CNC Angle Research Articles

Structure and nuclear quadrupole coupling interaction in hydroxylamines: The rotational spectrum of N,N-diethyl(2H)hydroxylamine

The ground-state rotational spectrum of N,N-diethyl(2H)hydroxylamine (C2H5-NOD-C2H5) was measured by Fourier transform microwave spectroscopy. Six rotational transition lines were assigned to the most stable conformer with the alkyl chain in the trans arrangement and the hydroxyl trans to the bisector of the CNC angle, that is, with the NOD frame in the bc-symmetry plane. Rotational constants are A= 7210.938(2), B= 2018.628(1), and C= 1739.696(1) MHz. These data together with those previously determined for the parent species and 13C and 15N isotopologues, were used to determine a partial r0 structure. The hyperfine structure due to the nuclear quadrupole coupling (NQC) interaction of both 14N and D nuclei was disentangled allowing to obtain the diagonal NQC-constants. On the basis of the determined geometry, the NQC-tensor values in the electric field-gradient principal axis system were determined (χxxN= 0.71, χyyN= 5.90, χzzN= −6.61 MHz; χxxD= −0.11, χyyD= −0.15, χzzD= 0.26 MHz). Comparison with other amines shows that using ammonia as reference, χzzN can be estimated with an additive model: +0.4 and +1.7 MHz from hydrogen to alkyl and hydroxyl substitution, respectively. From the analysis of the available data on the 1:1 water complex of N,N-diethylhydroxylamine, a 8% electric field gradient decrease at the nitrogen nucleus due to the formation of the hydrogen bond involving the nitrogen lone pair was found.

Crystal Engineering of Ionic Cocrystals Sustained by Azolium···Azole Heterosynthons.

Crystal engineering of multi-component molecular crystals, cocrystals, is a subject of growing interest, thanks in part to the potential utility of pharmaceutical cocrystals as drug substances with improved properties. Whereas molecular cocrystals (MCCs) are quite well studied from a design perspective, ionic cocrystals (ICCs) remain relatively underexplored despite there being several recently FDA-approved drug products based upon ICCs. Successful cocrystal design strategies typically depend on strong and directional noncovalent interactions between coformers, as exemplified by hydrogen bonds. Understanding of the hierarchy of such interactions is key to successful outcomes in cocrystal design. We herein address the crystal engineering of ICCs comprising azole functional groups, particularly imidazoles and triazoles, which are commonly encountered in biologically active molecules. Specifically, azoles were studied for their propensity to serve as coformers with strong organic (trifluoroacetic acid and p-toluenesulfonic acid) and inorganic (hydrochloric acid, hydrobromic acid and nitric acid) acids to gain insight into the hierarchy of NH+···N (azolium-azole) supramolecular heterosynthons. Accordingly, we combined data mining of the Cambridge Structural Database (CSD) with the structural characterization of 16 new ICCs (11 imidazoles, 4 triazoles, one imidazole-triazole). Analysis of the new ICCs and 66 relevant hits archived in the CSD revealed that supramolecular synthons between identical azole rings (A+B-A) are much more commonly encountered, 71, than supramolecular synthons between different azole rings (A+B-C), 11. The average NH+···N distance found in the new ICCs reported herein is 2.697(3) Å and binding energy calculations suggested that hydrogen bond strengths range from 31-46 kJ mol-1. The azolium-triazole ICC (A+B-C) was obtained via mechanochemistry and differed from the other ICCs studied as there was no NH+···N hydrogen bonding. That the CNC angles in imidazoles and 1,2,4-triazoles are sensitive to protonation, the cationic forms having larger (approximately 4.4 degrees) values than comparable neutral rings, was used as a parameter to distinguish between protonated and neutral azole rings. Our results indicate that ICCs based upon azolium-azole supramolecular heterosynthons are viable targets, which has implications for the development of new azole drug substances with improved properties.

Spectroscopic and quantum mechanical study of a scavenger molecule: N,N-diethylhydroxylamine

We report a combination of quantum mechanical calculations and a range of spectroscopic measurements in the gas phase of N,N-diethylhydroxylamine, an important scavenger compound. Three conformers were observed by pulsed jet Fourier transform microwave spectroscopy in the 6.5–18.5 GHz frequency range. They are characterized by the hydroxyl hydrogen atom being in trans orientation with respect to the bisector of the CNC angle while the side alkyl chains can be both trans (global minimum, Cs symmetry, A = 7608.1078(4), B = 2020.2988(2) and C = 1760.5423(2) MHz) or one trans and the other gauche (second energy minimum, A = 5302.896(1), B = 2395.9822(4) and C = 1804.8567(3) MHz) or gauche’ (third energy minimum, A = 5960.8025(6), B = 2273.6627(4) and C = 1975.8074(4) MHz). For the global minimum, the 13Cα,13Cβ and 15N isotopologues were observed in natural abundance, allowing for an accurate partial structure determination. Moreover, several lines were detected by free jet absorption millimeter wave spectroscopy in the 59.6–74.4 GHz spectral range. The electron binding energies of the highest occupied molecular orbital and the next-to-highest occupied molecular orbital, determined by photoelectron spectroscopy, are 8.95 and 10.76 eV, respectively. Supporting calculations evidence that, (i) upon ionization of the HOMO, the molecular structure changes from an amine to an N-oxoammonium arrangement and (ii) the 0–0 of the HOMO-1 photoionization is 10.46 eV. The K-shell binding energies, determined by X-ray photoelectron spectroscopy, are 290.42 eV (Cβ), 291.45 eV (Cα), 405.98 eV (N) and 538.75 eV (O). The Fourier transform near infrared spectrum is reported and a tentative assignment is proposed. The equilibrium wavenumber (ω̃ = 3811 cm−1) and the anharmonicity constant (ω̃χ = −87.5 cm−1) of the hydroxyl stretching mode were estimated using a quadratic model.

Rotational Spectra and Structures of Phenyl Isocyanate and Phenyl Isothiocyanate.

The pure rotational spectra of phenyl isocyanate (PhNCO) and phenyl isothiocyanate (PhNCS) were investigated using Fourier transform microwave spectroscopy in the range from 4 to 26 GHz. For each molecule, rotational transitions due to the parent species and nine minor isotopologues including seven 13C, one 15N, and one 18O/34S have been observed in natural abundance. The rm(1) geometries were derived from the resulting sets of rotational constants and are consistent with the equilibrium structures (re) from ab initio calculations performed at the MP2/aug-cc-pVTZ level. NBO and Townes-Dailey analyses were conducted to better understand the electronic structure and geometry of each compound. In the case of PhNCS, the nitrogen atom displays more sp-like character resulting in shorter C-N bonds and a larger CNC angle relative to those of PhNCO.

SYNTHESIS AND STRUCTURE OF POTASSIUM TETRAETHYLAMMONIUM HEXATHIOCYANATOPLATINATE(IV)

Potassium tetraethylammonium hexathiocyanatoplatinate(IV) (Et4N)(K)[Pt(SCN)6] (I) was synthesized by the reaction of potassium hexathiocyanatoplatinate(IV) with tetraethylammonium chloride in acetonitrile aqueous solution. Slow evaporation of the solvent led to the formation of large red-brown crystals. The product structure was determined by XRDA. The X-ray diffraction pattern of crystal I was carried out on a Bruker D8 QUEST diffractometer (MoKα radiation, λ = 0.71073 Å, graphite monochromator). [С14H20N7KPtS6, M = 712.92, Crystal system monoclinic, space group C 2/c, a = 10.432(8), b = 14.767(13), c = 16.300(13) Å, V = 2510(4) Å3, Z = 4, µ = 6.272 mm-1, F(000) = 1384, crystal size 0.86×0.66×0.50 mm]. The tetrahedral configuration of the tetraethylammonium cation is slightly distorted (CNC angles are 105.5(5)º-111.8(4)º, bond lengths N-С are 1.503(5)-1.519(5) Å). Platinum ions in anions have octahedral coordination (trans-angles SPtS are 180º, cis-angles SPtS are (88.47(4)º-91.53(4)º). The bond lengths Pt-S are equal to 2.373 (2)-2.37(2) Å. Potassium cations are coordinated by six nitrogen atoms of thiocyanate groups (distances N K (2.828(4)-2.896 (4) Å). Trans-angles NKN (128.44 (15)º-146.9 (2)º) are far from ideal values for the octahedron. Bridged thiocyanate ligands are bonded cations of the platinum and potassium. Ambidentate thiocyanate ligands are simultaneously coordinated to the K+ cation by nitrogen atoms. By means of the bridged thiocyanate ligands a three-dimensional coordination polymer is formed. The resulting structure is a three-dimensional grid, in the cells of which the cations of tetraethylammonium (Et4N)+ are located.

Probing Disorder in Al-ZSM-5 Zeolites by 14N NMR Spectroscopy

14N solid-state NMR spectroscopy is used to investigate and quantify the nanometer scale disorder promoted by Al/Si substitution in ZSM-5 zeolites. After a preliminary characterization by SEM, XRD, and multinuclear (1H, 13C, 19F, 27Al, 29Si) solid-state NMR, the 14N MAS NMR spectra of a series of as-synthesized ZSM-5 zeolites containing various amounts of Al are analyzed. The 14N spinning sideband patterns are shown to evolve with the Si/Al ratio. The modeling of the NMR spectra allows one to estimate the local disorder arising from the Al site distribution within the tetrahedral sites of the zeolites, the variations of F locations, and the presence of silanol defects. The influence of the zeolite framework modifications due to Al/Si substitution on 14N NMR parameters is discussed on the basis of the results obtained with the Density Functional Theory periodic quantum chemical calculations augmented with an empirical London dispersion term. Analysis of the results highlighted the influence of CNC angle va...

Conformational, NBO, NLO, HOMO-LUMO, NMR, electronic spectral study and molecular docking study of N,N-Dimethyl-3-(10H-phenothiazin-10-yl)-1-propanamine

FT-IR and FT-Raman spectra of N,N-Dimethyl-3-(10H-phenothiazin-10-yl)-1-propanamine were recorded and analyzed. The conformational behaviour is also investigated. The vibrational wave numbers were calculated using density functional quantum chemical calculations. The data obtained from wave number calculations are used to assign vibrational bands obtained experimentally. In the most stable form for N,N-Dimethyl-3-(10H-phenothiazin-10-yl)-1-propanamine, the nitrogen atom of the phenothiazine ring is predicted to adopt an expanded pyramidal configuration with an average CNC angle of 118° while the alkylamine chain points away from the phenothiazine ring. The geometrical parameters are compared with related structures. The stability of the molecule arising from hyper conjugative interaction and charge delocalization has been analyzed using natural bonding orbital analysis. The frontier molecular orbital analysis is used to determine the charge transfer within the molecule. The theoretical NMR spectral analysis, Fukui functions and electronic transition UV–Vis spectral analysis is also reported. The docked title compound forms a stable complex with Plasmodium falciparum and gives a binding affinity value of −6.8 kcal/mol and the results suggest that the compound might exhibit inhibitory activity against Plasmodium falciparum.

Synthesis and Microwave Spectrum of Vinyl Isoselenocyanate (H2C═CHNCSe), a Compound with a Quasilinear CNCSe Chain

The first α,β-unsaturated isoselenocyanate, vinyl isoselenocyanate (H(2)C═CHNCSe), has been synthesized, and its microwave spectrum has been investigated in the 11.5-77.0 GHz spectral range. The microwave work was augmented by quantum chemical calculations using four different methods, namely, CCSD(T), CCSD, B3LYP, and M062X, with the cc-pVTZ basis set. It is generally assumed that two rotamers having the isoselenocyanide group in an antiperiplanar or a synperiplanar position can exist for this compound. However, these four methods all predict that there is only one rotameric form of the molecule, namely, the antiperiplanar form. The CNC angle of the antiperiplanar rotamer is calculated to vary from 151° to 170° depending on the quantum chemical methodology. CCSD(T) and B3LYP potential functions of the in-plane CNC bending vibrations were calculated. These functions have one shallow minimum corresponding to the antiperiplanar form. The spectra of the ground and one vibrationally excited state of this rotamer were assigned. Spectral searches for the synperiplanar form were performed but were not successful, so this form must have a relatively high energy, if it exists at all. The vibrationally excited state is presumably the lowest in-plane bending vibration of the CNC angle. Relative intensity measurements yielded a very low frequency of 18(25) cm(-1) for this vibration. The large-amplitude vibration of this mode suggests that this compound should rather be regarded as having a quasilinear CNCSe link of atoms than a rigid, bent antiperiplanar form.

Synthesis and structure of bismuth complex [n-Bu4N] 2 + [Bi2I8 · 2 Me2S=O]2−

Bismuth complex [Bu4N]2+[Bi2I8 · 2Me2S=O]2−(I) was synthesized by reacting tetrabutylammonium iodide with bismuth iodide. In the cations, an N atom has a distorted tetrahedral coordination (CNC angles change in the range from 107.9(5)° to 111.9(5)°). In the centrosymmetric binuclear anion, octahedral bismuth atoms are bound to each other through the bridging (br) iodine atoms (Bi-Ibr, 3.2779(7) A and 3.3156(9) A), which are coplanar with four terminal (t) iodine atoms (Bi-It, 2.9392(7) A and 2.9534(8) A). Two remaining positions near the bismuth atom are occupied by an iodine atom (Bi-I, 3.0079(8) dimethyl sulfoxide (DMSO) molecule (Bi-O, 2.456(5) A).

Reactions of bismuth iodide with ammonium, phosphonium, and bismuthonium salts

The reactions of ammonium, phosphonium, and bismuthonium salts with bismuth iodide were used to synthesize a series of complex compounds with bismuth-containing anions: [(HOC2H4)3NH]+ 4[Bi4I16]4−, [Ph3EtP] 3 + [Bi2I9]3−, and [Ph4Bi] 3 + [Bi5I18]3−. X-ray diffraction data show that the nitrogen atoms in the two types of crystallographically independent cations of the nitrogen-containing complex possess a distorted tetrahedral coordination [the CNC angles are 110.3(9)°–113.2(9)°]. In the tetranuclear centrosymmetric [Bi4I16]4− anion, the bismuth atoms have an octahedral coordination: Two types of groups, BiI2 and BiI3, are bound with one another by four μ2-and two μ3-iodine bridges (the Bi-I-μ2, Bi-I-μ3, and Bi-I-μ1 distances are 3.1296(10), 3.2808(8); 3.3210(8) and 2.8670(8)–2.9108(9) A, respectively). The coordination of the phosphorus atom in the [Ph3EtP]+ cations of the phosphorus-containing complex is close to tetrahedral (the CPC angles are 107.5°–114.1°). In the binuclear [Bi2I9]3− anions, the bismuth atoms have an octahedral coordination. The axial I-Bi-I angles are 167.52(2)°, 169.84(2)°, and 174.97(2)°. The terminal BiI3 fragments [Bi2-I7,8,9 2.9238(7), 2.9236(7), and 2.9522(7) A] are in the eclipsed conformation.

Extremely narrow SiON angles in siloxy-substituted nitrogen-containing rings: a computational investigation

Quantum chemical calculations have been performed for a number of siloxy derivatives of pyrrolidine and piperidine in an attempt to gauge the effect of the saturated ring on the SiON angle. Most derivatives of pyrrolidine had SiON angles comparable to those previously observed for substituted N,N-dimethylhydroxylamines. However, piperidine derivatives were predicted to have particularly narrow SiON angles. Anti, anti, axial-F(3)SiO-piperidine was found to have an angle of 82.9 degrees , smaller than the narrowest angle observed by experiment in the gas phase, for (F(3)C)F(2)SiONMe(2). The size of the ring and, in particular, the CNC angle appears to play a crucial role in determining the SiON angle. Further calculations including other heterocyclic rings were therefore performed to help explain this finding. Using the (F(3)C)F(2)SiO- group as a substituent on nitrogen allowed SiON angles of less than 80 degrees to be calculated for several five-, six- and seven-membered rings.

Molecular Structure and Reactivity of Tri(1-cyclohepta-2,4,6-trienyl)amine, N(C7H7)3

Abstract Compared with the tertiary phosphane P(C7H7)3 (1), the amine N(C7H7)3 (2) possesses the structure of a flattened trigonal pyramid with a sum of CNC angles of 350.0° (cf. 300.2° (av.) in 1). The heteroatom (with the lone pair) is situated 27.0 pm above the C3 basal plane in 2, but 86.4 pm in 1. The amines N(C7H7)3 (2), NH(C7H7)2 (2a) and N(Ph)(C7H7)2 (2b) react with tropylium tetrafluoroborate, [C7H7]BF4, to give N-tropylidene-(1-cyclohepta-2,4,6-trienyl)-immonium tetrafluoroborates, [(C7H6)N(R)(C7H7)]BF4 3 (R = H, from 2 and 2a), 4 (R = Ph, from 2b), which have been characterized by their IR and NMR (1H, 13C) spectra.

An evaluation of amide group planarity in 7-azabicyclo[2.2.1]heptane amides. Low amide bond rotation barrier in solution.

Here we show that amides of bicyclic 7-azabicyclo[2.2.1]heptane are intrinsically nitrogen-pyramidal. Single-crystal X-ray diffraction structures of some relevant bicyclic amides, including the prototype N-benzoyl-7-azabicyclo[2.2.1]heptane, exhibited nitrogen-pyramidalization in the solid state. We evaluated the rotational barriers about the amide bonds of various N-benzoyl-7-azabicyclo[2.2.1]heptanes in solution. The observed reduction of the rotational barriers of the bicyclic amides, as compared with those of the monocyclic pyrrolidine amides, is consistent with a nitrogen-pyramidal structure of 7-azabicyclo[2.2.1]heptane amides in solution. A good correlation was found between the magnitudes of the rotational barrier of N-benzoyl-7-azabicyclo[2.2.1]heptanes bearing para-substituents on the benzoyl group and the Hammett's sigma(p)(+) constants, and this is consistent with the similarity of the solution structures. Calculations with the density functional theory reproduced the nitrogen-pyramidal structures of these bicyclic amides as energy minima. The calculated magnitudes of electron delocalization from the nitrogen nonbonding n(N) orbital to the carbonyl pi orbital of the amide group evaluated by application of the bond model theory correlated well with the rotational barriers of a variety of amides, including amides of 7-azabicyclo[2.2.1]heptane. The nonplanarity of the amide nitrogen of 7-azabicyclo[2.2.1]heptanes would be derived from nitrogen-pyramidalization due to the CNC angle strain and twisting of the amide bond due to the allylic strain.

The structures of the azido-, isocyanato- and isothiocyanato- derivatives of methane and silane and their derivatives. A comparison of ab initio with experimental results

The equilibrium structures of various conformers of the azides, isocyanates and isothiocyanates with general type Me 3− n H n W–NXY, together with a small number of their halogenated derivatives, have been determined by Möller–Plessett (MP2) calculations under standard triple zeta valence + polarisation basis set conditions. The structures are compared with each other, with previous and other theoretical studies including CCSD(T) results, and with experimental spectral and diffraction results. The MP2 and CCSD(T) results correlate strongly for a series of these molecules; thus the CCSD(T) bond lengths are larger by about 1.9%. The angles are little different, partly as a result of balancing effects; where some CNN and CNC angles are smaller in CCSD(T) by ∼2–3°, but some CCSD(T) dihedral angles HCNN and HCNC are larger. The MP2 results for the wider group correlate closely with microwave and infrared spectra, and with electron diffraction data. In contrast, the B3LYP method, with the same bases, whilst apparently giving reasonable structures, gives very poor rotation constants, as a result of poor CNC angle determination. The present results suggest that the spectra of ethyl isocyanate, silyl azide, trimethylsilyl azide, and silyl isocyanate require reinvestigation. This is part of a wider study where the central atom W is the series of Group 14 tetrahedral atoms up to Pb; in this study, the central atom W is C and Si, with XY either NN, CO or CS.

L'échelle pKHBde basicité de liaison hydrogène des amines tertiaires aliphatiques

The hydrogen bond acceptor strength of 40 tertiary amines has been measured by Fourier transform – infrared (FTIR) spectrometry from their 1:1 complexation constant towards 4-fluorophenol in CCl4at 25°C (the pKHBscale). Also measured was the frequency shift, Δν(OH), of the ν(OH) band of methanol hydrogen-bonded to these amines. The comparison of the thermodynamic hydrogen bond basicity scale, pKHB, with the spectroscopic one, Δν(OH), and with the Brønsted pKascale, points to the great sensitivity of pKHBto steric effects. The pKHBscale of tertiary amines extends from 2.71 for quinuclidine to –0.34 for N,N-diisopropyl-3-pentylamine. The main factors governing this important variation (17 kJ·mol–1on the Gibbs energy scale) are the electron-withdrawing inductive effect and various kinds of steric effects (e.g., opening of the CNC angles and hindrance to OH fixation on the nitrogen lone pair). Infrared (IR) spectra show the attachment of 4-fluorophenol to the nitrile nitrogen of Me2NCH2C[Formula: see text]N and Me2NCH2CH2C[Formula: see text]N, to the oxygen of N-methylmorpholine, and to the π electrons of (HC[Formula: see text]CCH2)3N and (PhCH2)3N, in addition to the attachment to the amino nitrogen. In (PhCH2)3N, the electron-withdrawing effect of the three benzyl substituents and, mainly, the very important congestion of the nitrogen lone pair reduce the nitrogen hydrogen-bond basicity almost to nothing, so that tribenzylamine, a nitrogen Brønsted base, turns to a π base in hydrogen bonding. From this example, the large differences between the pKHBand pKascales of organic bases are emphasized.Key words: basicity, hydrogen bonding, tertiary amines, pKHBscale.

Structural features of aliphatic N-nitrosamines of 7-azabicyclo[2.2.1]heptanes that facilitate N-NO bond cleavage.

N-Nitrosamines can be considered as potential nitric oxide (NO)/nitrosonium ion (NO(+)) donors. However, the relation of the structures of N-nitrosamines, in particular of aliphatic N-nitrosamines, to the characteristics of release of NO or NO(+) remains unclear. Here we show that aliphatic N-nitrosoamines of 7-azabicyclo[2.2.1]heptanes can undergo heterolytic N-NO bond cleavage. On the basis of the observation of reduced rotational barriers of the N-NO bonds in solution and nitrogen-pyramidal structures of the N-nitroso group in the solid state, we postulate that N-NO bond cleavage of N-nitrosamines is enhanced by a reduction of the resonance in the N-NO group. Computational studies suggest that these structural features of the N-nitrosamines of 7-azabicyclo[2.2.1]heptane are derived from angle strain imposed on the CNC angles.

A MP2 four-dimensional potential energy surface of dimethyl-amine

In this article, the four-dimensional potential energy surface for the double methyl torsion, CNC angle and amine hydrogen wagging in dimethyl-amine was determined using fully optimized MP2/6-31G(d,p) calculations. These four coordinates correspond to the largest amplitude vibrations and confer the non-rigidity properties of the molecule.Calculations of 825 nuclear conformations selected by symmetry considerations and energy criteria, were performed. They have been fitted to an equation which is a sum of a gaussian function and a product of a double Fourier series multiplied by a double Taylor series. The total number of the coefficients are 87. They are the exponent of the gaussian function and 86 linear coefficients. The most significant parameters of this potential are also analyzed. They are the inversion barrier, the torsional barrier and the gearing interaction term between the methyl groups and they are defined as hypersurfaces depending on two or three coordinates. The shape of these surfaces has an important effect on the frequencies.

On the geometry of 3-amino-sydnones

The X-ray structure of molsidomine (3-morpholine-sydnoneimine) reveals a widening of the CNC angle of morpholine substituted at the N3 atom of the sydnone moiety. This might be due to lone-pair delocalization, since sydnone is a mesoionic aromatic heterocycle, and its N3 nitrogen atom is expected to undergo an important π-electron loss. With a view to clarifying this problem, the results of an extensive analysis of the literature and theoretical computations carried out with standard empirical and ab initio methods have been discussed with the help of the IML-EH method, a version of the EHT method which includes hybridization, α localization and mutual charge adjustment. Although the computational results can be interpreted as favouring the prediction that N3 of sydnones is π-electron deficient, no significant delocalization of the lone pair of the amine substituent is predicted. The CNC angle widening appears to be due to hybridization–polarization effects. In the course of the paper, numerical information relevant to further research on the sydnones and on the N–N bond is presented and discussed.

Bis(1,2-bis(diphenylphosphino)ethane)tungsten(0) Complexes Containing Electron-Saturated Metal Centers and Singly-Coordinated Bridging Ligands

Reaction of 1,4-diisocyanobenzene or 4-isocyanobenzonitrile with trans-W(N(2))(2)(DPPE)(2) (DPPE = 1,2-bis(diphenylphosphino)ethane) produced cis-WL(2)(DPPE)(2), where L = 1,4-diisocyanobenzene or 4-isocyanobenzonitrile. cis-(CNC(6)H(4)NC)(2)W(DPPE)(2) crystallizes in the triclinic space group P&onemacr;, with a = 12.848(3) Å, b = 13.596(3) Å, c = 19.072(3) Å, alpha = 78.99(2) degrees, beta = 70.66(2) degrees, gamma = 65.26(2) degrees, V = 2849.8(11) Å(3), and Z = 2. cis-(NCC(6)H(4)NC)(2)W(DPPE)(2) crystallizes in the triclinic space group P&onemacr;, with a = 12.712(3) Å, b = 13.700(3) Å, c = 19.109(3) Å, alpha = 77.91(2) degrees, beta = 70.63(2) degrees, gamma = 64.76(2) degrees, V = 2830.7(13) Å(3), and Z = 2. Both compounds possess a distorted octahedral geometry about the metal center, with the two isocyanide ligands cis to one another. The isocyanide ligands are substantially bent along the CNC axis of the isocyanide group coordinated to tungsten. For the complex containing the symmetric ligand, CNC(6)H(4)NC, the mean CNC angle for the coordinated end of the isocyanide is 139.1(11) degrees, the average W-C bond length is 1.86(1) Å, and the C&tbd1;N bond lengths have a mean value of 1.30(2) Å. These data indicate substantial back-donation from an electron-saturated tungsten atom. This is supported spectroscopically, with substantial shifts to lower wavenumbers for the C-N stretching frequencies of the coordinated isocyanide groups. Similar trends are observed in cis-(NCC(6)H(4)NC)(2)W(DPPE)(2). Both compounds contain electron-rich metals surrounded by large ligands which apparently protect the metals from atmospheric oxidation. The isocyanide ligands in both complexes contain a second coordinating group pointing away from the metal into the environment surrounding the molecules, providing the potential for polymetallic complexes containing metals in a variety of oxidation states.

Comparison of the properties of the 1,1,2,4,5,5-hexacyano-3-aza-penta-1,4-dienide[(NC) 2CC(CN)NC(CN)C(CN) 2] unit as anion and as ligand. Crystal structures of (Et 4N)(C 10N 7) and [{Ag(C 10N 7)} ∞

The previously reported compounds, Et 4N(C 10N 7), 1, and [{Ag(C 10N 7)} ∞], 2, have been structurally characterized by X-ray diffraction. The C 10N 7 unit acts in 1 as a monoanion and in 2 as a sophisticated bridging ligand (via the nitrogen atoms of its four external cyanogroups) leading to a structure with two crystallographically distinct silver cations. The first one has an usual pseudo-tetrahedral coordination, the second one presents an unexpected square planar coordination which is discussed. The geometry of the organic fragment is only slightly modified upon coordination: in both cases, the C 10N 7 unit is essentially planar with central CN bond lengths of 1.317(4) and 1.334(4) Å in 1, 1.33(1) and 1.34(1) Å in 2 and CNC angles of 128.3(3) in 1 and 129.2(9)° in 2. In benzonitrile solutions, the C 10N 7 anion shows two one electron diffusion-controlled reversible reduction rocesses, the first one leading to the radical species [(C 10N 7)] 2− characterized by ESR.