Katherine N. Robertson

CRYSTAL STRUCTURES AND PHYSICO-CHEMICAL PROPERTIES OF A SERIES OF RU2(O2CCH3)4L2 (PF6) ADDUCTS (L = H2O, DMF, DMSO)

Abstract The reaction of Ru 2 (O 2 CCH 3 ) 4 Cl with water in the presence of Ag 2 SO 4 and NH 4 PF 6 leads to the formation of [Ru 2 (O 2 CCH 3 ) 4 (H 2 O) 2 ](PF 6 ) (1). The subsequent reaction of complex 1 with dimethylformamide (DMF) and dimethylsulfoxide (DMSO) results in the formation of [Ru 2 (O 2 CCH 3 ) 4 (DMF) 2 ](PF 6 ) ( 2 ); [Ru 2 (O 2 CCH 3 ) 4 (DMF) 2 ](PF 6 )·DMF ( 2a ) and [Ru 2 (O 2 CCH 3 ) 4 (DMSO) 2 ](PF 6 ) ( 3 ). All complexes were characterized using single crystal X-ray crystallography, IR and UV-Vis spectroscopy, cyclic voltammetry and magnetic susceptibility. The crystallographic data for [Ru 2 (O 2 CCH 3 ) 4 (H 2 O) 2 ](PF 6 )·3H 2 O ( 1a ) are as follows: monoclinic space group C 2/ c with unit cell dimensions a = 19.552(2), b = 12.853(2), c = 8.487(2) A , β = 93.02(2)°, V = 2129.6(6) A 3 , Z = 4 . The structure was refined to R = 0.0244 ( R w = 0.266) with 1165 reflections having I > 3 σ ( I ). The RuRu distance is 2.2648(9) A; Ru distances are 2.023(4), 2.039(3), 2.018(4) and 2.026(3) A; Ru  O ( axial ) = 2.279(4) A . The relevant data for 2 are: orthorhombic, space group P 2 1 2 1 2 1 with unit cell dimensions a = 11.704(2), b = 28.452(10), c = 8.415(3) A , V = 2802(2) A 3 , Z = 4 . The structure was refined to R = 0.0597 ( wR 2 = 0.1520) with 909 reflections having I >2 σ ( I ). The RuRu distance is 2.262(3) A; RuO distances are 1.999(14), 2.003(13), 2.004(13) and 2.009(13) A; the RuO(axial) distances are both 2.22(2) A. The pertinent crystal data for 2a are: monoclinic, space group P 2 1 / c with unit cell dimensions a = 8.382(4), b = 11.918(3), c = 30.715(5) A , β = 96.84(3)°, V = 3046(1) A 3 , Z = 4 . The structure was refined to R = 0.0558 ( wR 2 = 0.1388) with 1317 reflections having I >2 σ ( I ). The RuRu distance is 2.265(2) A; RuO distances are 2.021(13), 2.052(13) and 2.023(14) A; the RuO(axial) distances are both 2.229(14) A. The data for 3 are: triclinic, space group P 1 with unit cell dimensions a = 11.45(1), b = 14.103(4), c = 8.303(3) A , α = 90.46(2), β = 110.15(4), γ = 78.93(4)°, V = 1232(1) A 3 , Z = 2 . The structure was refined to R = 0.0301 ( R w = 0.0382) with 2578 reflections having I >3 σ ( I ). The RuRu bond distances are 2.274(1) and 2.268(1) A; RuO distances range from 2.017(5) to 2.035(5) A; the RuO(axial) distances are 2.240(5) and 2.243(5) A. Increasing the donor number of the axial ligand manifests only very small changes in RuRu bond length, reduction potential and π ∗ ( Ru 2 ) → π( RuO, Ru 2 ) transition energy and no changes in μ eff implying only minor perturbation of σ ∗ and π ∗ orbital energies.

A simple complex on the verge of breakdown: Isolation of the elusive cyanoformate ion

Cyanide Hitches a Ride Cyanide is a by-product of the biosynthesis of ethylene in plants and it has been somewhat puzzling how the ion is safely removed before it can shut down enzymatic pathways by coordination to catalytic iron centers. A proposed mechanism has implicated the cyanoformate ion—essentially, a weak adduct of cyanide and carbon dioxide—as the initial product, although its lifetime was uncertain. Murphy et al. (p. 75; see the Perspective by Alabugin and Mohamed) crystallized this previously elusive adduct and found that its solution-phase stability varies inversely with the dielectric properties of the medium. The results bolster a picture in which the adduct shuttles the cyanide away from the hydrophobic confines of the enzyme before releasing the cyanide into the more polar aqueous surroundings. Characterization of a cyanide–carbon dioxide adduct bolsters its possible role in protecting a plant enzyme from cyanide inhibition. [Also see Perspective by Alabugin and Mohamed] Why does cyanide not react destructively with the proximal iron center at the active site of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase, an enzyme central to the biosynthesis of ethylene in plants? It has long been postulated that the cyanoformate anion, [NCCO2]–, forms and then decomposes to carbon dioxide and cyanide during this process. We have now isolated and crystallographically characterized this elusive anion as its tetraphenylphosphonium salt. Theoretical calculations show that cyanoformate has a very weak C–C bond and that it is thermodynamically stable only in low dielectric media. Solution stability studies have substantiated the latter result. We propose that cyanoformate shuttles the potentially toxic cyanide away from the low dielectric active site of ACC oxidase before breaking down in the higher dielectric medium of the cell.

Definitive identification of lead(II)-amino acid adducts and the solid state structure of a lead-valine complex

Electrospray ionization mass spectra of lead(II) nitrate-amino acid mixtures enable unequivocal identification of lead complexes for each of the essential amino acids and a valine complex is reported as the first crystallographically characterized lead-amino acid complex.

Bond length and the electron density at the bond critical point: X--X, Z--Z, and C--Z bonds (X = Li-F, Z = Na-Cl).

The aim was to investigate the relationship between the bond length and the electron density at the bond critical point in homonuclear XX and ZZ and heteronuclear CZ bonds (X = Li‐F, Z = Na‐Cl). The d,ρc pairs were obtained from 472 target bonds in DFT‐optimized (B3LYP/6‐311+G(d,p)) small molecular species. These species were selected arbitrarily but with a view to maximize the range widths WR for each atom combination. It was found that (i) with one clear exception, the d(A − A) means (A = X or Z) correlate linearly with the bond lengths d(A2) of the respective diatomic molecules; (ii) the d(A − A) means correlate parabolically with n, the formal number of valence electrons in the atoms of the bond; and (iii) with increasing sample size N the ratio WR(ρc)/WR(d) appears to converge toward a representation f [WR(ρc)/WR(d)]N→∞ characteristic of A. Detailed analysis of the d,ρc relationship has shown that by and large simple power regression accounts best for the DFT data. The regression coefficients of d = aρ  c−b and ρc = αd−β (b, β > 0) vary with n in a seemingly irregular manner but one that is consistent with simple chemical notions. The d(A2) can be approximated in terms of multilinear MO electron occupancies.

Synthesis, structure and electrochemistry of nitrogen base adducts of tetraacetatodiruthenium(II,III): dependence of redox potential and Ru–Ru bond length on axial ligand donor strength

Diadduct complexes of the mixed-valent form of diruthenium tetraacetate, [Ru-2(mu-O2CCH3)(4)L-2](PF6), with L = N-heterocyclic axial ligands quinuclidine (quin) (1), 4-methylpyridine (4-Mepy) (2), pyridine (py) (3), 4-cyanopyridine (4-CNpy) (4), 3-cyanopyridine (3-CNpy) (5) and 4-phenylpyridine (4-Phpy) (6) have been synthesized and all but 5 were characterized by X-ray crystallography to study the effect of the variation of the donor number (DN) of L on the Ru-Ru and Ru-L-ax bond lengths, the magnetic moment, the electronic spectral properties and the redox potential. When data from previous studies on O-donor adducts was also included a DN range of 18-61 could be established. Over this range the Ru-Ru bond length increases slightly from 2.265(1) to 2.2917(6) Angstrom as the donor number is increased from 18 (in [Ru-2(mu-O2CCH3)(4)(H2O)(2)](PF6)) to 61 in 1. UV - Vis measurements show a very slight increase in energy of the pi(Ru-O, Ru-2)-->pi*(Ru-2) transition, however, room temperature magnetic susceptibility measurements show no change in the magnetic moment over the same range of donor numbers. Electrochemical measurements in 1,2-dichloroethane of the Ru-2(4+/5+) redox couple show a decrease in the E-1/2 of 292 mV on going from complex 5 (weakest N-donor) to complex 1 (strongest N-donor). The E-1/2 range is over 400 mV when the unligated [Ru-2(mu-O2C(CH2)(6)CH3)(4)] complex is included (DN = 1 for dichloromethane). The variation of axial ligand base strength does not effect, the near-degeneracy of the (pi*delta*)(3) HOMO or the pi-->pi* energy gap, however, the actual (pi*delta*)(3) HOMO energy varies significantly and increases as the basicity of the axial ligand increases allowing selective tuning of the redox potential

A novel, organic-additive-free synthesis of nanometer-sized NaX crystals

Ultra-fine NaX zeolite crystals of dimensions ca. 20–100 nm have been synthesized with a novel, efficient, organic-additive-free hydrothermal approach.

Configurations and conformations of glycosyl sulfoxides

X-ray crystallographic studies of two axial glycosyl sulfoxides having RS configurations (derivatives of phenyl 2-azido-2-deoxy-1-thio-α-d-galactopyranoside S-oxide) show that they adopt anti confo...

Synthesis and structure of the first sulfur-donor adduct of a diruthenium tetracarboxylate

Abstract The first sulfur-donor adduct of a diruthenium tetracarboxylate, [Ru 2 ( -O 2 CCH 3 ) 4 (THT) 2 ]PF 6 ( 1 ), where THT=tetrahydroth-iophene, has been synthesized and characterized by X-ray diffraction, IR and UV–Vis spectroscopy, magnetic susceptibility andelectrochemistry. Complex 1 displays a typical Ru Ru bond length of 2.285(4) A but a very long Ru S axial bond of 2.627(13)A. The redox potential for the [Ru 2 ( -O 2 CCH 3 ) 4 (THT) 2 ] +/0 couple is −322 mV (vs. Fc/Fc + ) which is comparable to othermoderately strong Lewis base adducts. Axial ligand binding is driven by -donation with little -backdonation from the metalcenters.

The synthesis of cis-Re(O,O′-No2)(CO)2(PPh3)2 containing the unusual O,O′-chelating nitrite ligand and its reaction with CO. Evidence for a rhenium-nitrogen interaction

Abstract The synthesis of the bidentate nitrite complex, Re( O,O− -NO 2 )(Co) 2 (PPh 3 ) 2 , from [Re(CH 3 CN) 2 (CO) 2 (PPh 3 ) 2 ]ClO 4 is reported. The possibility of a ReN interaction in Re( O,O− NO 2 )(CO) 2 )(PPh 3 ) 2 ) is indicated by the derivative chemistry of the complex with CO, p -tolylisocyanide and HCl. A superior, high yield route to ReH(CO) 2 (PPh 3 ) 3 is also described.

Mono‐ and Bis(imidazolidinium ethynyl) Cations and Reduction of the Latter To Give an Extended Bis‐1,4‐([3]Cumulene)‐p‐carboquinoid System

An extended π-system containing two [3]cumulene fragments separated by a p-carboquinoid and stabilized by two capping N-heterocyclic carbenes (NHCs) has been prepared. Mono- and bis(imidazolidinium ethynyl) cations have also been synthesized from the reaction of an NHC with phenylethynyl bromide or 1,4-bis(bromoethynyl)benzene. Cyclic voltammetry coupled with synthetic and structural studies showed that the dication is readily reduced to a neutral, singlet bis-1,4-([3]cumulene)-p-carboquinoid as a result of the π-accepting properties of the capping NHCs.