DFT studies of structural preference of coordinated ethylene in W(CO)3(PX3)2(CH2CH2) (X=H, CH3, F, Cl, Br, and I)

A set of phosphine complexes of the type W(CO)₃(PX₃)₂(CH₂CH₂) (X=H, CH₃, F, Cl, Br, and I) were investigated by density functional theory method (BP86) to examine the effect of the substituent X on the orientation of C-C vector of the ethylene ligand with respect to one of the metal-ligand bonds as well as the donation and the backdonation in the bonding ligands of phosphine and ethylene. When X=CH₃, H, F, and Cl, the ethylene C-C vector prefers to be coplanar with metal-phosphine bonds, while for the ethylene complexes containing PBr₃ and PI₃ ligands, the structural preference is coplanarity of the ethylene and the metal-carbonyl bonds. The molecular orbital calculations and natural bond orbital analysis were used to examine the structural consequences derived from these complexes. It can be concluded that the structural preferences in the complexes have a clear relation to electronic effects of phosphine ligands. Our calculations for halide phosphine complexes, particularly for PBr₃ and PI₃, allow us to conclude that in addition to electronic effects, steric factors can also affect the orientation of the ethylene ligand in complexes.     

Tris(2-cyanoethyl)tin(IV) bromide and tris(2-cyanoethyl)tin(IV) iodide,their structure,properties and reactions with adenosine,AMP and ATP

Complexes [Sn(CH₂CH₂CN)₃I] (1) and [SnBr(CH₂CH₂CN)₃] (2) have been obtained by the oxidation reactions of hexakis(2-cyanoethyl)ditin(III) by means of iodine and bromine. The complexes have been characterized by NMR and IR spectroscopy methods and X-ray crystallography. Both compounds consist of zigzag single-strand chains with a bridging 2-cyanoethyl ligand coordinating via the CH₂ group and N atom. The tin atoms are in a distorted trigonal bipyramidal environment with bromo or iodo ligands and a nitrogen atom occupying the axial coordination sites. The Sn(1)–N(3i) distances in complexes 1 and 2 are considerably longer than the tin-equatorial ligand bonds. The molecular and electronic structures and IR spectra of [SnBr(CH₂CH₂CN)₃] mononuclear and [SnBr(CH₂CH₂CN)₃]₂ dinuclear fragments of the complex have been studied by the DFT B3LYP method. The calculated interatomic distances for the entity containing a five-coordinate tin atom agree well with those found crystallographically. The compounds in water solutions form trigonal bipyramidal complexes containing aqua and hydroxo axial ligands. The interaction of these complexes with adenosine, 5′-adenosine monophosphate and 5′-adenosine triphosphate has been investigated.     

Density functional investigation and bonding analysis of pentacoordinated iron complexes with mixed cyano and carbonyl ligands

The equilibrium structures and vibrational frequencies of the iron complexes [Fe⁰(CN)_n(CO)_5?n]^n? and [Fe^II(CN)_n(CO)_5?n]^2?n (n = 0–5) have been calculated at the BP86 level of theory. The Fe⁰ complexes adopt trigonal bipyramidal structures with the cyano ligands occupying the axial positions, whereas corresponding Fe²⁺ complexes adopt square pyramidal structures with the cyano ligands in the equatorial positions. The calculated geometries and vibrational frequencies of the mixed iron Fe⁰ carbonyl cyanide complexes are in a very good agreement with the available experimental data. The nature of the Fe? CN and Fe? CO bonds has been analyzed with both charge decomposition and energy partitioning analysis. The results of energy partitioning analysis of the Fe? CO bonds shows that the binding interactions in Fe⁰ complexes have 50–55% electrostatic and 45–50% covalent character, whereas in Fe²⁺ 45–50% electrostatic and 50–55% covalent character. There is a significant contribution of the π‐ orbital interaction to the Fe? CO covalent bonding which increases as the number of the cyano groups increases, and the complexes become more negatively charged. This contribution decreases in going from Fe⁰ to Fe²⁺ complexes. Also, this contribution correlates very well with the C? O stretching frequencies. The Fe? CN bonds have much less π‐character (12–30%) than the Fe? CO bonds. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Relation between coordination geometry and stereoelectronic properties in DFT models of the CO-inhibited [FeFe]-hydrogenase cofactor

In this work DFT has been used to characterize model complexes structurally related to the CO-inhibited form (Hox-CO) of [FeFe]-hydrogenases.The investigation of a recently synthesized diiron complex ([Fe₂{MeSCH₂C(Me)(CH₂S)₂}(CN)₂(CO)₄]⁻, [M. Razavet, S.J. Borg, S.J. George, S.P. Best, S.A. Fairhurst, C.J. Pickett, Chem. Commun. 2002, 700-701]) that closely reproduces most features of the inhibited enzyme cofactor, led to the conclusion that the computation of DFT energy differences, as well as the comparison between computed and experimental IR and EPR spectra, does not allow to confidently distinguish among isomers differing for the position of CO and CN ligands, an issue which is relevant not only to fully understand the mechanism of CO-mediated inhibition of the enzyme, but more generally to further understand the factors affecting substrates coordination to the enzyme active site.The latter observation prompted us to probe the effect of the electronic properties of ligands on the structural features of a series of [Fe₂(SCH₂XCH₂S)(CN)₂(CO)₃(L)]ⁿ⁻ complexes related to the Hox-CO form of the enzyme but differing for the nature of L (CO, (CH₃)₂S, CH₃S⁻, CH₃O⁻ and F⁻) and X (CH₂, NH and O). Results revealed that the electronic properties of ligands, as well as the nature of the chelating group bridging the two iron atoms, can affect the coordination geometry of the distal metal center. In particular, it turned out that the inclusion of hard ligands in the Fe coordination sphere could be a viable strategy to selectively favour isomers featuring two CO groups trans to each other. On the other hand, the substitution of propanedithiolate with a di(thiomethyl)amine residue led to the selective stabilization of structures featuring a CN ligand in trans to the μ-CO group, thanks to the formation of an intramolecular hydrogen bond. The relevance of these DFT results for the design of novel biomimetic models of the CO-inhibited [FeFe]-hydrogenases active site is discussed.     

Elektronenreiche übergangsmetallkomplexe : IV. Dien-bis(phosphin)-molybdändicarbonyle

Dienes can replace the acetonitrile in (CH₃CN)₂Mo(PBu₃)₂,(CO)₂ or acetoni- trile and the one phosphine trans to the CO group in (CH₃CN)Mo(PBu₃)₃(CO)₂ under mild conditions. IR-, H NMR, ¹³C NMR and electronic spectra of the new (diene)Mo(PBu₃)₂(CO)₂ complexes are discussed and compared with similar compounds of other transition metals.     

Synthesen und Schwingungsspektren der homoleptischen Acetonitrilkomplex-Kationen [Au(NCCH3)2]+, [Pd(NCCH3)4]2+, [Pt(NCCH3)4]2+ und des Adduktes CH3CN · SbF5. Kristallstrukturen der Salze [M(NCCH3)4][SbF6]2 · CH3CN,M = Pd,Pt

The Syntheses and Vibrational Spectra of the Homoleptic Metal Acetonitrile Cations [Au(NCCH₃)₂]⁺, [Pd(NCCH₃)₄]²⁺, [Pt(NCCH₃)₄]²⁺, and the Adduct CH₃CN · SbF₅. The Crystal and Molecular Structures of [M(NCCH₃)₄][SbF₆]₂ · CH₃CN, M = Pd or Pt Solvolyses of the homoleptic metal carbonyl salts [M(CO)₄][Sb₂F₁₁]₂, M = Pd or Pt, in acetonitrile leads at 50 °C both to complete ligand exchange for the cations as well as to a conversion of the di-octahedral anion [Sb₂F₁₁]^– into [SbF₆]^– and the molecular adduct CH₃CN · SbF₅ according to: [M(CO)₄][Sb₂F₁₁]₂ + 7 CH₃CN → [M(NCCH₃)₄][SbF₆]₂ · CH₃CN + 2 CH₃CN · SbF₅ + 4 CO M = Pd, Pt The monosolvated [M(NCCH₃)₄][SbF₆]₂ · CH₃CN are obtained as single crystals from solution and are structurally characterized by single crystal x-ray diffraction. Both salts are isostructural. The cations are square planar but the N–C–C-sceletial groups of the ligands depart slightly from linearity. The new acetonitrile complexes as well as [Au(NCCH₃)₂][SbF₆] and the adduct CH₃CN · SbF₅ are completely characterized by vibrational spectroscopy.     

An investigation of the electron density of a Jahn–Teller‐distorted CrII cation: the crystal structure and charge density of hexakis(acetonitrile‐κN)chromium(II) bis(tetraphenylborate) acetonitrile disolvate

In the crystal structure of the title homoleptic Cr^II complex, [Cr(CH₃CN)₆](C₂₄H₂₀B)₂·CH₃CN, the [Cr(CH₃CN)₆]²⁺ cation is a high‐spin d⁴ complex with strong static, rather than dynamic, Jahn–Teller distortion. The electron density of the cation was determined by single‐crystal X‐ray refinements using aspherical structure factors from wavefunction calculations. The detailed picture of the electronic density allowed us to assess the extent and directionality of the Jahn–Teller distortion of the Cr^II cation away from idealized octahedral symmetry. The topological analysis of the aspherical d‐electron density about the Cr^II cation showed that there are significant valence charge concentrations along the axial Cr—N axes. Likewise, there were significant valence charge depletions about the Cr^II cation along the equatorial Cr—N bonds. These charge concentrations are in accordance with a Jahn–Teller‐distorted six‐coordinate complex.     

Metallomacrocycle (MacM) complex with cyanide as bridged ligand: Electronic structures of [MacMCN]n

The electronic structures of complexes and one‐dimensional metallomacrocycles with cyanide as bridged ligand, such as [MacM(CN)₂]^? and [MacM(CN)]_n [Mac=phthalocyanine, tetrabenzoporphyrine; M=Co(III), Rh(III)] have been investigated using density functional theory. The results of this study show that the intrinsic semiconductivity properties depend on the frontier bands. The valence band is composed by the π‐macrocycle orbital. The conduction band for the cobalt polymers is a mixture of orbitals between this metal and the cyanide ligand along of the stacking direction. However, in the rhodium polymers such a band is exclusively composed of the π* system of the macrocycles. © 2002 John Wiley & Sons, Inc. Int J Quantum Chem, 2002     

Spectral study of the dioxygen and carbonyl adducts of ferrous porphyrins ligated by neutral S-donors

A series of the six-coordinated ferrous porphyrin complexes (L)Fe(II)TPP(O₂) and (L)Fe(II)TPP(CO) (L, (CH₃)₂S, or C₂H₅SH, TPP, meso-tetraphenylporphyrin dianion) was prepared. UV–vis and FTIR spectroscopy were applied to follow the reaction of O₂ and CO adducts of Fe(II) porphyrins with neutral thiol and thioether. Using sublimed layers methodology and low temperature technique, as well as isotope substitution, the formation of six-coordinate complexes was monitored in situ. The comparison of CO and O₂ stretching frequencies of thiol and thioether adducts indicates that the degree of electron donation is similar for these ligands. The complexes of Me₂S and EtSH with Fe(TPP)(O₂) are stable at 150 K and slowly decompose at elevated temperatures. In contrast, the carbonyl complexes of Fe(Por) with Me₂S and EtSH are relatively stable and retain six-coordination at room temperature. The electronic effects of axial S-donor ligands on the coordinated O₂ and CO are discussed and compared with the effects of N- and O-donors.     

Study of allylic rearrangement in (μ-H)Os3(μ-O=CNRCH2CH=CH2)(CO)10 (R=H or CH3) clusters

The migration of the double bond in the allylcarboxamide ligands of (μ-H)Os₃(μ-O=CN RCH₂CH=CH₂) (CO)₁₀ (R=H (1) or CH₃ (2)), (μ-D)Os₃(μ-O=CNDCH₂CH=CH₂) (CO)₁₀, and (μ-H)Os₃(μ-O=CNHCD₂CH=CH₂)(CO)₁₀ clusters was studied by¹H,²H, and¹³C NMR spectroscopy. Neither μ-D nor ND groups in the deuterated complexes are directly involved in prototropic processes of allylic rearrangement. Initially, the deuterium atom of the CD₂ group migrates to the ψ-carbon atom of the allyl fragment to form the −CD=CH-CH₂D propenyl moiety, in which the deuterium and hydrogen atoms are gradually redistributed between the ψ-and β-carbon atoms. The triosmium cluster complexes containing the bridging carboxamide ligands O=CNRR' catalyze the allylic rearrangement ofN-allylacetamide. Based on the data obtained, the probable scheme of the allylic rearrangements in clusters1 and2 was proposed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2182–2186, November, 1999.     

Tricarbonyl Derivatives of Manganese(I) with Diphosphinite Chelating Ligands

Reaction of [MnBr(CO)₃L] [L = Ph₂POCH₂CH₂OPPh₂, L¹ , {(CH₃)₂CH}₂POCH₂CH₂OP{CH(CH₃)₂}₂, L² ] with AgO₃SCF₃ and AgO₂CCF₃ in dichloromethane afforded the new complexes [Mn(O₃SCF₃)(CO)₃L] and [Mn(O₂CCF₃)(CO)₃L], respectively. Substitution of O₃SCF₃ resulted in the new species [Mn(SCN)(CO)₃L], [Mn(NCCH₃)(CO)₃L](O₃SCF₃) and, in the case of L² , [Mn(CN)(CO)₃L²]. By contrast, any attempt to displace the O₂CCF₃ ligand in the same way was unsuccessful. After maintaining for some days the complex [Mn(CH₃CN)(CO)₃L¹](O₃SCF₃) in dichloromethane at room temperature, the new complex [MnCl(CO)₃L¹] was formed. All the new complexes were characterized by elemental analysis, mass spectrometry and IR and NMR spectroscopies. In the case of [Mn(O₃SCF₃)(CO)₃L¹], [Mn(O₂CCF₃) (CO)₃L¹], [MnCl(CO)₃L¹], [Mn(CH₃CN) (CO)₃L²] (O₃SCF₃), [Mn(CN)(CO)₃L²] and [Mn(O₂CCF₃)(CO)₃L²], together with the previously synthesized complex [MnBr(CO)₃L²], suitable crystals for X‐ray structural analysis were isolated. In all of them the Mn atom adopts six‐coordination by bonding to the three CO ligands, the two P atoms of L and either one C atom (CN), one oxygen atom (O₂CCF₃, O₃SCF₃), one N atom (CH₃CN, SCN) or the halogen atom (Cl, Br).     

Electric-field gradients and magnetic hyperfine parameters of square-pyramidal [M(CN)5]3− (M = Co,Rh, and Ir) complexes

Density functional self-consistent spin-polarized calculations with the discrete variational method were performed to obtain the electronic structure of the paramagnetic complexes [Co(CN)₅]^3?, [Rh(CN)₅]^3?, and [Ir(CN)₅]^3? of square-pyramidal geometry. All electrons were kept in the variational space. Electric-field gradients and magnetic hyperfine parameters at the metal site were computed with the molecular charge and spin densities obtained and compared with experimental values derived by electron paramagnetic resonance. It was found that the Fermi interaction is critically dependent on the angle between the axial and equatorial CN ligands. © 1995 John Wiley & Sons, Inc.     

Revisit of trinickel metal string complexes [Ni3L4X2] (L = dipyridylamido,diazaphenoxazine; X = NCS,CN) for quantum transport

Metal string complexes contain a linear metal‐atom chain in which the metal centers are coordinated by four equatorial and two axial ligands. With a variety of transition‐metal elements and ligands, the structural framework drives the flourishing of molecular design and properties. The one‐dimensional configuration makes the compounds suitable for the studies of quantum transport across molecular junctions. In this study, we report the conductance measurements and transmission spectra of three trinickel metal strings, [Ni₃(dpa)₄(NCS)₂] ( 1 ), [Ni₃(dzp)₄(NCS)₂] ( 2 ), and [Ni₃(dpa)₄(CN)₂] ( 3 ) (Hdpa = dipyridylamine, Hdzp, diazaphenoxazine) in which 1 is a prototypical compound, dzp of 2 represents an equatorial ligand more rigid than dpa of 1 , and ─CN is an axial ligand with a ligand‐field effect stronger than ─NCS of 1 . Measurement results of molecular junctions for 1 , 2 , and 3 are 2.69, 3.24, and 17.4 MΩ, respectively. The highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO–LUMO) gaps calculated by density functional theory in the gas phase for 1 , 2 , and 3 are about 2.65, 2.34, and 3.85 eV, respectively. Zero‐bias transmission spectra of 1 – 3 show that transmission peaks lie just above E_Fermi (the Fermi energy of the gold electrode), suggesting LUMO‐dominant transport pathways. The transmission peaks at E_Fermi are associated with LUMO+2 found in the gas phase. LUMOs in the free space are located at nearly 1 eV below E_Fermi. The shift of molecular orbitals from their isolated form and the alignment of LUMO+2 with the electrode Fermi level manifest the importance and significant of the electrodes' self‐energy on electron transport.     

Synthesis,structure, redox property and ligand replacement reaction of ruthenium(II) complexes containing a terpyridyl ligand with a redox active moiety

Ruthenium(II) complexes bearing a redox-active tridentate ligand 4′-(2,5-dimethoxyphenyl)-2,2′:6′,2′′-terpyridine (tpyOMe), analogous to terpyridine, and 2,2′-bipyridine (bpy) were synthesized by the sequential replacement of Cl by CH₃CN and CO on the complex. The new ruthenium complexes were characterized by various methods including IR and NMR. The molecular structures of [Ru(tpyOMe)(bpy)(CH₃CN)]²⁺ and two kinds of [Ru(tpyOMe)(bpy)(CO)]²⁺ were determined by X-ray crystallography. The incorporation of monodentate ligands (Cl, CH₃CN and CO) regulated the energy levels of the MLCT transitions and the metal-centered redox potentials of the complexes. The kinetic data observed in this study indicates that the ligand replacement reaction of [Ru(tpyOMe)(bpy)Cl]⁺ to [Ru(tpyOMe)(bpy)(CH₃CN)]²⁺ proceeds by a solvent-assisted dissociation process.     

Combined XPS and AFM study of cluster-containing polymers based on Rh

Rh₆- monomer and polymer-immobilized complexes have been characterized using XPS and AFM. Polymer-immobilized clusters were obtained by the reaction of Rh₆(CO)₁₅CH₃CN with copolymer of allyldiphenylphosphine and styrene. AFM study shows the change of surface morphology of the above copolymers. XPS data demonstrated the change of charge state of Rh atoms under monosubstitution of the CO-group for Rh₆- monomer complexes as well as in copolymer cluster complexe after the catalysis process of hydrogenation.     

Synthesis and Reactivity of Mononuclear Iron Models of [Fe]‐Hydrogenase that Contain an Acylmethylpyridinol Ligand

[Fe]‐hydrogenase has a single iron‐containing active site that features an acylmethylpyridinol ligand. This unique ligand environment had yet to be reproduced in synthetic models; however the synthesis and reactivity of a new class of small molecule mimics of [Fe]‐hydrogenase in which a mono‐iron center is ligated by an acylmethylpyridinol ligand has now been achieved. Key to the preparation of these model compounds is the successful C?O cleavage of an alkyl ether moiety to form the desired pyridinol ligand. Reaction of solvated complex [(2‐CH₂CO‐6‐HOC₅H₃N)Fe(CO)₂(CH₃CN)₂]⁺(BF₄)^? with thiols or thiophenols in the presence of NEt₃ yielded 5‐coordinate iron thiolate complexes. Further derivation produced complexes [(2‐CH₂CO‐6‐HOC₅H₃N)Fe(CO)₂(SCH₂CH₂OH)] and [(2‐CH₂CO‐6‐HOC₅H₃N)Fe(CO)₂(CH₃COO)], which can be regarded as models of FeGP cofactors of [Fe]‐hydrogenase extracted by 2‐mercaptoethanol and acetic acid, respectively. When the derivative complexes were treated with HBF₄?Et₂O, the solvated complex was regenerated by protonation of the thiolate ligands. The reactivity of several models with CO, isocyanide, cyanide, and H₂ was also investigated.     

Synthesis and properties of cobalt(III) complexes of 3,14-dimethyl-2,6,13,17-tetraazatricyclo[14,4,0,0]docosane

The octahedral cobalt(III) complexes, [Co(L)(int)₂]Cl · 3H₂O (1), [Co(L)(NCS)₂]NCS · H₂O (2) and [Co(L)(NCO)₂]NCO · H₂O (3) (L = 3,14-dimethyl-2,6,13,17-tetraazatricyclo[14,4,0^1.18,0^7.12]docosane, int = isonicotinate) were obtained by the reactions of [Co(L)Cl₂]Cl · 4H₂O with the corresponding ligands. The X-ray analysis of 1 shows that the complex has an octahedral geometry formed by coordination of four secondary amines of the macrocycle and two oxygen atoms of the axial isonicotinate ligands. Complex 2 also has an octahedral geometry with four secondary amines of the macrocycle and two nitrogen atoms of the axial thiocyanate ligands. Electronic spectra of the complexes also exhibit a low-spin octahedral geometry. Cyclic voltammetry of the complexes undergoes a one-electron wave corresponding to a Co^III/Co^II process. The electronic spectra and electrochemical behaviors of the complexes are significantly affected by the nature of the axial ligands.     

Study of the nature of the interaction of CH3CN with Lewis acids

The unperturbed ν⁰ (CN) stretching frequencies of CH₃CN in 18 complexes with Lewis acids are correlated with ν (CN) frequencies in cobalticyanides and with cation parameters which measure σ and π interactions. The results indicate that the nature of the interaction is predominantly of the σ donor—acceptor type wib no detectable π back-donation from the cation to the CN ligand.     

Reactions of the molybdenum(II) dicarbonyl complexes with mercury(II) halides and pseudohalides

The reactions of the molybdenum(II) dicarbonyl complexes, [MoBr(π-allyl)(CO)₂(L)₂] (L = CH₃CN, py) and (MoBr(π-allyl)(CO)₂(L,L)] (L,L = bipy, phen, dppe) with HgX₂ (X = Cl, CN, SCN) give several new complexes via a displacement reaction involving Br or/and L ligands or a simple adduct formation reaction.