Cyanide Carbon Research Articles

Electronic Structure of the Acetonitrile and Acetonitrile Dimer Anions: A Topological Investigation

Acetonitrile molecules are known for their intriguing ability to accommodate an excess electron in either a diffuse dipole-bound orbital, away from the valence electrons, or in its valence orbitals, depending on the environment. In this work, we report a computational investigation of the monomer and dimer acetonitrile anions, with the main goal of gaining further insight into the unusual electronic structure of these species. To this end, the topology of the electron density distribution has been examined in detail with the quantum theory of atoms in molecules (AIM). The excess electron is found to affect the topology of the electron density very differently for two dipole-bound-electron isomers of the acetonitrile dimer anion: for the head-to-tail isomer, the electron density simply decays away from the atomic nuclei, and the presence of the excess electron only manifests itself in the Laplacian of the electron density as a very diffuse region of "dipole-bound" charge concentration; in contrast, for the "solvated-electron" head-to-head isomer, a maximum of electron density without a corresponding atomic nucleus is observed, which topologically corresponds to a pseudo-atom of electron density. The acetonitrile dimer appears to be the smallest solvent cluster anion to exhibit such a non-nuclear attractor due to the presence of a solvated electron. Although the "solvated-electron" isomer is thermodynamically less stable than the head-to-tail isomer at 0 K, its floppy nature leads to a higher vibrational entropy that makes it the most stable acetonitrile dimer, anionic or neutral, above 150 K. As for the acetonitrile dimer anion with a valence-bound electron, its structure is characterized by acetonitrile molecules connected to each other at the cyanide carbon atoms; the AIM analysis reveals that, although this C-C bond is relatively weak, with an estimated bond order of 0.6, it possesses genuine covalent character and is not a "pseudo-bond" as previously speculated. We also report the first multireference electronic structure calculations of the valence-bound-electron acetonitrile monomer and dimer anions, the highest-level calculations of these species to date. The acetonitrile radical anion is unstable in the gas phase and is topologically characterized by a radical-like nonbonded charge concentration located at the cyanide carbon atom. Based on the results of the AIM analysis, the previously proposed resonance description of the valence-bound-electron acetonitrile anion is refined, and a new resonance description of the dimer anion is proposed. Overall, this work demonstrates the rich topological variety of the excess electron interacting with acetonitrile molecules, which manifests itself as charge concentrations, pseudo-atoms, and covalent bonds.

Cyano-Bridged FeIII2CuII3and FeIII4NiII4Complexes: Syntheses, Structures, and Magnetic Properties

Two tricyanometallate precursors, (Bu4N)[(Tp4Bo)Fe(CN)3].H2O.2MeCN (1) and (Bu4N)[(pzTp)Fe(CN)3] (2) [Bu4N+ = tetrabutylammonium cation; Tp4Bo = tris(indazolyl)hydroborate; pzTp = tetrakis(pyrazolyl)borate], with a low-spin FeIII center have been synthesized and characterized. The reactions of 1 or 2 with [Cu(Me3tacn)(H2O)2](ClO4)2 (Me3tacn = N,N',N' '-trimethyl-1,4,7-triazacyclononane) afford two pentanuclear cyano-bridged clusters, [(Tp4Bo)2(Me3tacn)3Cu3Fe2(CN)6](ClO4)4.5H2O (3) and [(pzTp)2(Me3tacn)3Cu3Fe2(CN)6](ClO4)4.4H2O (4), respectively. Assembly reactions between 2 and [Ni(phen)(CH3OH)4](ClO4)2 (phen = 1,10-phenanthroline) or Zn(OAc)2.2H2O afford a molecular box [(pzTp)4(phen)4Ni4Fe4(CH3OH)4(CN)12](ClO4)4.4H2O (5) and a rectangular cluster [(pzTp)2Zn2Fe2(OAc)2(H2O)2(CN)6] (6). Their molecular structures were determined by single-crystal X-ray diffraction. In complexes 1 and 2, the central FeIII ions are coordinated by three cyanide carbon atoms and three nitrogen atoms of Tp4Bo- or pzTp-. Both complexes 3 and 4 show a trigonal-bipyramidal geometry, in which [(L)Fe(CN)3]- units occupy the apical positions and are linked through cyanide to [Cu(Me3tacn)]2+ units situated in the equatorial plane. Complex 5 possesses a cubic arrangement of eight metal irons linked through edge-spanning cyanide bridges, while complex 6 shows Zn2Fe2(CN)4 rectangular structure, in which FeIII and ZnII ions are alternately bridged by the cyanide groups. Intramolecular ferromagnetic couplings are observed for complexes 3-5, and they have S = 5/2, 5/2, and 6 ground states and appreciable magnetic anisotropies with negative D values equal to -0.49, -2.39, and -0.39 cm-1, respectively.

Crystal Structures of Chloroperoxidase with Its Bound Substrates and Complexed with Formate, Acetate, and Nitrate

Chloroperoxidase (CPO) is a heme-thiolate enzyme that catalyzes hydrogen peroxide-dependent halogenation reactions. Structural data on substrate binding have not been available so far. CPO was therefore crystallized in the presence of iodide or bromide. One halide binding site was identified at the surface near a narrow channel that connects the surface with the heme. Two other halide binding sites were identified within and at the other end of this channel. Together, these sites suggest a pathway for access of halide anions to the active site. The structure of CPO complexed with its natural substrate cyclopentanedione was determined at a resolution of 1.8 A. This is the first example of a CPO structure with a bound organic substrate. In addition, structures of CPO bound with nitrate, acetate, and formate and of a ternary complex with dimethylsulfoxide (Me2SO) and cyanide were determined. These structures have implications for the mechanism of compound I formation. Before binding to the heme, the incoming hydrogen peroxide first interacts with Glu-183. The deprotonated Glu-183 abstracts a proton from hydrogen peroxide. The hydroperoxo-anion then binds at the heme, yielding compound 0. Glu-183 protonates the distal oxygen of compound 0, water is released, and compound I is formed.

Cyanide-bridged molecular squares with ferromagnetically coupled dpi, dsigma, and ppi spin system.

Cyanide-bridged molecular squares of [Fe(II)(2)Cu(II)(2)(mu-CN)(4)(dmbpy)(4)(impy)(2)](ClO(4))(4).4CH(3)OH.C(6)H(6) (1) and of [Fe(III)(2)Cu(II)(2)(mu-CN)(4)(dmbpy)(4)(impy)(2)](ClO(4))(6).4CH(3)OH.4H(2)O (2) (dmbpy = 4,4'-dimethyl-2,2'-bipyridine; impy = 2-(2-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxy) were prepared. In the squares of 1 and 2, the Fe(II/III) (low spin) and Cu(II) ions are alternately bridged by the cyanide groups, in which the cyanide carbon atoms coordinated to the Fe(II) ions and Cu(II) ions are coordinated by imino nitroxide. Magnetic susceptibility measurements for 1 and 2 revealed that the Cu(II) ion and imino nitroxide are ferromagnetically coupled with a fairly strong coupling constant (J(Cu-radical) > 300 K) and act as triplet species. In 1 the Cu(II)-radical moieties are magnetically separated by the Fe(II) ions. In the square of 2, dpi (Fe(III)), dsigma (Cu(II)), and ppi (imino nitroxide) spins are alternately assembled, and this situation allowed the square to have an S = 3 spin ground state. The exchange coupling constant of Fe(III) and the Cu(II)-radical moiety in 2 was estimated to be J = 4.9 cm(-1) (H = -2JSigmaS(Fe).S(Cu-radical)).

The First Precise Molecular Structure of a Monomeric Transition Metal Cyanide, Copper(I) Cyanide

Copper(I) cyanide is an important reagent in organic, organometallic, and supramolecular chemistry because of both the copper center and the versatile cyanide ligand. Solid-phase CuCN and many of its derivatives show oligomeric or polymeric structures, a trait shared by other metal cyanides. Often, it is difficult to specify the orientation of the cyano ligand in an X-ray structure. Here the first preparation and precise structure of a monomeric transition metal cyanide is reported. Gas-phase reaction between copper vapor and cyanogen (NCCN) clearly gives CuCN (not CuNC). The precise structure of CuCN so produced is determined by millimeter/submillimeter-wave spectroscopy. Because of the highly efficient synthesis and the presence of significant amounts of two copper isotopes, such strong signals were seen that natural-abundance materials allowed observation of transitions for the four isotopomers (63)Cu(12)C(14)N, (65)Cu(12)C(14)N, (63)Cu(13)C(14)N, and (63)Cu(12)C(15)N and the determination of r(o), r(s), and r(m)((2)) structures. All data unequivocally show a linear geometry and that the carbon of cyanide is bound to copper with a Cu-C distance of 1.82962(4) A in the r(m)((2)) structure, which is likely to be closest to the equilibrium geometry.

Syntheses, structure and spectroscopic characterization of fac- and mer-Co(aepn)(CN) 3 and of their 13CN analogues [aepn= N-(2-aminoethyl)-1,3-propanediamine

Both facial ( 1) and meridional ( 3) isomers of Co(aepn)(CN) 3 [aepn= N-(2-aminoethyl)-1,3-propanediamine] and their 13CN analogues (facial 2 and meridional 4) have been prepared by two different synthetic approaches. 1 crystallizes in a monoclinic space group, P2 1/ c, and has one long and two short CN bonds. Meanwhile 3 crystallizes with a water of crystallization in the same space group ( P2 1/ n) and has one short and two long CN bonds. The 13C NMR spectrum of 4 shows three well-resolved resonances ( δ=143.53, 142.14, 132.85) for the three mer cyanide carbon atoms. In contrast, 3 has a single broad resonance in the range of δ=120–140, suggesting the presence of a dynamic process that is thought to be a trigonal twist of the three fac cyanide groups. According to the analyses of IR and Raman spectra, the Co(CN) 3 moiety of both isomers appears to have approximate C s molecular symmetry resulting in three IR- and Raman-active ν(CN) modes. Individual assignments of the vibrational peaks in the ν(CN) region have been confirmed by Raman band polarization measurements and 13CN isotope shifts. The stretching and bending modes of the metal-cyano groups in the low-frequency region (<600 cm −1) have also been analyzed.

Synthesis, Structure, and Solution NMR Studies of Cyanide-Copper(II) and Cyanide-Bridged Iron(III)-Copper(II) Complexes.

A range of small molecules, such as cyanide, are known to bind and/or inhibit the active site of the heme-copper oxidase enzymes. As such, model studies are aimed at elucidating ligand binding modes and their subsequent impact on spectroscopic properties of derived complexes. We describe here the isolation and characterization of two compounds containing the Fe-CN-Cu moiety, [(py)(F(8)-TPP)Fe(III)-CN-Cu(II)(TMPA)](2+) (5) and [(F(8)-TPP)Fe(III)-(CN)(2)-{Cu(II)(TMPA)}(2)](3+) (6) [py = pyridine, TMPA = tris(2-pyridylmethyl)amine, and (F(8)-TPP) = tetrakis(2,6-difluorophenyl)porphyrinate(2-)]. [Cu(II)(TMPA)(CH(3)CN)](ClO(4))(2) and [(py)(F(8)-TPP)Fe(III)(CN)] (3) react to yield 5, while 6 is formed by combination of [Cu(II)(TMPA)(CN)]PF(6) (2-(PF(6))) and [(F(8)-TPP)Fe(III)(PF(6))] (4). Complex 2-(PF(6)) crystallizes in the orthorhombic space group Iba2 with a = 17.2269(5) Å, b = 17.3143(4) Å, and c = 14.4971(4) Å, Z = 8, complex (5-(Sb/P)F(6))(1.5)(ClO(4))(0.5) was obtained in the orthorhombic space group P222 with a = 17.9541(2) Å, b = 20.5359(1) Å, and c = 21.2023(2) Å, Z = 4, and 6-(PF(6))(3) crystallized in the monoclinic space group P2(1)/c with a = 15.318(4) Å, b = 33.921(2) Å, and c = 19.649(6) Å, beta = 109.69(2) degrees, and Z = 4. Compound 5 possesses a low-spin iron(III) center, bridged via cyanide to copper. The iron-cyanide vector deviates slightly from linearity (174.6(5) degrees ). The copper(II) ion is five-coordinated by the TMPA N-donor atoms and the cyanide carbon atom. The Cu(TMPA) moiety is bent with an angle of 163.8(5) degrees around the cyanide-copper vector. Compound 6 possesses a low-spin iron(III) atom axially coordinated by two cyanide ligands capped on either side by trigonally coordinated [Cu(TMPA)] moieties. The [Cu(1)(TMPA)] unit is twisted somewhat ( angleCu1-N&tbd1;C = 168 degrees ), whereas the [Cu(2)(TMPA)] unit is coordinated in a nearly linear fashion with respect to the cyanide-iron vector ( angleCu2-N&tbd1;C4 = 175 degrees ). (1)H and (2)H NMR spectroscopy on 5 and 6 confirmed the low-spin nature of these iron complexes (pyrrole resonance found at -11.1 and -8 ppm, respectively). The NMR data as well as observed solution magnetic moment (&mgr;(B) = 2.7 for 5; &mgr;(B) = 3.4 for 6) suggest ferromagnetic coupling between the paramagnetic metal ions. This gives rise to an enhancement of the electronic relaxation rate for Cu(II) in both 5 and 6 allowing for the observation of the sharp and downfield shifted TMPA ligand proton signals.

Change in Electron Configuration of Ferric Ion in Bis(cyanide)(meso-tetraalkylporphyrinatoiron(III)), [Fe(TRP)(CN)2]-, Caused by the Nonplanarity of the Porphyrin Ring

The synthesis and characterization of a series of bis(cyanide)(meso-tetraalkylporphyrinatoiron(III)), [Fe(TRP)(CN)2]- where R is H, Me, Et, and iPr, are reported. The 1H NMR spectrum of the unsubstituted [Fe(THP)(CN)2]- shows a pyrrole signal at δ = −23.19 ppm (−25 °C) in CD2Cl2, which is quite typical as a low spin ferric complex. As the bulkiness of the meso substituent increases, the pyrrole signal moves to lower magnetic field; 0.34, −2.26, and 11.94 ppm for [Fe(TMeP)(CN)2]-, [Fe(TEtP)(CN)2]-, and [Fe(TiPrP)(CN)2]-, respectively. Corresponding to the pyrrole proton signal, the cyanide carbon signal also exhibits a large downfield shift. The difference in chemical shifts between [Fe(THP)(CN)2]- and [Fe(TiPrP)(CN)2]- reaches as much as 1443 ppm at −25 °C. The substituent dependent phenomena are also observed in EPR spectra taken in frozen CH2Cl2 solution at 4.2 K. While the unsubstituted complex gives a so called large gmax type signal at 3.65, the alkyl substituted complexes exhibit axial type spectra; the EPR parameters for [Fe(TiPrP)(CN)2]- are g⊥ = 2.43 and g∥ = 1.73. These results clearly indicate that the electronic ground state changes from the usual (dxy)2(dxz, dyz)3 to the unusual (dxz, dyz)4(dxy)1 as the substituent becomes bulkier. Analysis of the EPR g values reveals that the orbital of the unpaired electron has more than 90% dxy character in the alkyl substituted complexes. The unusual electron configuration is ascribed to the destabilization of dxy orbital and/or stabilization of dxz and dyz orbitals caused by the S4 ruffled structure of the alkyl substituted porphyrin ring. Thus, in a strongly ruffled low spin complex such as [Fe(TiPrP)(L)2]±, electron configuration of iron is presented by (dxz, dyz)4(dxy)1 regardless of the kind and basicity of the axial ligand (L). In fact, low spin bis(pyridine) complex [Fe(TiPrP)(Py)2]+ gives a pyrrole signal at quite a low field, δ = +16.4 ppm at −87 °C, which is actually the lowest pyrrole signal ever reported for the low spin ferric porphyrin complexes. Correspondingly, the EPR spectrum taken at 77 K showed a clear axial type spectrum, g⊥ = 2.46 and g∥ = 1.59. In every case examined, (dxz,dyz)4(dxy)1 ground state is more or less stabilized by the addition of methanol as exemplified by the further downfield shift of the pyrrole proton and cyanide carbon signals together with the smaller EPR g⊥ values. The methanol effect is explained in terms of the stabilization of dxz and dyz relative to dxy due to the hydrogen bond formation between coordinated cyanide and methanol.

Carbon-13 EPR Hyperfine Interaction in the Complex [Rh(CN)6]4−in a KCl Host Lattice

The hyperfine interaction with13C in nonenriched [Rh(CN)6]4−, in a KCl host lattice at 7 K, is measured by continuous-wave X- and Q-band electron paramagnetic resonance, allowing, for the first time, a comparative study of spin densities on the carbon of the axial cyanide in this complex and in the similar [Co(CN)6]4−complex. From the experimental data corrected for dipolar interactions,Aiso= 79.80 × 10−4cm−1andAanis= 0.76 × 10−4cm−1.

Synthesis, characterisation and reactivity of hydrazine complexes of iron(II)

Hydrazine complexes [Fe(R1NHNH2)(R2CN)L4][BPh4]2 1–3 and [FeH(R1NHNH2)L4]BPh4 4 [R1 = H, Me, Ph, 4-MeC6H4, 4-ClC6H4, 4-O2NC6H4 or Me2NNH2; R2 = 4-MeC6H4, Me or Ph; L = P(OEt)3, P(OMe)3 or PPh(OEt)2] were prepared by reacting nitrile complexes [Fe(R2CN)2L4][BPh4]2 and [FeH(R2CN)L4]BPh4 with an excess of the appropriate hydrazine. Their formulation and geometry in solution were established by infrared and 1H and 31P NMR spectroscopy. Amidrazone derivatives [Fe{η2-NHC(R2)NR1NH2}L4][BPh4]2 [R2 = 4-MeC6H4, Me or Ph; R1 = H or Me; L = P(OEt)3 or P(OMe)3] were obtained by allowing nitrilehydrazine complexes to react in solution and their formation, involving a nucleophilic attack of the hydrazine on the cyanide carbon atom of the R2CN ligand, is also discussed. Reaction of the arylhydrazine complexes 1–4 with Pb(O2CMe)4 at –30 °C in CH2Cl2 resulted in selective oxidation of the arylhydrazine ligand affording the aryldiazene [Fe(R1NNH)(R2CN)L4][BPh4]2 and [FeH(R1NNH)L4]BPh4 10 [R1 = aryl; L = P(OEt)3 or P(OMe)3] derivatives. Treatment of the arylhydrazine [Fe(R1NHNH2)(R2CN){P(OEt)3}4][BPh4]2 1 (R1 = Ph or 4-MeC6H4) with an excess of NEt3 resulted in a complicated reaction giving the five-co-ordinate aryldiazenido derivatives [Fe(R1N2){P(OEt)3}4]BPh4.

The effects of interplay between quadrupolar, dipolar and shielding tensors on magic-angle spinning NMR spectra: shapes of spinning sidebands

The shapes of spinning sidebands for 13C magic-angle spinning spectra of solids affected by residual dipolar splittings to 14N are found to be spinning-speed dependent. Simple theory for the case of co-axial tensors indicates that centreband splittings at low spinning speeds yield values of xD (x and D are quadrupolar and dipolar coupling constants respectively) directly. The case of the cyanide carbon resonances for the coordination polymer [ᵵ(CH3)3Pb∼4Ru(CN)6]∞ is considered in detail. Computer simulations of the sideband bandshapes fit the experimental results well. The quadrupole coupling constants for the three cyanide nitrogen sites lie in the range -1·9 to -2·5 MHz. The shielding anisotropy for the cyanide carbon giving the highest-frequency resonance is found to be Δσ = ± 350 ppm.

Microstructure of vinylidene cyanide copolymers with linear-chain fatty acid vinyl esters

The microstructure of vinylidene cyanide (VDCN) copolymers with linear-chain fatty acid vinyl esters, vinyl propionate, vinyl butyrate and vinyl hexanoate, was studied by 67.9 MHz 13C n.m.r. spectroscopy. It was found that the compositional sequence distributions obtained from the analysis of the cyanide carbon (VDCN-centred) pentad and the methine carbon (comonomer-centred) triad resonances of all copolymers were highly alternative. Tactic structures in the alternating sequence were almost completely atactic. The microstructures of all copolymers were not largely different from each other. So, we suppose that possible origins of piezoelectricity observed for vinylidene cyanide copolymers should be found in other factors than the microstructure.

Molecular structures of cyano(methyl)silane and cyanodi(methyl)silane in the gas phase, determined by electron diffraction, and vibrational spectra of cyano(methyl)silane

The molecular structures of monomethylsilyl cyanide and dimethylsilyl cyanide in the gas phase have been determined by electron diffraction. The molecules have bond lengths (pm) and angles (degrees): MeSiH 2CN: r(SiCN) 184.7(9), r(SiCH) 186.6(9), r(SiH) 147.9(9), r(CH) 108.5(7), r(CN) 116.7(3), ∠HCH 105.4(20), ∠CSiC(N) 109.5(15); Me 2SiHCN: r(SiCN) 186.7(9), r(SiCH 3) 185.7(5), r(SiH) 151 fixed, r(CH) 110.0(7), r(CN) 116.4(7), ∠HCH 110.2(7), ∠CSiC(N) 111.4(15), ∠CSiC 103.2(20), ∠SiCN 170(4). There are apparent deviations from linearity at the cyanide carbon in each case, but these are believed to be shrinkage effects. A vibrational assignment is proposed for CH 3SiH 2CN.

Metal-catalysed addition of β-dicarbony compounds to the nitrile carbon of benzoyl cyanide. Synthesis of 1-amino-1-benzoyl-2,2-diacylethenes

The complex [Ni(acac)2](Hacac pentane-2,4-dione) selectively catalyses addition of the intercarbonylic carbon atom of β-diketones to the cyano group of benzoyl cyanide, whereas usual basic organic catalysts lead to attack on the carbonyl carbon atom with displacement of the CN group.

Excretion of 14C-labeled cyanide in rats exposed to chronic intake of potassium cyanide

The excretion of an acute dose of 14C-labeled cyanide in urine, feces, and expired air was studied in rats exposed to daily intake of unlabeled KCN in the diet for 6 weeks. Urinary excretion was the main route of elimination of cyanide carbon in these rats, accounting for 83% of the total excreted radioactivity in 12 hr and 89% of the total excreted radioactivity in 24 hr. The major excretion metabolite of cyanide in urine was thiocyanate, and this metabolite accounted for 71 and 79% of the total urinary activity in 12 hr and 24 hr, respectively. The mean total activity excreted in expired air after 12 hr was only 4%, and this value did not change after 24 hr. Of the total activity in expired air in 24 hr, 90% was present as carbon dioxide and 9% as cyanide. When these results were compared with those observed for control rats, it was clear that the mode of elimination of cyanide carbon in both urine and breath was not altered by the chronic intake of cyanide.

Cyanide production by Pseudomonas fluorescens and Pseudomonas aeruginosa.

Of 200 water isolates screened, five strains of Pseudomonas fluorescens and one strain of Pseudomonas aeruginosa were cyanogenic. Maximum cyanogenesis by two strains of P. fluorescens in a defined growth medium occurred at 25 to 30 degrees C over a pH range of 6.6 to 8.9. Cyanide production per cell was optimum at 300 mM phosphate. A linear relationship was observed between cyanogenesis and the log of iron concentration over a range of 3 to 300 microM. The maximum rate of cyanide production occurred during the transition from exponential to stationary growth phase. Radioactive tracer experiments with [1-14C]glycine and [2-14C]glycine demonstrated that the cyanide carbon originates from the number 2 carbon of glycine for both P. fluorescens and P. aeruginosa. Cyanide production was not observed in raw industrial wastewater or in sterile wastewater inoculated with pure cultures of cyanogenic Pseudomonas strains. Cyanide was produced when wastewater was amended by the addition of components of the defined growth medium.

Nucleophilic Substitution on 4-Methylbenzyl Thiocyanate with Nucleophiles

Abstract The reactions of 4-methylbenzyl thiocyanate (1) with several nucleophiles have been investigated. Compound 1 possesses three electrophilic sites, i.e., benzylic carbon, sulfur and cyano carbon, to receive nucleophilic attack. PhS− and CN− which have HOMO’s of high energy levels appear to attack preferentially the sulfur atom. MeO− was found to attack preferably the cyanide carbon, while amines which have HOMO’s of low energy levels prefer benzylic carbon to attack. The nucleophilic substitution on the sulfur or the cyanide carbon generates CN− or p-xylene-α-thiolate anion, strong nucleophiles, as the primary products, which then initiate the complex secondary reactions. The selective reactivities of three attacking sites for nucleophiles in 1 have been rationalized in terms of MO theory.

Auger spectra of methyl cyanide and related compounds

The gas phase, electron excited Auger spectra of CH3CN, C2H2, N2, and CH4 are presented and analyzed. The C(KVV) spectrum of CH3CN, which contains two carbon atoms with different local environments, is shown to be consistent with independent contributions from an acetylenic-like, sp hybridized carbon (the cyanide carbon) and from a methyl-like, sp3 hybridized carbon (the terminal methyl carbon). The cyanide N(KVV) spectrum is shown to be similar in shape to that of N2 but shifted in energy. Analysis of the CH3CN spectrum on a two-hole binding energy scale shows that the Auger process leads to the same set of doubly ionized final states starting from different core–hole sites in the molecule, but with intensities modulated by the polarization of individual molecular orbitals, i.e., the variation of the electron density local to the various atomic sites represented by a particular molecular orbital. In addition, it is shown that the interaction of the two final-state holes resulting from the Auger transition gives rise to shifts of the spectrum towards lower kinetic energies with respect to that predicted for noninteracting holes, and that these shifts vary in magnitude across the Auger feature.

Reactions of trans- and cis-Dichlorobis(benzonitrile)platinum(II) with Acetylacetonate and Benzoylacetonate Carbanions. Formation of N-Acetyl β-Ketoamine Complexes by the Acetyl Group Migration

Abstract trans-Dichlorobis(benzonitrile) platinum(II) reacted with twice the molar amount of thallium(I) acetylacetonate and benzoylacetonate in dichloromethane at room temperature to afford mainly N-acetyl β-ketoamine chelates, trans-[Pt{N(COMe)=C(Ph)CH=COMe(and Ph)}2] (1a and 3a). This N,O-chelate structure of 1a was determined by X-ray analysis. Reactions of cis-[PtCl2(PhCN)2] gave C-acetyl and C-benzoyl β-ketoamine chelates, cis-[Pt{NH=C(Ph)C(COMe(and Ph))=COMe}2], together with other minor products. Formation of these β-ketoamine chelates is explained by the nucleophilic reactions of the β-diketonate carbanions at the coordinated cyanide carbon atom, followed by migration of the acetyl group or the methine proton of the nucleophiles onto the imino nitrogen atom formed during these reactions. In the presence of free β-diketones, migration of the acyl group was generally suppressed; this led to high yields of C-acyl complexes especially in reactions of cis-[PtCl2(PhCN)2]. In each case, the reaction proceeded with retention of the geometrical configuration around the central metal atom. The structures of other products, including a compound obtained by acid hydrolysis of 1a, were explored and discussed, based on IR and 2H NMR data.

The Isolation, Characterization, and Isomerization of cis- and trans-Bis(benzonitrile)dichloroplatinum(II)

Abstract The reaction of platinum(II) chloride with neat benzonitrile gave bis(benzonitrile)dichloroplatinum(II) as a mixture of cis and trans isomers in variable proportions, depending on the temperature. The geometry of the chromatographically separated isomers was identified on the basis of the dipole-moment and IR data. The 13C NMR spectra in CDCl3 also enabled us to discriminate between isomers in both chemical shift and coupling to the 195Pt of the cyanide carbon, the resonance peak of which was utilized to follow the isomerization. The rate constant (kc) for the cis-to-trans isomerization was found to be (3.8±0.3)×10−6 s−1 in CDCl3 at 25 °C, ten times larger than that [kt=(2.9±0.2)×10−7 s−1] of the reverse reaction. The equilibrium between cis and trans strongly favored trans in CDCl3 at 25 °C, whereas in benzonitrile the cis form was the dominant species at room temperature, while the trans form was dominant at higher temperatures.