe)2; 1,5,9,13-tetramethyl-1,5,9,13-tetraazacyclohexadecane, 16-TMC; 1,12-dimethyl-3,4:9,10-dibenzo-1,12-diaza-5,8-dioxacyclopentadecane, N2O2) are described. Investigations into the effects of varying the [RuL4] core, acetylide ligands, and acetylide chain length for the [(-)C[triple bond]C(C6H4C[triple bond]C)(n-1)Ph] and [(-)C[triple bond]C(C6H4)(n-1)Ph] (n = 1-3) series upon the electronic and electrochemical characteristics of trans-[RuL4(C[triple bond]CAr)2](0/+) are presented. DFT and TD-DFT calculations have been performed on trans-[Ru(L')4(C[triple bond]CAr)2](0/+) (L' = PH3 and NH3) to examine the metal-acetylide pi-interaction and the nature of the associated electronic transition(s). It was observed that (1) the relationship between the transition energy and 1/n for trans-[Ru(dmpe)2{C[triple bond]C(C6H4C[triple bond]C)(n-1)Ph}2] (n = 1-3) is linear, and (2) the sum of the d(pi)(Ru(II)) --> pi*(C[triple bond]CAr) MLCT energy for trans-[Ru(16-TMC or N2O2)(C[triple bond]CAr)2] and the pi(C[triple bond]CAr) --> d(pi)(Ru(III)) LMCT energy for trans-[Ru(16-TMC or N2O2)(C[triple bond]CAr)2]+ corresponds to the intraligand pi pi* absorption energy for trans-[Ru(16-TMC or N2O2)(C[triple bond]CAr)2]. The crystal structure of trans-[Ru(dmpe)2{C[triple bond]C(C6H4C[triple bond]C)2Ph}2] shows that the two edges of the molecule are separated by 41.7 A. The electrochemical and spectroscopic properties of these complexes can be systematically tuned by modifying L4 and Ar to give E(1/2) values for oxidation of trans-[RuL4(C[triple bond]CAr)2] that span over 870 mV and lambda(max) values of trans-[RuL4(C[triple bond]CAr)2] that range from 19,230 to 31,750 cm(-1). The overall experimental findings suggest that the pi-back-bonding interaction in trans-[RuL4(C[triple bond]CAr)2] is weak and the [RuL4] moiety in these molecules may be considered to be playing a "dopant" role in a linear rigid pi-conjugated rod.