Reactions of Laser-Ablated Fe, Co, and Ni with NO: Infrared Spectra and Density Functional Calculations of MNO+ and M(NO)x (M = Fe, Co, x = 1−3; M = Ni, x = 1, 2), and M(NO)x- (M = Co, Ni; x = 1, 2)

Reaction of nitric oxide molecules on transition-metal-doped silver cluster cations: size- and dopant-dependent reaction pathways

We report size- and dopant-dependent reaction pathways as well as reactivity of gas-phase free Ag_nM⁺ (M = Sc-Ni) clusters interacting with NO. The reactivity of Ag_nM⁺, except for M = Cr and Mn, exhibits a minimum at a specific size, where the cluster cation possesses 18 or 20 valence electrons consisting of Ag 5s and dopant's 3d and 4s. The product ions range from NO adducts, Ag_nM(NO)_m⁺, and oxygen adducts, Ag_nMO_m⁺, to NO₂ adducts, Ag_nM(NO₂)_m⁺. At small sizes, Ag_nMO_m⁺ are the major products for M = Sc-V, whereas Ag_nM(NO)_m⁺ dominate the products for M = Cr-Ni in striking contrast. In both cases, these reaction products are reminiscent of those from an atomic transition metal. However, the reaction pathways are different at least for M = Sc and Ti; kinetics measurements reveal that the present oxygen adducts are formed via NO adducts, while, for example, Ti⁺ is known to produce TiO⁺ directly by reaction with a single NO molecule. At larger sizes, on the other hand, Ag_nM(NO₂)_m⁺ are dominantly produced regardless of the dopant element because the dopant atom is encapsulated by the Ag host; the NO₂ formation on the cluster is similar to that reported for undoped Ag_n⁺.

First multi-tool exploration of a gas-condensate-pyrolysate system from the environment of burning coal mine heaps: An in situ FTIR and laboratory GC and PXRD study based on Upper Silesian materials

A methodological approach to the complex geochemical analysis of the coal fire in burning coal mine heaps (BCMH) of Upper Silesian Coal Basin has been developed. The other approach used is gas chromatography and indicatory tubes. Powder X-Ray Diffraction is applied for phase analysis to determine the species composition of mineral condensates present within and around gas flues. The gas compositions are proved to be extremely variable, when comparing both different BCMH and flues or flue zones of the same heaps. One outstanding determination concerns GeCl₄, found in most samples often in large quantities. No evident dependence between the gas and mineral condensate compositions is found: N-rich condensates may but do not have to be associated with NH₃-, pyridine-, or NO_x-rich gases. This is also true for S-rich and Cl-rich mineralization in connection with gases of SO₂, H₂S, OCS, CS₂, thiophene, dimethyl sulfide, dimethyl disulfide, HCl, and various halogenated hydrocarbons. Fluorine is rarely present as HF, whereas SiF₄ occurs more frequently and in much larger quantities. AsH₃ is mainly a trace gas but may locally be enriched. Besides the common gases, a number of trace gases is also determined based on residual FTIR spectra. Those with the highest presence chance include cyanogen isocyanate, cyanogen N-oxide, (iso)cyanic acid, c-cyanomethanimine (ethylenediimine), isocyanatomethane, iodocyanoacetylene, acetonitrile, acetaldehyde, m-hydroxybenzonitrile (m-cyanophenol), isonitrosyl chloride, nitrosyl isocyanide, difluorosilane, pentacene, triphenylene, thiazolidine, cyclohexane, and a trinitrenetriazine. The occurrence of some metals and semimetals (e.g., Al, Mg, Ga) as neutral hydroxides, suggested by other authors to occur in natural gases, is possibly confirmed. The presence of trace metal carbonyls, nitrosyls and hydrides is also possible.

Nitric oxide functionalized molybdenum(0) pyrazolone Schiff base complexes: thermal and biochemical study

This work describes the synthesis and characterization of three molybdenum dinitrosyl Schiff base complexes of the general formula [Mo(NO)₂(L)(OH)], where L is N-(dehydroacetic acid)-4-aminoantipyrene (dha-aapH), N-(4-acetylidene-3-methyl-1-phenyl-2-pyrazolin-5-one)-4-aminoantipyrine (amphp-aapH) or N-(3-methyl-1-phenyl-4-propionylidene-2-pyrazolin-5-one)-4-aminoantipyrine (mphpp-aapH). The complexes were formulated on the basis of spectroscopic analyses, elemental composition, magnetic susceptibility measurements, molar conductance behaviour and determination of the respective decomposition temperatures. A comparative experimental-theoretical approach was followed to elucidate the structure of the complexes. Fourier transform infra-red (FT-IR) spectroscopy, thermo-gravimetry (TG) and electronic spectral insights were mainly focused on the confirmation of the formation of the complexes. The computational density functional theory (DFT) calculations evaluated in the study involve the molecular specification for the use of LANL2DZ/RB3LYP formalism for metal atoms and 6-311G/RB3LYP for the remaining non-metal atoms. The study reveals a suitable cis-octahedral geometry for the complexes. The TG curve of one of the representative complexes was evaluated to find the respective thermodynamic and kinetic parameters using various physical methods. The Freeman & Carroll (FC) differential method, the Horowitz and Metzger (HM) approximation method, the Coats–Redfern method and the Broido method were employed to present a comparative thermal analysis of the complex. The Broido method proved the best fit to the results for the compound under question. In addition to structural and thermal analyses, the study also deals with the in vitro antimicrobial and anticancer sensitivity of the complexes. The results revealed potent biological properties of the representative complex containing dha-aapH. Cell toxicity tests against COLO-205 human cancer cell line using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay showed an IC₅₀ value of 53.13 μgm mL⁻¹ for the Schiff base and 10.51 μgm L⁻¹ for the respective complex. Similarly the same complex proved to be an effective antimicrobial agent against Aspergillus, Pseudomonas, E. coli and Streptococcus. The results indicated a more pronounced activity against Pseudomonas and Streptococcus than the other two microbial species.

This work describes the thermal and biological implications of three pyrazolone-dinitrosylmolybdenum(0) complexes.

Density functionalized [RuII(NO)(Salen)(Cl)] complex: Computational photodynamics and in vitro anticancer facets

Photodynamic therapy (PDT) is a treatment that uses photosensitizing agents to kill cancer cells. Scientific community has been eager for decades to design an efficient PDT drug. Under such purview, the current report deals with the computational photodynamic behavior of ruthenium(II) nitrosyl complex containing N, N'-salicyldehyde-ethylenediimine (SalenH₂), the synthesis and X-ray crystallography of which is already known [Ref. 38,39]. Gaussian 09W software package was employed to carry out the density functional (DFT) studies. DFT calculations with Becke-3-Lee-Yang-Parr (B3LYP)/Los Alamos National Laboratory 2 Double Z (LanL2DZ) specified for Ru atom and B3LYP/6-31G(d,p) combination for all other atoms were used using effective core potential method. Both, the ground and excited states of the complex were evolved. Some known photosensitizers were compared with the target complex. Pthalocyanine and porphyrin derivatives were the compounds selected for the respective comparative study. It is suggested that effective photoactivity was found due to the presence of ruthenium core in the model complex. In addition to the evaluation of theoretical aspects in vitro anticancer aspects against COLO-205 human cancer cells have also been carried out with regard to the complex. More emphasis was laid to extrapolate DFT to depict the chemical power of the target compound to release nitric oxide. A promising visible light triggered nitric oxide releasing power of the compound has been inferred. In vitro antiproliferative studies of [RuCl₃(PPh₃)₃] and [Ru(NO)(Salen)(Cl)] have revealed the model complex as an excellent anticancer agent. From IC₅₀ values of 40.031mg/mL in former and of 9.74mg/mL in latter, it is established that latter bears more anticancer potentiality. From overall study the DFT based structural elucidation and the efficiency of NO, Ru and Salen co-ligands has shown promising drug delivery property and a good candidacy for both chemotherapy as well as light therapy.

Photochemically induced intramolecular six-electron reductive elimination and oxidative addition of nitric oxide by the nitridoosmate(VIII) anion

UV photolysis of the nitridoosmate(VIII) anion, OsO3 N(-) , in low-temperature frozen matrices results in nitrogen-oxygen bond formation to give the Os(II) nitrosyl complex OsO2 (NO)(-) . Photolysis of the Os(II) nitrosyl product with visible wavelengths results in reversion to the parent Os(VIII) complex. Formally a six-electron reductive elimination and oxidative addition, respectively, this represents the first reported example of such an intramolecular transformation. DFT modelling of this reaction proceeds through a step-wise mechanism taking place through a side-on nitroxyl Os(VI) intermediate, OsO2 (η(2) -NO)(-) .

Infrared photodissociation spectroscopy of iron nitrosyl cation complexes: Fe(NO)n⁺ (n = 1-5)

Infrared spectra of mass-selected mononuclear iron nitrosyl cations Fe(NO)n(+) with n = 1-5 and their argon tagged complexes are measured via infrared photodissociation spectroscopy in the nitrosyl stretching frequency region in the gas phase. The structures are established by comparison of the experimental spectra with the simulated spectra derived from density functional calculations. Two IR active bands were observed for the argon-tagged Fe(NO)2(+) and Fe(NO)3(+) complexes, consistent with theoretical predictions that these complexes have bent C(2v) and nonplanar C(3v) symmetry, respectively. The Fe(NO)4(+) complex was characterized to have a completed coordination sphere with 17 electrons containing a bent one-electron NO ligand and three three-electron NO ligands. The Fe(NO)5(+) complex was determined to involve a Fe(NO)4(+) core ion that is solvated by an external NO molecule.

Electronic propensity of Cu(II) versus Cu(I) sites in zeolites to activate NO — Spin- and orbital-resolved Cu–NO electron transfer

Electronic factors responsible for the notable decline of NO activation by Cu(II) with respect to Cu(I) sites in zeolites are investigated within spin-resolved analysis of electron transfer channels between the copper center and the substrate. The results of natural orbitals for chemical valence (NOCV) charge transfer analysis for a minimal model of Cu(II) sites in zeolite ZSM-5 ({T1Cu}+ NO) are compared with those for Cu(I)–NO and referenced to an interaction of NO with bare Cu+ cations. The bonding of NO, which is an open-shell and non-innocent ligand, gives rise to a noticeable nondynamical correlation in the adduct with Cu(II) (reflected in a broken-symmetry solution obtained at the density functional theory (DFT) level). Four distinct components of electron transfer between the copper and NO are identified: (i) donation of an unpaired electron from the NO π∥* antibonding orbital to the Cu species, (ii) backdonation from copper d⊥ to the NO antibonding orbital, (iii) “covalent” donation from NO π∥ and Cu d∥ orbitals to the bonding region, and (iv) donation from the nitrogen lone pair to Cus,d. Large variations in channel identity and significance may be noted among studied systems and between spin manifolds: channel i is effective only in the bonding of NO with either a naked Cu+ cation or Cu(II) site. Channel ii comes into prominence only for the model of the Cu(I) site: it strongly activates the NO bond by populating antibonding π*, which weakens the N–O bond, in contrast to channel i depopulating the antibonding orbital and strengthening the N–O bond. Channels iii and iv, however, may contribute to the strength of the bonding between NO and copper, and are of minor importance for the activation of the NO bond. This picture perfectly matches the IR experiment: interaction with either Cu(II) sites or a naked Cu+ cation imposes a comparable blue-shift of NO stretching frequency, while the frequency becomes strongly red-shifted for a Cu(I) site in ZSM-5 due to enhanced π* backdonation.

THEORETICAL STUDY OF NITROGEN MONOXIDE ADSORPTION ON RHODIUM CLUSTERS AT DIFFERENT SITES

The adsorption of nitrogen monoxide NO with charged and neutral [Formula: see text] clusters at atop, bridge, and threefold hollow sites had been investigated by density functional theory calculations. The results showed that rhodium clusters had strong orbital interactions with NO and formed the complex [ Rh n NO ]-/0/+. The stretching vibrational frequencies of the N–O bonds changed with the different adsorption sites and clusters sizes. The interactions between rhodium clusters and NO molecular could be described through the donation and back-donation of their frontier orbitals. The more back donation from Rh to NO , the weaker the N–O bonds, exhibiting that the lengthening of the N–O bond length and the lowering of its vibrational frequency. In general, the donation and back-donation interactions followed the tendencies: anionic > neutral > cationic, big size > small size, threefold hollow site > bridge site > atop site.

A structure-based analysis of the vibrational spectra of nitrosyl ligands in transition-metal coordination complexes and clusters

The vibrational spectra of nitrogen monoxide or nitric oxide (NO) bonded to one or to several transition-metal (M) atom(s) in coordination and cluster compounds are analyzed in relation to the various types of such structures identified by diffraction methods. These structures are classified in: (a) terminal (linear and bent) nitrosyls, [M(σ-NO)] or [M(NO)]; (b) twofold nitrosyl bridges, [M2(μ2-NO)]; (c) threefold nitrosyl bridges, [M3(μ3-NO)]; (d) σ/π-dihaptonitrosyls or "side-on" nitrosyls; and (e) isonitrosyls (oxygen-bonded nitrosyls). Typical ranges for the values of internuclear N-O and M-N bond-distances and M-N-O bond-angles for linear nitrosyls are: 1.14-1.20 Å/1.60-1.90 Å/180-160° and for bent nitrosyls are 1.16-1.22 Å/1.80-2.00 Å/140-110°. The [M2(μ2-NO)] bridges have been divided into those that contain one or several metal-metal bonds and those without a formal metal/metal bond (M⋯M). Typical ranges for the M-M, N-O, M-N bond distances and M-N-M bond angles for the normal twofold NO bridges are: 2.30-3.00 Å/1.18-1.22 Å/1.80-2.00 Å/90-70°, whereas for the analogous ranges of the long twofold NO bridges these are 3.10-3.40 Å/1.20-1.24 Å/1.90-2.10 Å/130-110°. In both situations the N-O vector is approximately at right angle to the M-M (or M⋯M) vector within the experimental error; i.e. the NO group is symmetrical bonded to the two metal atoms. In contrast the threefold NO bridges can be symmetrically or unsymmetrically bonded to an M3-plane of a cluster compound. Characteristic values for the N-O and M-N bond-distances of these NO bridges are: 1.24-1.28 Å/1.80-1.90 Å, respectively. As few dihaptonitrosyl and isonitrosyl complexes are known, the structural features of these are discussed on an individual basis. The very extensive vibrational spectroscopy literature considered gives emphasis to the data from linearly bonded NO ligands in stable closed-shell metal complexes; i.e. those which are consistent with the "effective atomic number (EAN)" or "18-electron" rule. In the paucity of enough vibrational spectroscopic data from complexes with only nitrosyl ligands, it turned out to be very advantageous to use wavenumbers from the spectra of uncharged and saturated nitrosyl/carbonyl metal complexes as references, because the presence of a carbonyl ligand was found to be neutral in its effect on the ν(NO)-values. The wide wavenumber range found for the ν(NO) values of linear MNO complexes are then presented in terms of the estimated effects of net ionic charges, or of electron-withdrawing or electron-donating ligands bonded to the same metal atom. Using this approach we have found that: (a) the effect for a unit positive charge is [plus 100 cm(-1)] whereas for a unit negative charge it is [minus 145 cm(-1)]. (b) For electron-withdrawing co-ligands the estimated effects are: terminal CN [plus 50 cm(-1)]; terminal halogens [plus 30 cm(-1)]; bridging or quasi-bridging halogens [plus 15 cm(-1)]. (c) For electro donating co-ligands they are: PF3 [plus 10 cm(-1)]; P(OPh)3 [-30 cm(-1)]; P(OR)3 (R=alkyl group) [-40 cm(-1)]; PPh3 [-55 cm(-1)]; PR3 (R=alkyl group) [-70 cm(-1)]; and η5-C5H5 [-60 cm(-1)]; η5-C5H4Me [-70 cm(-1)]; η5-C5Me5 [-80 cm(-1)]. These values were mostly derived from the spectra of nitrosyl complexes that have been corrected for the presence of only a single electronically-active co-ligand. After making allowance for ionic charges or strongly-perturbing ligands on the same metal atom, the adjusted 'neutral-co-ligand' ν(NO)*-values (in cm(-1)) are for linear nitrosyl complexes with transition metals of Period 4 of the Periodic Table, i.e. those with atomic orbitals (…4s3d4p): [ca. 1750, Cr(NO)]; [1775,Mn(NO)]; [1796,Fe(NO)]; [1817,Co(NO)]; [ca. 1840, Ni(NO)]. Period 5 (…5s4d5p): [1730 Mo(NO)]; [-, Tc(NO)]; [1745,Ru(NO)]; [1790,Rh(NO)]; [ca. 1845, Pd(NO)]. Period 6 (…6s4f5d6p), [1720,W(NO)]; [1730,Re(NO)]; [1738,Os(NO)]; [1760,Ir(NO)]; [-, Pt] respectively. Environmental differences to these values, e.g. data taken in polar solutions or in the crystalline state, can cause ν(NO)* variations (mostly reductions) of up to ca. 30 cm(-1). Three spectroscopic criteria are used to distinguish between linear and bent NO groups. These are: (i) the values of ν(14NO) themselves, and (ii) the isotopic band shift--(IBS)--parameter which is defined as [ν(14NO)-ν(15NO)], and, (iii) the isotopic band ratio--(IBR)--given by [ν(15NO/ν14NO)]. The former is illustrated with the ν(14NO)-data from trigonal bipyramidal (TBP) and tetragonal pyramidal (TP) structures of [M(NO(L)4] complexes (where M=Fe, Co, Ru, Rh, Os, Ir and L=ligand). These values indicate that linear (180-170°) and strongly bent (130-120°) NO groups in these compounds absorb over the 1862-1690 cm(-1) and 1720-1525 cm(-1)-regions, respectively. As was explicitly demonstrated for the linear nitrosyls, these extensive regions reflect the presence in different complexes of a very wide range of co-ligands or ionic charges associated with the metal atom of the nitrosyl group. A plot of the IBS parameter against M-N-O bond-angle for compounds with general formulae [M(NO)(L)y] (y=4, 5, 6) reveals that the IBS-values are clustered between 45 and 30 cm(-1) or between 37 and 25 cm(-1) for linear or bent NO groups, respectively. A plot of IBR shows a less well defined pattern. Overall it is suggested that bent nitrosyls absorb ca. 60-100 cm(-1) below, and have smaller co-ligand band-shifts, than their linear counterparts. Spectroscopic ν(NO) data of the bridging or other types of NO ligands are comparatively few and therefore it has not been possible to give other than general ranges for 'neutral co-ligand' values. Moreover the bridging species data often depend on corrections for the effects of electronically-active co-ligands such as cyclopentadienyl-like groups. The derived neutral co-ligand estimates, ν(NO)*, are: (a) twofold bridged nitrosyls with a metal-metal bond order of one, or greater than one, absorb at ca. 1610-1490 cm(-1); (b) twofold bridged nitrosyl ligands with a longer non-bonding M⋯M distance, ca. 1520-1490 cm(-1); (c) threefold bridged nitrosyls, ca. 1470-1410 cm(-1); (d) σ/π dihaptonitrosyl, [M(η2-NO)], where M=Cr, Mn and Ni; ca. 1490-1440 cm(-1). Isonitrosyls, from few examples, appear to absorb below ca. 1100 cm(-1). To be published DFT calculations of the infrared and Raman spectra of complexes with formulae [M(NO)4-n(CO)n] (M=Cr, Mn, Fe, Co, Ni, and n=0, 1, 2, 3, 4, respectively) are used as models for the assignments of the ν(MN) and δ(MNO) bands from more complex metal nitrosyls.

Millimeter-wave spectroscopy of CoNO produced by UV laser photolysis of Co(CO)3NO

The rotational spectrum of cobalt mononitrosyl (CoNO) produced by ultraviolet photolysis of Co(CO)(3)NO was observed in the millimeter-wave region. Seven rotational transitions in the ground state ranging from J = 6-5 to 12-11, with hyperfine splittings due to the Co nucleus (I = 7/2), were detected in a supersonic jet environment, while higher-frequency transitions in the range from J = 29-28 to 35-34 were measured in the ground, nu(1), nu(2), nu(3), and 2nu(2) vibrational states using a free-space absorption cell. It was confirmed from the observed spectral pattern that the CoNO molecule has a linear structure with the electronic ground state of (1)Sigma(+) symmetry. The rotational lines in the 2nu(2)(Sigma) and nu(3) states were observed to be perturbed by Fermi resonance. The equilibrium rotational constant B(e) is determined to be 4682.207(15) MHz. The CoN bond length is derived to be 1.5842 A assuming the NO bond length of 1.1823 A. A large nuclear spin-rotation interaction constant, C(I) = 123.8(11) kHz, was determined, suggesting a (1)Pi electronic excited state lying close to the ground state.

Thermochemistry, bonding, and reactivity of Ni+ and Ni2+ in the gas phase

In this review, we present a general overview on the studies carried out on Ni(+-)- and Ni(2+)-containing systems in the gas phase since 1996. We have focused our attention in the determination of binding energies in parallel with an analysis of the structure and bonding of the complexes formed by the interaction of Ni(+) with one ligand, or in clusters where this metal ion binds several identical or different ligands. Solvation of Ni(2+) by different ligands is also discussed, together with the theoretical information available of doubly charged Ni-containing species. The final section of this review is devoted to an analysis of the gas-phase uni- and bimolecular reactivity of Ni(+) and Ni(2+) complexes.

Dissociative and associative attachment of NO to iron clusters

Electronic and geometrical structures of iron clusters with associative (FeNO, Fe2NO, Fe3NO, Fe4NO, Fe5NO, and Fe6NO) and dissociative (OFeN, OFe2N, OFe3N, OFe4N, OFe5N, and OFe6N) attachments of NO, as well as the corresponding singly negatively and positively charged ions, are computed using density functional theory with generalized gradient corrections. Both types of isomers are found to be stable and no spontaneous dissociation was observed during the geometry optimizations. The ground states correspond to dissociative attachment of NO for all iron clusters Fe(n), except for Fe and Fe+. All of the OFe(n)N clusters have ferrimagnetic ground states, except for OFe2N, OFe2N-, OFe4N, and OFe4N-, which prefer the ferromagnetic coupling. In the ferrimagnetic states, the excess spin density at one iron atom couples antiferromagnetically to the excess spin densities of all other iron atoms. Relative to the high-spin Fe(n) ground state, the lowest energy ferrimagnetic state quenches the total magnetic moments of iron clusters by 7, which is to be compared with a reduction in the magnetic moment of one in the lowest energy ferromagnetic states. Dissociation of NO on the iron clusters has a pronounced impact on the energetics of reactions; the Fe(n)NO+CO-->Fe(n)N+CO2 channels are exothermic while the OFe6N+CO--> Fe6N+CO2 channels are nearly thermoneutral.

Density Functional Study of the Electronic Structure and Related Properties of Pt(NO)/Pt(NO2) Redox Couples

Density functional calculations at the B3LYP level of theory, using the SDD basis set, provide satisfactory description of geometric, energetic, electronic and spectroscopic properties of the Pt(NO)/Pt(NO2) redox couple. The neutral Pt(NO) species adopts a bent 2A' ground state, while the cationic [Pt(NO)]+ species adopts a linear 1Σ+ ground state. The B3LYP/SDD- predicted Pt-N bond lengths are 2.016 and 1.777 Å for Pt(NO) (2A') and [Pt(NO)]+ (1Σ+), respectively, while the ∠Pt-N-O bent angle for [Pt(NO)] (2A') is 119.6°. On the other hand, the anionic [Pt(NO)]- species adopts the bent 1A' ground state with a Pt-N bond length of 1.867 Å and a ∠Pt-N-O bent angle of 122.5°. The computed binding energies of the NO, NO+ and NO- ligands with Pt(0) were found to be 29.9 (32.8), 69.9 (78.4) and 127.4 (128.7) kcal/mol at the B3LYP/SDD and CCSD(T)/SDD (numbers in parentheses) levels of theory, respectively. Moreover, the structure of the [Pt(NO2)]+ component of the Pt(NO)/Pt(NO2) redox couple and its transformation to [Pt(NO)]+ upon reaction with CO was analysed in the framework of the DFT theory. The coordination of the CO ligand to [Pt(NO2)]+ affords the cationic mixed-ligand [Pt(CO)(NO2)]+ complex, which is stabilized by 66.6 (60.5) kcal/mol, with respect to the separated [Pt(NO2)]+ and CO in their ground states. The O-transfer reaction from the coordinated NO2 to the coordinated CO ligands in the presence of the [Pt(NO2)]+ species corresponds to an exothermic process; the heat of the reaction (∆RH) is -85.2 (-80.5) kcal/mol and the activation barrier amounts to 27.7 (33.0) kcal/mol. Finally, the equilibrium structures of selected stationary points related to the transformation of NO to NO2 ligand located on the potential energy surfaces of the [Pt(NO),O2], [Pt(NO)+,O2], and [Pt(NO)-,O2] systems were analysed in the framework of the DFT theory. The computed interaction energies of O2 with Pt(NO), [Pt(NO)]+ and [Pt(NO)]- species were found to be 106.9 (105.3), 49.2 (48.4) and 26.9 (26.5) kcal/mol, respectively. The O2 ligand is coordinated to the Pt central atom in an end-on mode for [Pt(NO),O2] and [Pt(NO)-,O2] systems and in a side-on mode for the [Pt(NO)+,O2] system. The transformation of NO to NO2 in [Pt(NO)]- species upon reaction with dioxygen corresponds to an exothermic process; the heat of the reaction (∆RH) is -60.6 (-55.8) kcal/mol, while the activation barrier amounts to 35.5 (30.2) kcal/mol. Calculated structures, relative stability and bonding properties of all stationary points are discussed with respect to computed electronic and spectroscopic properties, such as charge density distribution and harmonic vibrational frequencies.

Spectroscopic and theoretical investigations of vibrational frequencies in binary unsaturated transition-metal carbonyl cations, neutrals, and anions

Figure 18 presents the C-O stretching vibrational frequencies of the first-row transition-metal monocarbonyl cations, neutrals, and anions in solid neon; similar diagrams have been reported for neutral MCO species in solid argon, but three of the early assignments have been changed by recent work and one new assignment added. The laser-ablation method produces mostly neutral atoms with a few percent cations and electrons for capture to make anions; in contrast, thermal evaporation gives only neutral species. Hence, the very recent neon matrix investigations in our laboratory provide carbonyl cations and anions for comparison to neutrals on a level playing field. Several trends are very interesting. First, for all metals, the C-O stretching frequencies follow the order cations > neutrals > anions with large diagnostic 100-200 cm-1 separations, which is consistent with the magnitude of the metal d to CO pi * donation. Second, for a given charge, there is a general increase in C-O stretching vibrational frequencies with increasing metal atomic number, which demonstrates the expected decrease in the metal to CO pi * donation with increasing metal ionization potential. Some of the structure in this plot arises from the extra stability of the filled and half-filled d shell and from the electron pairing that occurs at the middle of the TM row; the plot resembles the "double-humped" graph found for the variation in properties across a row of transition metals. For the anions, the variation with metal atom is the smallest since all of the metals can easily donate charge to the CO ligand. Third, for the early transition-metal Ti, V, and Cr families, the C-O stretching frequencies decrease when going down the family, but the reverse relationship is observed for the late transition-metal Fe, Co, and Ni families. In most of the present discussion, we have referred to neon matrix frequencies; however, the argon matrix frequencies are complementary, and useful information can be obtained from comparison of the two matrix hosts. In most cases, the neon-to-argon red shift for neutral carbonyls is from 11 to 26 cm-1, but a few (CrCO) lie outside of this range. In the case of FeCO and Fe(CO)2, it appears that neon and argon trap different low-lying electronic states. In general, the carbonyl neutrals and anions have similar shifts but carbonyl cations have larger matrix shifts. For example, the FeCO+ fundamental is at 2123.0 cm-1 in neon and 2081.5 cm-1 in argon, a 42.5 cm-1 shift, which is larger than those found for FeCO- (11.7 cm-1) and FeCO (11.7 cm-1). It is unusual for different low-lying electronic states to be trapped in different matrices, but CUO provides another example. The linear singlet state (1047.3, 872.2 cm-1) is trapped in solid neon, and a calculated 1.2 kcal/mol higher triplet state is trapped in solid argon (852.5, 804.3 cm-1) and stabilized by a specific interaction with argon. The bonding trends are well described by theoretical calculations of vibrational frequencies. Table 5 compares the scale factors (observed neon matrix/calculated) for the C-O stretching modes of the monocarbonyl cations, neutrals, and anions of the first-row transition metals observed in a neon matrix using the B3LYP and BP86 density functionals. Most of the calculated carbonyl harmonic stretching frequencies are within 1% of the experimental fundamentals at the BP86 level of theory, while calculations using the B3LYP functional give frequencies that are 3-4% higher as expected for these density functionals and calculations on saturated TM-carbonyls. For second- and third-row carbonyls using the BP86 density functional and the LANL effective core potential in conjunction with the DZ basis set, the agreement between theory and experiment is just as good. For example, the 16 M(CO)1-4 neutral and anion and 2 MCO+ cation (M = Ru, Os) carbonyl frequencies are fit within 1.5%. The 16 species (M = Rh, Ir) are fit within 1%, but the Rh(CO)1-4+ calculations are 2-3% too low and Ir(CO)1-4+ computations are 1-2% too low. In addition to predicting the vibrational frequencies, DFT can be used to calculate different isotopic frequencies, and isotopic frequency ratios can be computed as a measure of the normal vibrational mode in the molecule for an additional diagnostic. For diatomic CO, the 12CO/13CO ratio 1.0225 and C16O/C18O ratio 1.0244 characterize a pure C-O stretching mode. In a series of molecules such as RhCO+, RhCO, and RhCO-, where the metal-CO bonding varies, the Rh-C, C-O vibrational interaction is different and the unique isotopic ratios for the carbonyl vibration are characteristic of that particular molecule. Table 6 summarizes the isotopic ratios observed and calculated for the RhCO+,0,- species. Note that RhCO+ exhibits slightly more carbon-13 and less oxygen-18 involvement in the C-O vibration than CO itself and that this trend increases to RhCO and to RhCO- as the Rh-C bond becomes shorter and stronger. Note also how closely the calculated and observed ratios both follow this trend. In a molecule with two C-O stretching modes, for example, bent Ni(CO)2 exhibits a strong b2 mode at 1978.9 cm-1 and a weak a1 mode at 2089.7 cm-1 in solid neon, and these two modes involve different C and O participations. The symmetric mode shows substantially more C (1.0242) and less O (1.0217) participation than does the antisymmetric mode with C (1.0228) and O (1.0238) involvement, based on the given isotopic frequency ratios, which are nicely matched by DFT calculations (a1 1.0244, 1.0224 and b2 1.0232, 1.0241, respectively). These investigations of vibrational frequencies in unsaturated transition-metal carbonyl cations, neutrals, and anions clearly demonstrate the value of a close working relationship between experiment and theory to identify and characterize new molecular species.

Infrared spectrum of the hyponitrite dianion, N(2)O(2)2-, isolated and insulated from stabilizing metal cations in solid argon

Ultraviolet irradiation of a rigid 7 K argon matrix containing alkali or alkaline earth metal atoms and NO(2) isolated from each other by one or two layers of argon forms N(2)O(2)2-dianions insulated from two M(+) cations by argon atoms, and visible photolysis reverses this electron-transfer process likely involving the N(2)O(2)(-) anion intermediate. The isolated N(2)O(2)2- dianion is identified from isotopic substitution and isotopic mixtures, which show that the new 1028.5 cm(-1) metal independent absorption involves two equivalent NO subunits. DFT calculations predict a strong 1078.1 cm(-1) fundamental for the Li(NO)(2)Li molecule and isotopic frequency ratios in excellent agreement with the observed values, which provides a model for the matrix dianion system. The spectrum of solid Na(2)N(2)O(2) exhibits a 1030 cm(-1) infrared band, which strongly supports the present N(2)O(2)2- dianion assignment. The electrostatic stabilization of N(2)O(2)2-, which is probably unstable in the gas phase, is made possible by metal cations separated by one or two insulating layers of argon in the rigid 7 K matrix.