Gold(I) phosphido complexes: synthesis, structure, and reactivity

Deprotonation of the phosphine complexes Au(PHR(2))Cl with aqueous ammonia gave the gold(I) phosphido complexes [Au(PR(2))](n)() (PR(2) = PMes(2) (1), PCy(2) (2), P(t-Bu)(2) (3), PIs(2) (4), PPhMes (5), PHMes (6); Mes = 2,4,6-Me(3)C(6)H(2), Is = 2,4,6-(i-Pr)(3)C(6)H(2), Mes = 2,4,6-(t-Bu)(3)C(6)H(2), Cy = cyclo-C(6)H(11)). (31)P NMR spectroscopy showed that these complexes exist in solution as mixtures, presumably oligomeric rings of different sizes. X-ray crystallographic structure determinations on single oligomers of 1-4 revealed rings of varying size (n = 4, 6, 6, and 3, respectively) and conformation. Reactions of 1-3 and 5 with PPN[AuCl(2)] gave PPN[(AuCl)(2)(micro-PR(2))] (9-12, PPN = (PPh(3))(2)N(+)). Treatment of 3 with the reagents HI, I(2), ArSH, LiP(t-Bu)(2), and [PH(2)(t-Bu)(2)]BF(4) gave respectively Au(PH(t-Bu)(2))(I) (14), Au(PI(t-Bu)(2))(I) (15), Au(PH(t-Bu)(2))(SAr) (16, Ar = p-t-BuC(6)H(4)), Li[Au(P(t-Bu)(2))(2)] (17), and [Au(PH(t-Bu)(2))(2)]BF(4) (19).     

Kinetics of destruction of diisopropyl methylphosphonate in corona discharge

The kinetics of the destruction of diisopropyl methylphosphonate (DIMP) in corona discharge has been studied using a flow tubular coaxial wire dielectric barrier corona discharge reactor. The identification and quantitative determination of DIMP, its destruction intermediates, and phosphorus‐containing destruction products were performed using molecular beam mass spectrometry and gas chromatography/mass spectrometry. Active discharge power was varied in the range 0.01–5 W. The destruction products such as isopropyl methylphosphonate, methylphosphonic acid, and orthophosphoric acid were found on the reactor walls. The dependence of the extent of the destruction, D (D = 1 ? X / X₀, where X and X₀ are DIMP mole fractions at the outlet and the inlet of the reactor), on the specific energy deposition E_x (E_x = PF^?1 X₀^?1, where F is the carrier gas flow and P is the power dissipated in discharge reactor) was measured over the DIMP mole fraction range 60–500 ppm at the pressure of 1 bar and the temperature of 340 K. Over the range of the experimental conditions studied the destruction obeys the “pseudo‐first‐order” kinetic law: ln(1 ? D) = ?KE_x. Plausible mechanisms of the destruction are discussed. It was concluded that ion mechanism is the major one responsible for the destruction process. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 331–337, 2002     

Symmetrical dinuclear complexes with high DNA affinity based on [Ru(dpq)2(phen)]2+

Symmetrical homometallic dinuclear complexes of the type [(Ru(dpq)2)2(phen-SOS-phen)]4+, with a flexible 2-mercaptoethyl ether linker joining the two [Ru(dpq)2(phen)]2+-based sub-units, have DNA dissociation constants (Kd) in the nM range.     

The effect of a 3-benzyl group on the coordination chemistry of homoscorpionate ligands

New homoscorpionate ligands containing a 3-benzyl substituent, hydrotris(3-benzyl-5-methylpyrazol-1-yl)borate, Tp(Bn,Me), and hydrotris(3-benzyl-4-phenylpyrazol-1-yl)borate, Tp(Bn,4Ph), have been synthesized, and the dynamic behavior of a number of metal complexes was studied by NMR. Structures of the complexes Tl[Tp(Bn,Me)], 1, Tl[Tp(Bn,4Ph)], 2, Co[Tp(Bn,Me)][Tp(Np)], 3, Mo[Tp(Bn,Me)](CO)(2)NO, 4, Co[Tp(Bn,4Ph)][Tp], 5, and Mo[Tp(Bn,Me)](CO)(2)(eta(3)-methallyl), 6, were determined by X-ray crystallography. In the Tp(Bn,Me) ligand, the benzyl group is freely rotating and provides less steric hindrance to the coordinated metal than a neopentyl group, but steric hindrance is increased in the Tp(Bn,4Ph) ligand, where the rotation of the benzyl substituent is restricted by the 4-phenyl substituent.     

Wheel-shaped [Mn12] single-molecule magnets

The reaction of [Mn(12)O(12)(O(2)CCH(3))(16)(H(2)O)(4)].4H(2)O.2CH(3)COOH with n-methyldiethanol amine (H(2)mdea), n-ethyldiethanol amine (H(2)edea), or n-butyldiethanol amine (H(2)bdea) leads to the formation of wheel-shaped Mn(III)(6)Mn(II)(6) complexes with the general formula [Mn(12)(R)(O(2)CCH(3))(14)] (1, R = mdea; 2, R = edea; and 3, R = bdea). Complex 1 crystallizes in the triclinic space group P1, whereas complex 3 crystallizes in the monoclinic space group C(2/c). Complex 1a has the same molecular structure as complex 1 but crystallizes in the monoclinic space group P2(1/n). Complex 3a has the same molecular structure as complex 3 but crystallizes in the triclinic space group P1. Variable-temperature magnetic susceptibility data collected for complexes 1, 2, and 3 indicate that antiferromagnetic exchange interactions are present. The spin ground states of complexes 1, 2, and 3 were determined by fitting variable-field magnetization data collected in the 2-5 K temperature range. Fitting of these data yielded the spin ground-state parameters of S = 8, g = 2.0, and D = -0.47 cm(-1) for complex 1; S = 8, g = 2.0, and D = -0.49 cm(-1) for complex 2; and S = 8, g = 2, and D = -0.37 cm(-1) for complex 3. The ac magnetic susceptibility data were measured for complexes 1, 2, and 3 at temperatures between 1.8 and 10 K with a 3 G ac field oscillating in the range 50-1000 Hz. Slow kinetics of magnetization reversal relative to the frequency of the oscillating ac field were observed as frequency-dependent out-of-phase peaks for complexes 1, 2, and 3, and it can be concluded that these three complexes are single-molecule magnets.     

(Acetonitrile‐κN){2‐[bis­(2‐pyridylethyl)­amino]ethanol‐κ4N,N′,N′′,O}zinc(II) bis­(perchlorate) monohydrate

In the title compound, [Zn(C₂H₃N)(C₁₆H₂₁N₃O)](ClO₄)₂·H₂O, the Zn^II ion is coordinated by two pyridyl N atoms, one amine N atom, and an ethanol O atom from the N,N′,N′′,O‐tetra­dentate 2‐[bis­(2‐pyridylethyl)amino]­ethanol donor ligand. The fifth coordination site is filled by an acetonitrile N atom, and there is one solvent water mol­ecule in the asymmetric unit. The 2+ charge of the cationic portion of the complex is balanced by two perchlorate counter‐anions.     

Single-molecule magnets: high-field electron paramagnetic resonance evaluation of the single-ion zero-field interaction in a Zn(II)3Ni(II) complex

High-field electron paramagnetic resonance spectra were collected at several frequencies for a single crystal of [Zn3.91Ni0.09(hmp)4(dmb)4Cl4] (1), where dmb is 3,3-dimethyl-1-butanol and hmp- is the monoanion of 2-hydroxymethylpyridine. This crystal is isostructural to [Ni4(hmp)4(dmb)4Cl4] (2), which has been characterized to be a single-molecule magnet (SMM) with fast quantum tunneling of its magnetization (QTM). The single Ni(II) ion zero-field-splitting (zfs) parameters Di [= -5.30(5) cm(-1)] and Ei [= +/-1.20(2) cm(-1)] in the doped complex 1 were evaluated by rotation of a crystal in three planes. The easy-axes of magnetization associated with the single-ion zfs interactions were also found to be tilted 15 degrees away from the crystallographic c direction. This inclination provides a possible explanation for the fast QTM observed for complex 2. The single-ion zfs parameters are then related to the zfs parameters for the Ni4 molecule by irreducible tensor methods to give D = -0.69 cm(-1) for the S = 4 ground state of the SMM, where the axial zfs interaction is given by DS(Z)2.     

DNA sequencing with hydrophilic and hydrophobic polymers at elevated column temperatures

Read length in DNA sequencing by capillary electrophoresis at elevated temperatures is shown to be greatly affected by the extent of hydrophobicity of the polymer separation matrix. At column temperatures of up to 80 degrees C, hydrophilic linear polyacrylamide (LPA) provides superior read length and separation speed compared to poly(N,N-dimethylacrylamide) (PDMA) and a 70:30 copolymer of N,N-dimethylacrylamide and N,N-diethylacrylamide (PDEA30). DNA-polymer and polymer intramolecular interactions are presumed to be a major cause of band broadening and the subsequent loss of separation efficiency with the more hydrophobic polymers at higher column temperatures. With LPA, these interactions were reduced, and a read length of 1000 bases at an optimum temperature of 70 degrees -75 degrees C was achieved in less than 59 min. By comparison, PDMA produced a read length of roughly 800 bases at 50 degrees C, which was close to the read length attained in LPA at the same temperature; however, the migration time was approximately 20% longer, mainly because of the higher polymer concentration required. At 60 degrees C, the maximum read length was 850 bases for PDMA, while at higher temperatures, read lengths for this polymer were substantially lower. With the copolymer DEA30, read length was 650 bases at the optimum temperature of 50 degrees C. Molecular masses of these polymers were determined by tandem gel permeation chromatography-multiangle laser light scattering method (GPC-MALLS). The results indicate that for long read, rapid DNA sequencing and analysis, hydrophilic polymers such as LPA provide the best overall performance.     

The molecular structure and the puckering potential function of silacyclobutane as determined by gas electron diffraction and relaxation constraints from ab initio calculations

Gas electron diffraction is applied to determine the geometric parameters of the silacyclobutane molecule using a dynamic model where the ring puckering was treated as a large amplitude motion. The structural parameters and the parameters of the potential function were refined taking into account the relaxation of the molecular geometry estimated from ab initio calculations at the MP2/6-311+G(d, p) level of theory. The potential function has been described as V() = V₀[(/_e)² − 1]² with the following parameters V₀ = 0.82 ± 0.60 kcal/mol and _e = 33.5 ± 2.7°, where is a puckering angle of the ring.

The geometric parameters at the minimum V() (r_a in Å, in degrees and uncertainties given as three times the standard deviations including a scale error) are: r(Si–H_ax) = 1.467(96), r(Si–H_eq) = 1.468(96), r(Si–C) = 1.885(2), r(C–C) = 1.571(3), r(C–H) = 1.100(3), CSiC = 77.2(9), HSiH = 108.3, SiCH_eq = 123.5(16), SiCH_ax = 111.9(16), CC₅H_eq = 118.4(24), CC₅H_ax = 112.3(24), HC₃H = 107.7, δ(HSiH) = 6.6, δ(HC₃H) = 7.0, where the tilts δ, HSiH, and HC₃H are estimated from ab initio constraints. The structural parameters are compared with those obtained for related compounds.     

Electron diffraction study on the molecular structure of hexamethylcyclotrisilazane, [(CH3)2SiNH]3

A gas electron diffraction study yielded the following geometrical parameters for hexamethylcyclotrisilazane: r(Si-N) = 1.728 ± 0.004 Å, r(Si-C) = 1.871 ± 0.004 Å, r(C-H) = 1.124 ± 0.007 Å, ∠N-Si-N = 108.4 ± 1.0°, ∠Si-N-Si = 126.8 ± 0.8°, ∠C-Si-C = 108.9 ± 2.3°, ∠H-C-H = 111.6 ± 0.9°. The (SiN)₃ ring was found to be puckered but the deviation from planarity is relatively small. Details of the ring shape could not be determined. The degree of ring puckering in six-membered rings with alternating atoms can be roughly predicted from the bond angles in analogous non-cyclic molecules.