Transition Metal Carbonyl Complexes Research Articles

The hapticity of octafluorocyclooctatetraene in its first-row mononuclear transition metal carbonyl complexes: effect of perfluorination

The iron tricarbonyl complex of octafluorocyclooctatetraene was synthesized by Hughes and co-workers and shown by X-ray crystallography to have a trihapto–monohapto structure (η3,1-C8F8)Fe(CO)3 in contrast to the tetrahapto structure (η4-C8H8)Fe(CO)3 formed by the non-fluorinated cyclooctatetraene. This difference has stimulated a comprehensive density functional theoretical study of the octafluorocyclooctatetraene metal carbonyl complexes (C8F8)M(CO)n (n = 4, 3, 2, 1 for M = Ti, V, Cr, Mn, and Fe; n = 3, 2, 1 for M = Co, Ni) for comparison with their hydrogen analogues (C8H8)M(CO)n. In most such systems, the substitution of fluorine for hydrogen leads to relatively small changes in the preferred structures. However, for the iron carbonyl derivatives (C8X8)Fe(CO)3 (X = H, F), the difference observed experimentally has been confirmed by theory with (η3,1-C8F8)Fe(CO)3 and (η4-C8H8)Fe(CO)3 being the lowest energy structures by 4 and 14 kcal/mol, respectively. The ligand exchange reactions C8H8 + (C8F8)M(CO)n → C8F8 + (C8H8)M(CO)n are predicted to be exothermic for almost all of the systems considered, with the (η3,1-C8X8)Fe(CO)3 system being the main exception. This suggests that the C8F8 ligand generally bonds more weakly to transition metals than the C8H8 ligand in accord with the electron-withdrawing effect of the ligand fluorine atoms.

Spectroscopic and Electrochemical Studies of Group 6 and 8 Transition Metal Carbonyl Derivatives of tris{(diphenylphosphinomethyl)dimethylsilyl}methane

A new series of transition metal carbonyl complexes of tris{(diphenylphosphinomethyl)dimethylsilyl}methane are described in this work. Treatment of M(CO)6 (M = Cr, W, Mo) and Fe2(CO)9 with [(Ph2PCH2Me2Si)3CH] in tetrahydrofuran at elevated temperature resulted in the isolation of [M(CO)3{(Ph2PCH2Me2Si)3CH}] (M = Cr(1), Mo(2), W(3), Fe(4)) in good yield. These complexes have been characterized by elemental analysis, conductivity measurements, mass spectrometry, with IR, electronic, 1H and 31P NMR spectroscopy, and cyclic voltammetry. The data suggest that complexes 1, 2, 3, and 4 have octahedral geometry around the metal atom with tridentate coordination of the ligand. Electrochemical studies of 1, 2, 3, and 4 using cyclic voltammetry indicate quasireversible metal centered oxidation (E°/ −1.217 V(1), −1.218 V(2), −1.166 V(3), and −1.258 V(4) versus Ag/Ag+) and ligand reductions (0.292 V, 0.170 V, −0.331 V, and 0.338 V versus Ag/Ag+).

Principles, Performance, and Applications of Spectral Reconstitution (SR) in Quantitative Analysis of Oils by Fourier Transform Infrared Spectroscopy (FT-IR)

Spectral reconstitution (SR) is a dilution technique developed to facilitate the rapid, automated, and quantitative analysis of viscous oil samples by Fourier transform infrared spectroscopy (FT-IR). This technique involves determining the dilution factor through measurement of an absorption band of a suitable spectral marker added to the diluent, and then spectrally removing the diluent from the sample and multiplying the resulting spectrum to compensate for the effect of dilution on the band intensities. The facsimile spectrum of the neat oil thus obtained can then be qualitatively or quantitatively analyzed for the parameter(s) of interest. The quantitative performance of the SR technique was examined with two transition-metal carbonyl complexes as spectral markers, chromium hexacarbonyl and methylcyclopentadienyl manganese tricarbonyl. The estimation of the volume fraction (VF) of the diluent in a model system, consisting of canola oil diluted to various extents with odorless mineral spirits, served as the basis for assessment of these markers. The relationship between the VF estimates and the true volume fraction (VF(t)) was found to be strongly dependent on the dilution ratio and also depended, to a lesser extent, on the spectral resolution. These dependences are attributable to the effect of changes in matrix polarity on the bandwidth of the ν(CO) marker bands. Excellent VF(t) estimates were obtained by making a polarity correction devised with a variance-spectrum-delineated correction equation. In the absence of such a correction, SR was shown to introduce only a minor and constant bias, provided that polarity differences among all the diluted samples analyzed were minimal. This bias can be built into the calibration of a quantitative FT-IR analytical method by subjecting appropriate calibration standards to the same SR procedure as the samples to be analyzed. The primary purpose of the SR technique is to simplify preparation of diluted samples such that only approximate proportions need to be adhered to, rather than using exact weights or volumes, the marker accounting for minor variations. Additional applications discussed include the use of the SR technique in extraction-based, quantitative, automated FT-IR methods for the determination of moisture, acid number, and base number in lubricating oils, as well as of moisture content in edible oils.

Carbonyl complexes of transition metals with stabilized germylenes

Germylenes based on substituted diethylenetriamine (1), diethanolamines (2, 3) and pyridine-containing dialcohols (4, 5) were used as ligands in molybdenum and tungsten carbonyl complexes. Synthesis of new mono- and disubstituted (cis- or trans-) germanium(II) containing molybdenum (8, 9, 14, 15, 17) and tungsten (6, 7, 10–13, 16) carbonyl complexes were described. Composition of the complexes obtained was established by elemental analysis data and their structures were investigated by multinuclear NMR spectroscopy, IR and X-ray diffraction analysis (7, 13 and 17). The germylenes based on dialkanolamines and pyridine-containing dialcohols (O-ligands) give cis-digermanium complexes in contrast to the germylenes based on diethylenetriamines (N-ligands) which form trans-digermanium complexes.

Synthesis and Characterization of Stable Hetereocyclic (Schiff Base) Divalent Tin Species and Photogeneration of Their Transition Metal Carbonyl Complexes

New stable divalent heterocyclic species [SnL1; 1, SnL2; 2] using ONNO and SNNS tetradentate Schiff bases; N,N′-bis(salicylidene)-1,2-bis(o-aminophenoxy)ethane (H2L1) and N,N′-bis(2-aminothiophenol)-1,4-bis(2-carboxaldehydephenoxy)butane (H2L2) were obtained in good yields by alcolysis of the M-N bonds of the divalent precursor Sn[N(SiMe3)2]2 by diols. They have been isolated as solids at ambient temperature and are monomeric. FT-IR, 1H and 119Sn-NMR spectra are suggestive of N … M intramolecular coordination. Then the synthesis and characterization of the new stable mono and cis-disubstituted Sn(II) chromium and tungsten carbonyl complexes [L1Sn]M(CO)5 (M= Cr, 3; W, 4); [L2Sn]M(CO)5 (M= Cr, 5; W, 6); cis-[L1Sn]2M(CO)4 (M= Cr, 7; W, 8) and cis-[L2Sn]2M(CO)4 (M= Cr, 9; W, 10) are described. Pentacarbonyl complexes (3–6) were obtained in high yields by treatment of the M(CO)5THF (M= Cr, W) intermediates with the divalent species [SnL1; 1, SnL2; 2] and tetracarbonyl complexes (7–10) were synthesized by the photochemical reactions of [LnSn]M(CO)5 with [LnSn] (n = 1, 2). Each of the new carbonyl complexes has been characterized by IR, 1H, 13C, 119Sn-NMR spectroscopy, and mass spectrometry. The sigma donor and pi acceptor ability of the divalent tin species [SnL1, 1; SnL2, 2] as ligands in the transition metal carbonyl complexes (3–10) is discussed by comparing ν(CO) stretching frequencies.

Benchmark calculations of metal carbonyl cations: relativistic vs. electron correlation effects

In this paper we present benchmark results for isoelectronic metal carbonyl complexes of the groups 11 and 12 of the periodic table. The focus is on the geometry, vibrational frequencies, bond dissociation energy and chemical bonding. The description of these complexes requires a good balance between electron correlation and relativistic effects. Our results demonstrate that the combination of the effective core potential and the MP2 method gives quantitative results for the first- and the second-row transition metal complexes and only qualitative agreement for the third-row complexes. In order to obtain quantitative results for the whole series the use of four-component or X2C methods is mandatory. The fourth-row transition metal carbonyl complexes from groups 11 and 12 have been studied for the first time. The metal-carbon bond strength pattern along the group is shown to be highly dependent on the correct description of the relativistic effects. Finally, the relativistic effects on the bonding are studied by means of electron density difference maps, the analysis of the bond critical points of the electron density and the mechanism for σ-donation and π-backdonation. Our analysis indicates that the fourth-row complexes exhibit a strong covalent character induced by relativistic effects.

Comparisons of 2D IR measured spectral diffusion in rotating frames using pulse shaping and in the stationary frame using the standard method

Multidimensional visible spectroscopy using pulse shaping to produce pulses with stable controllable phases and delays has emerged as an elegant tool to acquire electronic spectra faster and with greatly reduced instrumental and data processing errors. Recent migration of this approach using acousto-optic modulator (AOM) pulse shaping to the mid-infrared region has proved useful for acquiring two dimensional infrared (2D IR) vibrational echo spectra. The measurement of spectral diffusion in 2D IR experiments hinges on obtaining accurate 2D line shapes. To date, pulse shaping 2D IR has not been used to study the time-dependent spectral diffusion of a vibrational chromophore. Here we compare the spectral diffusion data obtained from a standard non-collinear 2D IR spectrometer using delay lines to the data obtained from an AOM pulse shaper based 2D IR spectrometer. The pulse shaping experiments are performed in stationary, partially rotating, and fully rotating reference frames and are the first in the infrared to produce 2D spectra collected in a fully rotating frame using a phase controlled pulse sequence. Rotating frame experiments provide a dramatic reduction in the number of time points that must be measured to obtain a 2D IR spectrum, with the fully rotating frame giving the greatest reduction. Experiments were conducted on the transition metal carbonyl complex tricarbonylchloro(1,10-phenanthroline)rhenium(I) in chloroform. The time dependent data obtained from the different techniques and with different reference frames are shown to be in agreement.

A role for reactive oxygen species in the antibacterial properties of carbon monoxide-releasing molecules

Carbon monoxide-releasing molecules (CO-RMs) are, in general, transition metal carbonyl complexes that liberate controlled amounts of CO. In animal models, CO-RMs have been shown to reduce myocardial ischaemia, inflammation and vascular dysfunction, and to provide a protective effect in organ transplantation. Moreover, CO-RMs are bactericides that kill both Gram-positive and Gram-negative bacteria such as Staphylococcus aureus and Pseudomonas aeruginosa. Herein are reviewed the microbial genetic and biochemical responses associated with CO-RM-mediated cell death. Particular emphasis is given to the data revealing that CO-RMs induce the generation of reactive oxygen species (ROS), which contribute to the antibacterial activity of these compounds.

Rapid Synthesis of Radioactive Transition-Metal Carbonyl Complexes at Ambient Conditions

Carbonyl complexes of radioactive transition metals can be easily synthesized with high yields by stopping nuclear fission or fusion products in a gas volume containing CO. Here, we focus on Mo, W, and Os complexes. The reaction takes place at pressures of around 1 bar at room temperature, i.e., at conditions that are easy to accommodate. The formed complexes are highly volatile. They can thus be transported within a gas stream without major losses to setups for their further investigation or direct use. The rapid synthesis holds promise for radiochemical purposes and will be useful for studying, e.g., chemical properties of superheavy elements.

Formation of uncapped nanometre-sized metal particles by decomposition of metal carbonyls in carbon nanotubes

Carbonyl complexes of transition metals (Mx(CO)y, where x = 1, 2, or 3 and y = 6, 10, or 12 for M = W, Re, or Os, respectively) inserted into single walled carbon nanotubes (SWNT, diameter 1.5 nm) transform into metallic nanoparticles (MNPs) under heat treatment or electron beam irradiation. The host-nanotube acts as an efficient template, controlling the growth of MNPs to ∼1 nm in diameter. The only co-product of nanoparticle formation, carbon monoxide (CO) gas, creates pockets of high pressure between nanoparticles, thus preventing their collision and coalescence into larger structures. As a result, the MNPs stay largely spheroidal in shape and are uniformly distributed throughout the entire length of the SWNT. Despite their extremely small size (on average each MNP contains 30–90 atoms) and no protection of their surface by a capping layer of molecules, the metallic nanoparticles encapsulated in nanotubes are very stable under ambient conditions and even at elevated temperatures. Aberration-corrected high-resolution transmission electron microscopy reveals the crystalline nature of the MNPs, probes their interactions with the nanotube interior and illustrates the complex dynamics of confined MNPs in real-time and direct-space.

Quantum Cascade Laser Spectroscopy and Photoinduced Chemistry of Al–(CO)n Clusters in Helium Nanodroplets

Helium nanodroplet isolation and a tunable quantum cascade laser are used to probe the fundamental CO stretch bands of aluminum carbonyl complexes, Al-(CO)(n) (n ≤ 5). The droplets are doped with single aluminum atoms via the resistive heating of an aluminum wetted tantalum wire. The downstream sequential pick-up of CO molecules leads to the rapid formation and cooling of Al-(CO)(n) clusters within the droplets. Near 1900 cm(-1), rotational fine structure is resolved in bands that are assigned to the CO stretch of a linear (2)Π(1/2) Al-CO species and the asymmetric and symmetric CO stretch vibrations of a planar C(2v) Al-(CO)(2) complex in a (2)B(1) electronic state. Bands corresponding to clusters with n ≥ 3 lack resolved rotational fine structure; nevertheless, the small frequency shifts from the n = 2 bands indicate that these clusters consist of an Al-(CO)(2) core with additional CO molecules attached via van der Waals interactions. A second n = 2 band is observed near the CO stretch of Al-CO, indicating a local minimum on the n = 2 potential consisting of an "unreacted" (Al-CO)-CO cluster. The line width of this band is ∼0.3 cm(-1), which is about 30 times broader than the transitions within the Al-CO band. The additional broadening is consistent with a homogeneous mechanism corresponding to a rapid vibrational excitation induced reaction within the (Al-CO)-CO cluster to form the covalently bonded Al-(CO)(2) complex. Ab initio CCSD(T) calculations and natural bond orbital (NBO) analyses are carried out to investigate the nature of the bonding in the n = 1, 2 complexes. The NBO calculations show that both π-donation (from the occupied aluminum p orbital into a π* antibonding CO orbital) and σ-donation (from CO into the empty aluminum p orbitals) play a significant role in the bonding, analogous to transition-metal carbonyl complexes. The large red shift observed for the CO stretch vibrations is consistent with this bonding analysis.

Carbon Monoxide-Releasing Micelles for Immunotherapy

With the discovery of important biological roles of carbon monoxide (CO), the use of this gas as a therapeutic agent has attracted attention. However, the medical application of this gas has been hampered by the complexity of the administration method. To overcome this problem, several transition-metal carbonyl complexes, such as Ru(CO)(3)Cl(glycinate), [Ru(CO)(3)Cl(2)](2), and Fe(η(4)-2-pyrone)(CO)(3), have been used as CO-releasing molecules both in vitro and in vivo. We sought to develop micellar forms of metal carbonyl complexes that would display slowed diffusion in tissues and thus better ability to target distal tissue drainage sites. Specifically, we aimed to develop a new CO-delivery system using a polymeric micelle having a Ru(CO)(3)Cl(amino acidate) structure as a CO-releasing segment. The CO-releasing micelles were prepared from triblock copolymers composed of a hydrophilic poly(ethylene glycol) block, a poly(ornithine acrylamide) block bearing Ru(CO)(3)Cl(ornithinate) moieties, and a hydrophobic poly(n-butylacrylamide) block. The polymers formed spherical micelles in the range of 30-40 nm in hydrodynamic diameter. Further characterization revealed the high CO-loading capacity of the micelles. CO-release studies showed that the micelles were stable in physiological buffer and serum and released CO in response to thiol-containing compounds such as cysteine. The CO release of the micelles was slower than that of Ru(CO)(3)Cl(glycinate). In addition, the CO-releasing micelles efficiently attenuated the lipopolysaccharide-induced NF-κB activation of human monocytes, while Ru(CO)(3)Cl(glycinate) did not show any beneficial effects. Moreover, cell viability assays revealed that the micelles significantly reduced the cytotoxicity of the Ru(CO)(3)Cl(amino acidate) moiety. This novel CO-delivery system based on CO-releasing micelles may be useful for therapeutic applications of CO.

Transition metals in the synthesis of complex organic molecules

Formalisms, Electron Counting, Bonding (How Things Work) Organometallic Reaction Mechanisms Synthetic Applications of Transition Metal Hybrides, Homogeneous Hydrogenation Synthetic Applications of Complexes Containing Metal-Carbon alpha-Bonds Synthetic Applications of Transition Metal Carbonyl Complexes Synthetic Applications of Transition Metal Carbene Complexes Synthetic Applications of Transition Metal Alkene, Diene, and Dienyl Complexes Synthetic Applications of Transition Metal Alkyne Complexes Synthetic Applications of n3 Allyl Transition Metal Complexes Synthetic Application of Transition Metal Arene Complexes.

Zinc (0) chemistry: does the missing 18-electron zinc tricarbonyl really exist?

Recently, a combined laser ablation and density functional theory study (Jiang and Xu, J. Am. Chem. Soc. 2005, 127, 8906) claimed the existence of the long-sought 18-electron member of the first-row transition metal carbonyl complex, Zn(CO)(3). In this paper, we systematically investigate the thermodynamic and kinetic stability of Zn(CO)(3) towards CO-extrusion at the BP86, B3PW91, BPW91, PBEPBE, BH&HLYP, B3LYP, MP2, MP4SDQ, QCISD, CCSD and CASPT2 levels as well as the Born-Oppenheimer molecular dynamic (BOMD) simulation. All these calculations consistently reveal that the 18e Zn(0) complex Zn(CO)(3) is neither a genuine minimum point nor kinetically stable with negligibly low barriers. In particular, Zn(CO)(3) is quite thermodynamically unstable with respect to the fragments (1)Zn + 3CO by around 40 kcal mol(-1) at all the three sophisticated correlation levels, i.e., MP4SDQ, QCISD and CCSD. We thus conclude that the tricarbonyl Zn(0) complex, Zn(CO)(3), should not exist even for spectroscopic characterization. Interestingly, our extensive structural search predicts that two triplet di-zinc carbonyls, i.e., (3)(CO)ZnZn and (3)(CO)(2)ZnZn, have noticeable kinetic stability (10.41 and 8.11 kcal mol(-1) at the CCSD level) against the respective CO- and Zn-extrusion, which can be compared with the value 8.70 kcal mol(-1) for the already detected (3)Zn(CO)(2) (Jiang and Xu, J. Phys. Chem. A2006,110, 7092). Our designed (3)(CO)ZnZn and (3)(CO)(2)ZnZn together with the experimentally known (3)ZnCO and (3)Zn(CO)(2) are formally associated with the zinc (0) "spin-based zinc carbonyls" and should be considered as remarkable, since most of the known zinc complexes usually contain +2 or +1 oxidation state Zn.

The hapticity of cyclooctatetraene in its first row mononuclear transition metal carbonyl complexes: Several examples of octahapto coordination

The two cyclooctatetraene metal carbonyls that have been synthesized are the tetrahapto derivative (η 4-C 8H 8)Fe(CO) 3 and the hexahapto derivative (η 6-C 8H 8)Cr(CO) 3 using the reactions of cyclooctatetraene with Fe(CO) 5 and with fac-(CH 3CN) 3Cr(CO) 3, respectively. Related C 8H 8M(CO) n (M = Ti, V, Cr, Mn, Fe, Co, Ni; n = 4, 3, 2, 1) species have now been investigated by density functional theory in order to explore the scope of cyclooctatetraene metal carbonyl chemistry. In this connection, the existence of octahapto (η 8-C 8H 8)M(CO) n species is predicted as long as the central metal M does not exceed the 18-electron configuration by receiving eight electrons from the η 8-C 8H 8 ring. Thus the lowest energy structures (η 8-C 8H 8)Ti(CO) n ( n = 3, 2, 1), (η 8-C 8H 8)M(CO) n (M = V, Cr; n = 2, 1), and (η 8-C 8H 8)Mn(CO) all have octahapto η 8-C 8H 8 rings. An exception is (η 6-C 8H 8)Fe(CO), with a hexahapto η 6-C 8H 8 ring and thus only a 16-electron configuration for the iron atom. Hexahapto (η 6-C 8H 8)M(CO) n structures are predicted for the known (η 6-C 8H 8)Cr(CO) 3 as well as the unknown (η 6-C 8H 8)Ti(CO) 4, (η 6-C 8H 8)V(CO) 3, (η 6-C 8H 8)Mn(CO) 2, and (η 6-C 8H 8)Fe(CO) 2 with 18, 18, 17, 17, and 18 electron configurations, respectively, for the central metal atoms. There are two types of tetrahapto C 8H 8M(CO) n complexes. In the 1,2,3,4-tetrahapto (η 4-C 8H 8)M(CO) n complexes two adjacent C C double bonds, forming a 1,3-diene unit similar to butadiene, are bonded to the metal atom. In the 1,2,5,6-tetrahapto (η 2,2-C 8H 8)M(CO) 3 derivatives two non-adjacent C C double bonds of the C 8H 8 ring are bonded to the metal atom. The known (η 4-C 8H 8)Fe(CO) 3 is a 1,2,3,4-tetrahapto complex. The unknown isomeric 1,2,5,6-tetrahapto complex (η 2,2-C 8H 8)Fe(CO) 3 is predicted to lie ∼15 kcal/mol above (η 4-C 8H 8)Fe(CO) 3. The related 1,2,5,6-tetrahapto complexes (η 2,2-C 8H 8)Cr(CO) 4, (η 2,2-C 8H 8)Mn(CO) 4, [(η 2,2-C 8H 8)Mn(CO) 3] −, (η 2,2-C 8H 8)Co(CO) 2, and (η 2,2-C 8H 8)Ni(CO) 2 are all predicted to be low-energy structures.

Complexes of Four‐Membered Group 13 Metal(I) N‐Heterocyclic Carbene Analogues with Metal Carbonyl Fragments

AbstractThe four‐membered gallium(I) and indium(I) heterocycles, [:M(Giso)] (M = Ga or In; Giso = {[N(Ar)]2CN(C6H11)2}–, Ar = C6H3iPr2‐2,6), were treated with a series of transition metal carbonyl complexes. These reactions afforded the complexes [Fe(CO)4{Ga(Giso)}], [(CO)3Co{μ‐Ga(Giso)}2Co(CO)3], [Ru(CO)2(PPh3)2{M(Giso)}] and [CpMo(CO)2{[(Giso)Ga]2OH}], which were crystallographically and/or spectroscopically characterized. The results of the study show that the two heterocycles can act as σ‐donor ligands, but they are not as nucleophilic as, for example, group 13 diyls, :MR (M = Ga or In; R = alkyl, aryl, etc.). In addition, the degree of π‐back‐bonding in their metal carbonyl complexes does not appear to be significant.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Polarizability effect in transition metal carbonyl complexes

The literature date on substituent influence on the carbonyl stretching frequencies (ν), CO stretching force constants (k), as well as 13C NMR carbonyl chemical shifts (δ) have been analyzed for 19 series of the transition metal carbonyl complexes. It was established for the first time that the ν, k and δ values depend not only on the inductive and resonance effects but also on the polarizability of substituents. The polarizability contribution ranges up to 37%.

DFT tests for group 8 transition metal carbonyl complexes

The applicability of several popular density functionals in predicting the geometrical parameters and energetics of transition metal carbonyl complexes of iron, ruthenium and osmium has been studied. The methods tested include pure GGA functionals (BLYP, BP86, OPBE, HCTH, PBE, VSXC) and hybrid GGA functionals (B3PW91, B3LYP, PBE1PBE, MPW1K, B97-2, B1B95, PBE1KCIS). The effect of changing the metal basis set from Huzinaga's all-electron basis to SDD scECP basis was also studied. The results show, that hybrid functionals are needed in order to describe the back-bonding ability of the carbonyl ligands as well as to deal with metal-metal bonds. The best general performance, when also the computational cost was considered, was obtained with hybrid functionals B3PW91 and PBE1PBE, which therefore provide an efficient tool for solving problems involving large or medium sized transition metal carbonyl compounds.

DFT calculations of 1H and 13C NMR chemical shifts in transition metal hydrides

Transition metal hydrides are of great interest in chemistry because of their reactivity and their potential use as catalysts for hydrogenation. Among other available techniques, structural properties in transition metal (TM) complexes are often probed by NMR spectroscopy. In this paper we will show that it is possible to establish a viable methodological strategy in the context of density functional theory, that allows the determination of 1H NMR chemical shifts of hydride ligands attached to transition metal atoms in mononuclear systems and clusters with good accuracy with respect to experiment. 13C chemical shifts have also been considered in some cases. We have studied mononuclear ruthenium complexes such as Ru(L)(H)(dppm)2 with L = H or Cl, cationic complex [Ru(H)(H2O)(dppm)2]+ and Ru(H)2(dppm)(PPh3)2, in which hydride ligands are characterized by a negative 1H NMR chemical shift. For these complexes all calculations are in relatively good agreement compared to experimental data with errors not exceeding 20% except for the hydrogen atom in Ru(H)2(dppm)(PPh3)2. For this last complex, the relative error increases to 30%, probably owing to the necessity to take into account dynamical effects of phenyl groups. Carbonyl ligands are often encountered in coordination chemistry. Specific issues arise when calculating 1H or 13C NMR chemical shifts in TM carbonyl complexes. Indeed, while errors of 10 to 20% with respect to experiment are often considered good in the framework of density functional theory, this difference in the case of mononuclear carbonyl complexes culminates to 80%: results obtained with all-electron calculations are overall in very satisfactory agreement with experiment, the error in this case does not exceed 11% contrary to effective core potentials (ECPs) calculations which yield errors always larger than 20%. We conclude that for carbonyl groups the use of ECPs is not recommended, although their use could save time for very large systems, for instance in cluster chemistry. The reliance of NMR chemical shielding on dynamical effects, such as intramolecular rearrangements or trigonal twists, is also examined for H2Fe(CO)4, K+[HFe(CO)](-), HMn(CO)5 and HRe(CO)5. The accuracy of the theory is also examined for complexes with two dihydrogen ligands (Tp*RuH(H2)2 and [FeH(H2)(DMPE)2]+) and a ruthenium cluster, [H3Ru4(C6H6)4(CO)]+. It is shown that for all complexes studied in this work, the effect of the ligands on the chemical shielding of hydrogen coordinated to metal is suitably calculated, thus yielding a very good correlation between experimental chemical shifts and theoretical chemical shielding.

Quartic-Scaling Analytical Energy Gradient of Scaled Opposite-Spin Second-Order Møller−Plesset Perturbation Theory

The analytical gradient of the "scaled opposite spin" (SOS-) and "modified opposite spin" (MOS-) second-order Møller-Plesset perturbation theory (MP2) methods is derived and implemented. Both energy and the first derivative can be evaluated efficiently with a fourth-order scaling algorithm by using a combination of auxiliary basis expansions and Laplace transformation techniques as opposed to the traditional fifth-order approach of MP2. A statistical analysis of 178 small molecules suggests that the new gradient scheme provides geometries of MP2 quality, indicating the reliability of the method in general chemical applications. A more specific study of the group VI transition metal carbonyl complexes indicates that the new scheme improves the MP2 description relative to available experimental data and higher-order theories. The proposed gradient scheme thus endeavors to obtain improved structural features at reduced computational cost.